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WO2025205497A1 - Lithium ion secondary battery and lithium ion secondary battery module - Google Patents

Lithium ion secondary battery and lithium ion secondary battery module

Info

Publication number
WO2025205497A1
WO2025205497A1 PCT/JP2025/011219 JP2025011219W WO2025205497A1 WO 2025205497 A1 WO2025205497 A1 WO 2025205497A1 JP 2025011219 W JP2025011219 W JP 2025011219W WO 2025205497 A1 WO2025205497 A1 WO 2025205497A1
Authority
WO
WIPO (PCT)
Prior art keywords
ion secondary
secondary battery
active material
electrode active
negative electrode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/JP2025/011219
Other languages
French (fr)
Japanese (ja)
Inventor
円花 藤原
佳麗 劉
哲志 小野
健宏 野口
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Envision AESC Japan Ltd
Original Assignee
AESC Japan Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by AESC Japan Co Ltd filed Critical AESC Japan Co Ltd
Publication of WO2025205497A1 publication Critical patent/WO2025205497A1/en
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • ⁇ Method 2> The lithium ion secondary battery is placed in a thermostatic chamber at 25°C, and then the lithium ion secondary battery is charged and discharged in accordance with the ⁇ charge and discharge cycle> described below, and the first discharge capacity is measured. Next, the lithium ion secondary battery is repeatedly charged and discharged in accordance with the ⁇ charge and discharge cycle> described below until a total of 499 cycles have been reached. Next, the lithium ion secondary battery is charged and discharged in accordance with the ⁇ charge and discharge cycle> described below, and the discharge capacity is measured for the 500th cycle. Next, the capacity retention rate R25 is calculated using the following formula (2).
  • the lithium ion secondary battery of this embodiment has the above-described configuration, and thus can improve cycle characteristics.
  • a positive electrode tab 9 is connected to the positive electrode current collector 3, and a negative electrode tab 8 is connected to the negative electrode current collector 4.
  • the positive electrode tab 9 and the negative electrode tab 8 are extended outside the container.
  • An electrolyte solution is injected and sealed inside the container.
  • the container may also house an electrode group consisting of multiple electrode pairs stacked together.
  • the lithium ion secondary battery can be fabricated according to a known method.
  • the electrode can be, for example, a laminate or a wound body.
  • the exterior can be a metal exterior or an aluminum laminate exterior.
  • the battery may have any shape, such as a laminate, coin, button, sheet, cylindrical, rectangular, or flat shape, but a laminate battery is preferred.
  • the electrolytic solution contains an electrolyte and an organic solvent.
  • the electrolytic solution contains lithium bis(fluorosulfonyl)imide (hereinafter also referred to as LiFSI) as the electrolyte.
  • examples of electrolytes other than LiFSI include lithium hexafluorophosphate (LiPF 6 ), lithium difluorobis(oxalato)phosphate (LiDODFP), lithium difluorophosphate (LiPO 2 F 2 ), LiClO 4 , LiBF 4 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiB 10 Cl 10 , LiAlCl 4 , LiCl, LiBr, LiB(C 2 H 5 ) 4 , CH 3 SO 3 Li, LiC 4 F 9 SO 3 , and Li(CF 3 SO 2 ) 2 .
  • LiPF 6 lithium hexafluorophosphate
  • LiDODFP lithium difluorobis(oxalato)phosphate
  • LiPO 2 F 2 lithium difluorophosphate
  • LiClO 4 LiBF 4 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSb
  • the lithium salt of a lower fatty acid, a lower carboxylic acid, or a mixture thereof may contain one or more compounds selected from the group consisting of N, a lithium salt of a lower fatty acid, and a lithium salt of a lower carboxylic acid, and preferably contains one or more compounds selected from the group consisting of LiPF6 and LiCl, and more preferably contains LiPF6 .
  • the organic solvent is not particularly limited as long as it can dissolve the electrolyte.
  • organic solvents include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC); lactones such as ⁇ -butyrolactone and ⁇ -valerolactone; ethers such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide; oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; and acetonitrile.
  • carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (
  • the solvent contains one or more solvents selected from the group consisting of nitrogen-containing solvents such as nitromethane, formamide, and dimethylformamide; organic acid esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and ethyl propionate; phosphate esters such as phosphate triesters; diglymes; triglymes; sulfolanes such as sulfolane and methylsulfolane; oxazolidinones such as 3-methyl-2-oxazolidinone; and sultones such as 1,3-propane sultone, 1,4-butane sultone, and naphtha sultone, preferably carbonates, and more preferably one or more solvents selected from the group consisting of EC and EMC.
  • nitrogen-containing solvents such as nitromethane, formamide, and dimethylformamide
  • organic acid esters such as
  • the concentration of LiFSI in the electrolyte during production of the lithium ion secondary battery is preferably 0.7% by mass or more and 4.8% by mass or less, more preferably 0.8% by mass or more and 4.5% by mass or less, even more preferably 0.9% by mass or more and 4.0% by mass or less, even more preferably 1.0% by mass or more and 3.5% by mass or less, and even more preferably 1.0% by mass or more and 3.2% by mass or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the concentration of LiPF6 in the electrolyte solution during production of the lithium ion secondary battery is preferably 1.0 mass% or more, more preferably 5.0 mass% or more, even more preferably 10.0 mass% or more, still more preferably 10.5 mass% or more, still more preferably 11.0 mass% or more, and still more preferably 11.5 mass% or more, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the LiPF6 concentration (at the time of manufacture) is preferably 20.0 mass % or less, more preferably 18.0 mass % or less, even more preferably 15.0 mass % or less, still more preferably 14.0 mass % or less, still more preferably 13.0 mass % or less, and still more preferably 12.5 mass % or less, from the viewpoint of reducing corrosion of the battery components.
  • the LiPF6 concentration (at the time of production) is preferably 1.0 mass % or more and 20.0 mass % or less, more preferably 5.0 mass % or more and 18.0 mass % or less, even more preferably 10.0 mass % or more and 15.0 mass % or less, still more preferably 10.5 mass % or more and 14.0 mass % or less, still more preferably 11.0 mass % or more and 13.0 mass % or less, and still more preferably 11.5 mass % or more and 12.5 mass % or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery and reducing corrosion of the battery components.
  • the content of the electrolyte in the lithium ion secondary battery is preferably 15 parts by mass or more and 60 parts by mass or less, more preferably 20 parts by mass or more and 55 parts by mass or less, even more preferably 25 parts by mass or more and 50 parts by mass or less, and even more preferably 30 parts by mass or more and 45 parts by mass or less, when the total content of the negative electrode active material and the positive electrode active material in the lithium ion secondary battery is taken as 100 parts by mass, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the negative electrode of this embodiment includes a negative electrode active material layer. From the viewpoint of further improving the battery performance of the lithium ion secondary battery, the negative electrode of this embodiment preferably includes a negative electrode current collector and the negative electrode active material layer of this embodiment.
  • the negative electrode active material contained in the negative electrode active material layer has an SEI (Solid Electrolyte Interphase) film on at least a part of its surface, and preferably has an SEI film on its entire surface.
  • the SEI film is formed by decomposition of the electrolyte on the surface of the negative electrode during initial charge/discharge.
  • the SEI film is a film formed on at least a portion of the surface of the negative electrode active material by decomposition products of the electrolyte and electrolyte additives.
  • the SEI film functions to insert or extract lithium ions into or from the negative electrode, while also functioning to reduce further decomposition of the electrolyte on the surface of the negative electrode.
  • an SEI film can be formed on at least a portion of the surface of the negative electrode (negative electrode active material) by the method described in the "Initial Charging and Discharging of Lithium-Ion Secondary Battery" section in the Examples.
  • the lithium-ion secondary battery of this embodiment has an SEI film on at least a portion of the surface of the negative electrode active material contained in the negative electrode active material layer, and is therefore a lithium-ion secondary battery after at least initial charging and discharging.
  • the negative electrode active material layer of the present embodiment preferably contains the negative electrode active material of the present embodiment and a binder, and more preferably contains the negative electrode active material of the present embodiment, a binder, and a conductive additive.
  • the thickness of the negative electrode active material layer in this embodiment is preferably 10 ⁇ m or more and 250 ⁇ m or less, more preferably 15 ⁇ m or more and 200 ⁇ m or less, even more preferably 20 ⁇ m or more and 100 ⁇ m or less, and even more preferably 25 ⁇ m or more and 75 ⁇ m or less.
  • the density of the negative electrode active material layer of this embodiment is preferably 0.50 g/ cm3 or more and 3.00 g/ cm3 or less, more preferably 1.00 g/ cm3 or more and 2.50 g/cm3 or less , and even more preferably 1.30 g/ cm3 or more and 2.00 g/ cm3 or less.
  • the negative electrode active material of the present embodiment preferably contains one or more materials selected from the group consisting of a carbon material, a lithium-based metal material, a Si-based material, and a conductive polymer material, more preferably contains one or more materials selected from the group consisting of a carbon material and a Si-based material, and even more preferably contains both a carbon material and a Si-based material.
  • Examples of the carbon material of the present embodiment include graphite powder, hard carbon, soft carbon, and any mixture thereof, and graphite powder is preferred.
  • Si-based material of the present embodiment examples include silicon oxide particles and Si-C composite particles containing silicon and a carbon material (hereinafter also referred to as Si-C composite particles), and preferably contains Si-C composite particles from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the content of the negative electrode active material in the negative electrode active material layer of this embodiment when the total amount of the negative electrode active material layer is taken as 100.0 parts by mass, is preferably 50.0 parts by mass or more and 100.0 parts by mass or less, more preferably 75.0 parts by mass or more and 99.0 parts by mass or less, even more preferably 85.0 parts by mass or more and 98.5 parts by mass or less, even more preferably 90.0 parts by mass or more and 98.0 parts by mass or less, and even more preferably 95.0 parts by mass or more and 97.5 parts by mass or less.
  • the negative electrode active material of this embodiment preferably includes a negative electrode active material (A) and a negative electrode active material (B) of a type different from the negative electrode active material (A), from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the negative electrode active material (A) preferably contains a carbon material, more preferably contains graphite powder, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the volume-based median diameter D50 of the negative electrode active material (A) as measured by a laser diffraction scattering method is preferably 3.0 ⁇ m or more and 30.0 ⁇ m or less, more preferably 5.0 ⁇ m or more and 27.5 ⁇ m or less, even more preferably 7.5 ⁇ m or more and 22.5 ⁇ m or less, still more preferably 8.0 ⁇ m or more and 15.5 ⁇ m or less, and still more preferably 9.0 ⁇ m or more and 12.0 ⁇ m or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the graphite powder of this embodiment preferably contains graphite powder (A1) and a type of graphite powder (A1') different from the graphite powder (A1).
  • the graphite powder of this embodiment more preferably contains graphite powder (A1) and graphite powder (A2) having a volume-based median diameter D50 measured by a laser diffraction scattering method different from that of the graphite powder (A1), and the median diameter D50 of the graphite powder (A1) is larger than the median diameter D50 of the graphite powder (A2).
  • the ratio of D2 to D1 , D2 / D1 is preferably 0.40 or more and less than 1.0, more preferably 0.45 or more and 0.90 or less, even more preferably 0.50 or more and 0.80 or less, even more preferably 0.55 or more and 0.75 or less, and still more preferably 0.60 or more and 0.70 or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the volume-based median diameter D50 of the negative electrode active material (B) as measured by a laser diffraction scattering method is preferably 1.0 ⁇ m or more and 20.0 ⁇ m or less, more preferably 1.5 ⁇ m or more and 19.0 ⁇ m or less, even more preferably 2.5 ⁇ m or more and 17.0 ⁇ m or less, even more preferably 3.5 ⁇ m or more and 11.0 ⁇ m or less, and still more preferably 4.0 ⁇ m or more and 9.0 ⁇ m or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the binder in the negative electrode active material layer of this embodiment preferably contains one or more types selected from the group consisting of fluororesin, polycarboxylic acid polymer, and synthetic rubber, more preferably contains one or more types selected from the group consisting of PVDF, polycarboxylic acid polymer, and SBR, even more preferably contains a polycarboxylic acid polymer, and even more preferably contains poly(meth)acrylic acid.
  • the conductive additive in the negative electrode active material layer of this embodiment includes, for example, one or more selected from the group consisting of carbon materials such as carbon fibers such as carbon nanofibers, carbon blacks such as acetylene black and ketjen black, activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes.
  • the conductive additive in the negative electrode active material layer of this embodiment preferably includes a carbon material, more preferably includes carbon nanotubes, and even more preferably includes single-walled carbon nanotubes, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the negative electrode current collector of this embodiment includes, for example, one or more selected from the group consisting of copper, stainless steel, nickel, titanium, and alloys thereof.
  • the negative electrode current collector may be in the form of, for example, a foil, a flat plate, or a mesh.
  • the thickness of the negative electrode current collector is not particularly limited, but is, for example, 1 ⁇ m or more and 50 ⁇ m or less.
  • the method for producing the negative electrode is not particularly limited and can be carried out according to a generally known method, for example, the method described in the Examples.
  • the positive electrode of this embodiment includes a positive electrode active material layer. From the viewpoint of further improving the battery performance of the lithium ion secondary battery, the positive electrode of this embodiment preferably includes a positive electrode current collector and the positive electrode active material layer of this embodiment.
  • the positive electrode active material layer of the present embodiment preferably contains the positive electrode active material of the present embodiment and a binder, and more preferably contains the positive electrode active material of the present embodiment, a binder, and a conductive additive.
  • the thickness of the positive electrode active material layer in this embodiment is preferably 10 ⁇ m or more and 250 ⁇ m or less, more preferably 15 ⁇ m or more and 200 ⁇ m or less, even more preferably 20 ⁇ m or more and 100 ⁇ m or less, and even more preferably 25 ⁇ m or more and 75 ⁇ m or less.
  • the density of the positive electrode active material layer of this embodiment is preferably 1.0 g/cm or more and 6.0 g/cm or less, more preferably 2.0 g/cm or more and 5.0 g/cm or less , and even more preferably 2.5 g/cm or more and 4.5 g/cm or less .
  • Examples of composite oxides of lithium and transition metals include lithium-nickel-cobalt-manganese composite oxide, lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-manganese-nickel composite oxide, and lithium-nickel-cobalt-aluminum composite oxide.
  • Examples of transition metal sulfides include TiS 2 , FeS, and MoS 2 .
  • Examples of transition metal oxides include MnO, V 2 O 5 , V 6 O 13 , and TiO 2 .
  • the content of the positive electrode active material in the positive electrode active material layer of this embodiment when the entire positive electrode active material layer is taken as 100.0 parts by mass, is preferably 50.0 parts by mass or more and 99.9 parts by mass or less, more preferably 75.0 parts by mass or more and 99.5 parts by mass or less, even more preferably 85.0 parts by mass or more and 99.0 parts by mass or less, even more preferably 90.0 parts by mass or more and 98.5 parts by mass or less, and even more preferably 95.0 parts by mass or more and 98.0 parts by mass or less.
  • the positive electrode active material contained in the positive electrode active material layer preferably contains particles (C) containing one or more kinds selected from particles (C1) constituted by a single crystal of a lithium-nickel-cobalt-manganese composite oxide and particles (C2) constituted by a polycrystal of a lithium-nickel-cobalt-manganese composite oxide.
  • the content of nickel in particles (C) is preferably 80 mol or more, more preferably 80 mol or more and 99 mol or less, even more preferably 82 mol or more and 99 mol or less, even more preferably 84 mol or more and 98 mol or less, even more preferably 85 mol or more and 96 mol or less, even more preferably 86 mol or more and 95 mol or less, and even more preferably 88 mol or more and 94 mol or less, when the total content of nickel, cobalt, and manganese in particles (C) is taken as 100 mol.
  • the content of cobalt in particles (C) is preferably 0.5 mol or more and 10 mol or less, more preferably 1 mol or more and 10 mol or less, even more preferably 2 mol or more and 10 mol or less, even more preferably 2.5 mol or more and 10 mol or less, even more preferably 3 mol or more and 8 mol or less, and even more preferably 4 mol or more and 6 mol or less, when the total content of nickel, cobalt, and manganese in particles (C) is taken as 100 mol.
  • the manganese content in particles (C) is preferably 0.5 mol or more and 10 mol or less, more preferably 1 mol or more and 10 mol or less, even more preferably 2 mol or more and 10 mol or less, even more preferably 2.5 mol or more and 10 mol or less, even more preferably 3 mol or more and 8 mol or less, and even more preferably 4 mol or more and 6 mol or less, when the total content of nickel, cobalt, and manganese in particles (C) is taken as 100 mol.
  • the ratio mN/(mC+mM) of the number of moles of nickel mN to the sum of the number of moles of cobalt mC and the number of moles of manganese mM is preferably 4 or more and 50 or less, more preferably 4.5 or more and 25 or less, even more preferably 5 or more and 16 or less, even more preferably 7 or more and 12 or less, and even more preferably 8 or more and 11 or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the binder in the positive electrode active material layer of this embodiment includes, for example, one or more selected from the group consisting of fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), polyvinyl fluoride (PVF), and copolymers of vinylidene fluoride and hexafluoropropylene; polycarboxylic acid polymers such as poly(meth)acrylic acid; conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles; synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR); and polysaccharides such as carboxymethyl cellulose (CMC), xant
  • the binder in the positive electrode active material layer of this embodiment preferably contains one or more types selected from the group consisting of fluororesin, polycarboxylic acid polymer, and synthetic rubber, more preferably contains one or more types selected from the group consisting of PVDF, polycarboxylic acid polymer, and SBR, and even more preferably contains PVDF.
  • the content of the binder in the positive electrode active material layer of this embodiment is preferably 0.05 parts by mass or more and 10.0 parts by mass or less, more preferably 0.1 parts by mass or more and 5.0 parts by mass or less, even more preferably 0.2 parts by mass or more and 2.5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 2.0 parts by mass or less, when the total amount of the positive electrode active material layer is taken as 100.0 parts by mass.
  • the conductive additive in the positive electrode active material layer of this embodiment includes, for example, one or more selected from the group consisting of carbon materials such as carbon fibers such as carbon nanofibers, carbon blacks such as acetylene black and ketjen black, activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes.
  • the conductive additive in the positive electrode active material layer of this embodiment preferably includes a carbon material, more preferably includes carbon nanotubes, and even more preferably includes single-walled carbon nanotubes, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the content of the conductive additive in the positive electrode active material layer of this embodiment is preferably 0.05 parts by mass or more and 10.0 parts by mass or less, more preferably 0.1 parts by mass or more and 5.0 parts by mass or less, even more preferably 0.2 parts by mass or more and 2.5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 2.0 parts by mass or less, when the total amount of the positive electrode active material layer is taken as 100.0 parts by mass.
  • the positive electrode current collector of this embodiment includes, for example, one or more selected from the group consisting of aluminum, stainless steel, nickel, titanium, and alloys thereof.
  • the positive electrode current collector may be in the form of, for example, a foil, a flat plate, or a mesh.
  • the thickness of the positive electrode current collector is not particularly limited, but is, for example, 1 ⁇ m or more and 50 ⁇ m or less.
  • the method for producing the positive electrode is not particularly limited and can be carried out according to a generally known method, for example, the method described in the Examples.
  • the lithium ion secondary battery of this embodiment includes an electrolyte, a positive electrode, and a negative electrode, and preferably further includes a separator.
  • the separator is not particularly limited as long as it can be used in lithium ion secondary batteries, and generally known separators can be used.
  • the separator preferably includes a substrate and a ceramic layer provided on at least one surface of the substrate, from the viewpoints of improving heat resistance and reducing thermal shrinkage of the separator.
  • the substrate may be, for example, a porous polyolefin film made of polyethylene, polypropylene, or a laminate of these.
  • the ceramic layer can be formed, for example, by applying a ceramic layer-forming material to a substrate and drying it.
  • the ceramic layer-forming material can be, for example, a material obtained by dispersing or dissolving an inorganic filler and a binder in a solvent.
  • the inorganic filler and binder are not particularly limited as long as they are known materials used in separators for lithium-ion secondary batteries.
  • the concentration of LiFSI in the electrolyte solution by ⁇ Method 1> is 0.6 mass % or more, preferably 0.7 mass % or more, more preferably 0.8 mass % or more, even more preferably 0.9 mass % or more, still more preferably 1.0 mass % or more, still more preferably 1.1 mass % or more, still more preferably 1.2 mass % or more, still more preferably 1.3 mass % or more, and still more preferably 1.4 mass % or more, from the viewpoint of improving the cycle characteristics of the lithium ion secondary battery.
  • the concentration of LiFSI in the electrolyte by ⁇ Method 1> is preferably 0.6 mass % or more and 5.0 mass % or less, more preferably 0.7 mass % or more and 4.0 mass % or less, even more preferably 0.8 mass % or more and 3.0 mass % or less, even more preferably 0.9 mass % or more and 3.0 mass % or less, even more preferably 1.0 mass % or more and 3.0 mass % or less, even more preferably 1.1 mass % or more and 3.0 mass % or less, even more preferably 1.2 mass % or more and 3.0 mass % or less, even more preferably 1.3 mass % or more and 3.0 mass % or less, and even more preferably 1.4 mass % or more and 2.7 mass % or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
  • the capacity retention rate R25 at 25°C is, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery, preferably 87.0% or more, more preferably 87.5% or more, even more preferably 88.0% or more, even more preferably 88.5% or more, even more preferably 89.0% or more, even more preferably 89.5% or more, even more preferably 90.0% or more, even more preferably 90.5% or more, even more preferably 91.0% or more, even more preferably 91.5% or more, and even more preferably 92.0% or more.
  • the upper limit of the capacity retention rate R 25 at 25° C. is not particularly limited, but is, for example, less than 100%, and may be 99.0% or less, 98.0% or less, or 95.0% or less.
  • the lithium ion secondary battery is charged at 30 mA until it reaches an upper limit voltage of 4.25 V. After the upper limit voltage of 4.25 V is reached, the lithium ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging. The lithium ion secondary battery is then discharged at a constant current of 30 mA until it reaches a lower limit voltage of 2.5 V.
  • the lithium-ion secondary battery module of this embodiment includes the lithium-ion secondary battery of this embodiment.
  • the lithium-ion secondary battery module of this embodiment preferably includes two or more lithium-ion secondary batteries of this embodiment connected in series or parallel.
  • the lithium-ion secondary battery module of this embodiment more preferably further includes a housing capable of accommodating two or more lithium-ion secondary batteries of this embodiment connected in series or parallel.
  • the lithium-ion secondary battery module of this embodiment more preferably further includes one or more devices selected from the group consisting of a protection circuit that protects the lithium-ion secondary battery from overcurrent, a balancing circuit that equalizes the voltage between the electrodes of the lithium-ion secondary battery, a controller that controls the lithium-ion secondary battery, a cooler that can cool the lithium-ion secondary battery, and a heater that can heat the lithium-ion secondary battery.
  • a protection circuit that protects the lithium-ion secondary battery from overcurrent
  • a balancing circuit that equalizes the voltage between the electrodes of the lithium-ion secondary battery
  • a controller that controls the lithium-ion secondary battery
  • a cooler that can cool the lithium-ion secondary battery
  • a heater that can heat the lithium-ion secondary battery.
  • the lithium-ion secondary battery module of this embodiment can be used in a battery system comprising two or more electrically connected lithium-ion secondary battery modules and a battery control system.
  • battery systems include battery packs, stationary storage battery systems, automotive power storage battery systems, automotive auxiliary storage battery systems, and emergency power storage battery systems.
  • the negative electrode active material (A) was a combination of the following graphite powder (A1) and graphite powder (A2).
  • Graphite powder (A1) As the graphite powder (A1), artificial graphite particles containing amorphous carbon on the surface were used. As the graphite powder (A1), the following graphite powder 1 was used. Graphite powder 1 (artificial graphite particles containing amorphous carbon on the surface, median diameter D 50 : 14.0 ⁇ m)
  • the negative electrode active material (B) used was the following Si—C composite particles (hereinafter also referred to as Si/C particles).
  • the Si--C composite particles used were the following Si/C particles 1.
  • Si/C particles 1 (median diameter D 50 : 4.8 ⁇ m, particles prepared according to the ⁇ Preparation of Si/C particles 1> below)
  • the positive electrode active material used was the following positive electrode active material 1.
  • Solvent 1 Ethylene carbonate (hereinafter also referred to as EC)
  • Solvent 2 Ethyl methyl carbonate (hereinafter also referred to as EMC)
  • Electrolyte Lithium hexafluorophosphate (LiPF 6 )
  • Electrolyte Lithium bis(fluorosulfonyl)imide (LiFSI)
  • Separator 10 ⁇ m thick microporous polyethylene film with ceramic coating on both sides
  • Negative electrode current collector copper foil (thickness: 8 ⁇ m)
  • Binder Polyacrylic acid (hereinafter referred to as PAA)
  • Conductive additive single-walled carbon nanotubes (hereinafter also referred to as CNTs)
  • Solvent Pure water
  • Positive electrode current collector aluminum foil (thickness: 12 ⁇ m)
  • Binder Polyvinylidene fluoride (hereinafter also referred to as PVDF)
  • Conductive additive single-walled carbon nanotubes (hereinafter also referred to as CNTs)
  • Solvent N-methyl-2-pyrrolidone (hereinafter also referred to as NMP)
  • ⁇ Method for measuring particle diameters of positive electrode active material and negative electrode active material> Using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, model number: SALD-2300), the volume-based median diameter D 50 of each of the positive electrode active material and the negative electrode active material was measured by laser diffraction scattering.
  • the median diameter D 50 of the positive electrode active material was measured after suspending the positive electrode active material in a dispersion medium (0.1% by mass sodium hexametaphosphate aqueous solution) and ultrasonically dispersing it.
  • the median diameter D 50 of the negative electrode active material was measured after suspending the negative electrode active material in a dispersion medium (0.1% by mass sodium hexametaphosphate aqueous solution) and ultrasonically dispersing it. The measurement was performed five times, and the average value was taken as the median diameter D 50 .
  • the electrolyte solutions to be used in the lithium ion secondary batteries of each example were prepared according to the following procedure. Ethylene carbonate and ethyl methyl carbonate were mixed in a mass ratio of 30:70 (EC:EMC) to obtain a mixed solvent. Lithium hexafluorophosphate (LiPF 6 ) was dissolved in the obtained mixed solvent to a content of 12 mass%. Furthermore, lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in the mixed solvent to obtain the LiFSI concentration (at the time of preparation) shown in Table 1, thereby preparing the electrolyte solutions of each example.
  • LiPF 6 Lithium hexafluorophosphate
  • LiFSI lithium bis(fluorosulfonyl)imide
  • the positive electrodes to be used in the lithium ion secondary batteries of each example were fabricated in the following manner.
  • the positive electrode slurry was applied to a 12 ⁇ m thick aluminum foil positive electrode current collector in an amount such that the initial charge capacity per unit area was 4.0 mAh/cm 2.
  • the applied positive electrode slurry was then dried to obtain a positive electrode laminate.
  • the positive electrode laminate was pressed with a pressure such that the density of the positive electrode active material layer was 3.5 g/cm 3 , to produce each positive electrode of each example.
  • the negative electrodes to be used in the lithium ion secondary batteries of each example were fabricated in the following manner.
  • the negative electrode slurry was applied to an 8 ⁇ m thick copper foil negative electrode current collector in an amount such that the initial charge capacity per unit area was 4.3 mAh/cm 2.
  • the applied negative electrode slurry was then dried to obtain a negative electrode laminate.
  • the negative electrode laminate was pressed at a pressure such that the density of the negative electrode active material layer was 1.65 g/cm 3 , to produce each negative electrode of each example.
  • the lithium ion secondary batteries of each example were fabricated in the following manner.
  • One double-sided coated positive electrode and two single-sided coated negative electrodes were arranged with the coated surfaces facing each other through a separator, and stacked in the following order: negative electrode, separator, positive electrode, separator, negative electrode.
  • the stack thus produced was then wrapped in a laminated outer casing formed by processing a film primarily composed of aluminum.
  • the aluminum foil and copper foil cut out for current collection protruded from the laminated film.
  • the edge containing the protruding current collection foil and the other two edges were then heat-sealed to produce a laminated cell with only one edge open.
  • a predetermined amount of the electrolyte solution prepared above was poured into the opening of the laminated cell, and the laminated cell was then sealed under reduced pressure to produce a laminated lithium ion secondary battery.
  • the amount of the electrolyte solution to be injected was set so that the amount of the electrolyte solution was 30 parts by mass when the total amount of the positive electrode active material and the negative electrode active material was 100 parts by mass.
  • the lithium ion secondary battery of each example was initially charged and discharged under the following conditions to form an SEI film on the surface of the negative electrode active material, thereby obtaining the lithium ion secondary battery of each example after initial charge and discharge.
  • the charge and discharge of the lithium ion secondary battery was performed using a charge and discharge device in an environment at a temperature of 25°C.
  • the lithium ion secondary battery of each example was charged at a charging current of 0.05 C up to a battery voltage of 3.2 V, and then left to stand for 12 hours to perform pre-charging. Next, constant current charging was performed at a charging current of 0.05 C until the battery voltage reached 4.25 V.
  • the lithium-ion secondary battery was returned to an environment at a temperature of 25°C and constant current discharge was performed at a discharge current of 1 C until the battery voltage reached 2.5 V.
  • constant current discharge was performed at a discharge current of 0.33 C until the battery voltage reached 2.5 V.
  • the battery was left for 10 minutes.
  • constant current charging was performed at a charging current of 0.33 C until the battery voltage reached 4.25 V.
  • constant voltage charging was performed until the current value decreased to 0.05 C.
  • 10 minutes after the end of charging constant current discharging was performed at a discharge current of 1 C until the battery voltage reached 2.5 V.
  • constant current discharging was performed at a discharge current of 0.33 C until the battery voltage reached 2.5 V. After the battery voltage reached 2.5 V, the battery was left to stand for 10 minutes. Next, constant current charging was performed at a charging current of 0.33 C until the battery voltage reached 4.25 V. After the battery voltage reached 4.25 V, constant voltage charging was performed until the current value decreased to 0.05 C. The battery was then left for 10 minutes. Thereafter, constant current discharging was performed at a discharging current of 0.33 C until the battery voltage reached 2.5 V.
  • LiFSI concentration after initial charge/discharge For the lithium ion secondary battery of each example after the initial charge and discharge, the LiFSI concentration after the initial charge and discharge was measured by the following method.
  • the lithium-ion secondary battery after initial charge and discharge in each example was decomposed in an inert gas atmosphere at a temperature of 25°C and a relative humidity of 3% or less.
  • 0.2 g of the electrolyte solution collected from the decomposed lithium-ion secondary battery was dissolved in 1.0 g of deuterated acetonitrile to prepare a first sample.
  • 0.002 g of hexafluorobenzene was added to the first sample as a reference material to prepare a second sample.
  • LiFSI concentration in the electrolyte (Amount of LiFSI in the first sample) / (Amount of electrolyte solution collected from the disassembled lithium-ion secondary battery) ⁇ 100
  • ⁇ Charge/discharge cycle> The lithium ion secondary battery was charged at 30 mA until the upper limit voltage reached 4.25 V. After the upper limit voltage of 4.25 V was reached, the lithium ion secondary battery was charged at a constant voltage until 2.5 hours had elapsed since the start of charging. The lithium ion secondary battery was then discharged at a constant current of 30 mA until the lower limit voltage of 2.5 V was reached.

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Abstract

A lithium ion secondary battery (10) provided with a positive electrode that includes a positive electrode active material layer (1), a negative electrode that includes a negative electrode active material layer (2), and an electrolyte, wherein: the negative electrode active material included in the negative electrode active material layer (2) has an SEI film on at least a portion of the surface thereof; the electrolyte contains lithium bis(fluorosulfonyl)imide; and the lithium bis(fluorosulfonyl)imide concentration in the electrolyte determined using a prescribed method is at least 0.6 mass%.

Description

リチウムイオン二次電池およびリチウムイオン二次電池モジュールLithium-ion secondary battery and lithium-ion secondary battery module

　本発明は、リチウムイオン二次電池およびリチウムイオン二次電池モジュールに関する。 The present invention relates to a lithium-ion secondary battery and a lithium-ion secondary battery module.

　リチウムイオン二次電池は、正極、負極、および電解液を含む。リチウムイオン二次電池に関する技術として、特許文献１および２に記載の技術がある。 A lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte. Patent Documents 1 and 2 describe technologies related to lithium-ion secondary batteries.

　特許文献１には、リチウム二次電池は様々な問題点を内包しているところ、そのうちの一部は、負極の製造及び作動特性と関連する問題点があるとして、正極活物質を含む正極合剤が集電体に塗布されている正極；負極活物質を含む負極合剤が集電体に塗布されている負極であって、炭素系材料及びケイ素系化合物を含む負極；及びリチウム塩及び非水系溶媒を含む電解液であって、前記電解液は環状カーボネート及び／又は線状溶媒を含む、電解質；を含むことを特徴とする二次電池を提供して、優れた寿命特性及び安全性を示すことが開示されている。 Patent Document 1 discloses that lithium secondary batteries have various inherent problems, some of which are related to the manufacturing and operating characteristics of the negative electrode, and discloses that it provides a secondary battery that exhibits excellent life characteristics and safety, comprising: a positive electrode in which a positive electrode mixture containing a positive electrode active material is applied to a current collector; a negative electrode in which a negative electrode mixture containing a negative electrode active material is applied to a current collector, the negative electrode including a carbon-based material and a silicon-based compound; and an electrolyte solution including a lithium salt and a non-aqueous solvent, the electrolyte solution including a cyclic carbonate and/or a linear solvent.

　特許文献２には、高容量であり、かつ充放電サイクル特性に優れたリチウムイオン二次電池を提供することを課題として、一般組成式ＬｉａＮｉ（１－ｂ－ｃ）ＣｏｂＭｃＯ２（ＭはＭｎおよびＡｌのうちの少なくとも１種の元素であり、０．９≦ａ≦１．３、０＜ｂ、０＜ｃ、ｂ＋ｃ≦０．５）で表されるリチウム含有複合酸化物を含有する正極と、ＳｉとＯとを構成元素に含む材料（ただし、Ｓｉに対するＯの原子比ｘは、０．５≦ｘ≦１．５である）と導電性材料との複合体、および前記複合体の含有する導電性材料以外の炭素材料を負極活物質として含有する負極と、Ｃ＝Ｃ二重結合を有する環状カーボネートと、ハロゲン置換された環状カーボネートとを含有する非水電解液とを備えており、初回充放電前後における負極活物質中の前記複合体の割合と非水電解液中の前記各環状カーボネートの含有量との関係を特定したリチウムイオン二次電池が開示されている。 Patent Document 2 aims to provide a lithium ion secondary battery that has high capacity and excellent charge-discharge cycle characteristics. The lithium ion secondary battery disclosed in Patent Document 2 includes a positive electrode containing a lithium-containing composite oxide represented by a general composition formula Li a Ni (1-bc) Co b M c O 2 (where M is at least one element selected from the group consisting of Mn and Al, and 0.9≦a≦1.3, 0<b, 0<c, and b+c≦0.5); a negative electrode containing, as a negative electrode active material, a composite of a material containing Si and O as constituent elements (wherein the atomic ratio x of O to Si is 0.5≦x≦1.5) and a conductive material, and a carbon material other than the conductive material contained in the composite; and a non-aqueous electrolyte containing a cyclic carbonate having a C═C double bond and a halogen-substituted cyclic carbonate, wherein the relationship between the proportion of the composite in the negative electrode active material and the content of each of the cyclic carbonates in the non-aqueous electrolyte before and after the initial charge and discharge is specified.

特開２０１８－８８４１９号公報JP 2018-88419 A 特開２０１１－２３３３６８号公報JP 2011-233368 A

　本発明は、サイクル特性が向上したリチウムイオン二次電池を提供するものである。 The present invention provides a lithium-ion secondary battery with improved cycle characteristics.

　本発明者らは、上記課題を達成するために鋭意検討を重ねた。その結果、本発明者らは、リチウムイオン二次電池内の電解液中のリチウムビス（フルオロスルホニル）イミドの濃度を特定の範囲にすることで、リチウムイオン二次電池のサイクル特性を向上できることを見出して、本発明を完成させた。 The inventors conducted extensive research to achieve the above-mentioned objectives. As a result, they discovered that the cycle characteristics of lithium ion secondary batteries can be improved by adjusting the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte solution within a specific range, and thus completed the present invention.

［１］
　正極活物質層を含む正極と、負極活物質層を含む負極と、電解液と、を含む、リチウムイオン二次電池であって、
　前記負極活物質層に含まれる負極活物質は、表面の少なくとも一部にＳＥＩ膜を有し、
　前記電解液は、リチウムビス（フルオロスルホニル）イミドを含み、
　下記＜方法１＞による、前記電解液中の前記リチウムビス（フルオロスルホニル）イミドの濃度は、０．６質量％以上である、リチウムイオン二次電池。
＜方法１＞
　前記リチウムイオン二次電池を不活性ガス雰囲気下で分解し、次いで、分解した前記リチウムイオン二次電池から採取した０．２ｇの前記電解液を、１．０ｇの重アセトニトリルに溶解させて第１サンプルを作製し、次いで、基準物質として０．００２ｇの六フッ化ベンゼンを前記第１サンプルに添加して第２サンプルを作製し、次いで、０．５ｇの前記第２サンプルを用いて、１９Ｆ－ＮＭＲ法により、前記第２サンプル中の前記リチウムビス（フルオロスルホニル）イミドの量を測定し、次いで、前記第２サンプル中の前記リチウムビス（フルオロスルホニル）イミドの量から前記第１サンプル中の前記リチウムビス（フルオロスルホニル）イミドの濃度を算出し、下記式（１）から前記電解液中の前記リチウムビス（フルオロスルホニル）イミドの濃度を算出する。
式（１）：前記電解液中の前記リチウムビス（フルオロスルホニル）イミドの濃度＝（前記第１サンプル中の前記リチウムビス（フルオロスルホニル）イミドの量）／（分解した前記リチウムイオン二次電池から採取した前記電解液の量）×１００
［２］
　前記負極活物質は、負極活物質（Ａ）と、前記負極活物質（Ａ）とは異なる種類の負極活物質（Ｂ）と、を含む、前記［１］に記載のリチウムイオン二次電池。
［３］
　前記負極活物質（Ａ）の、レーザー回折散乱法による体積基準のメジアン径Ｄ５０は、３．０μｍ以上３０．０μｍ以下であり、
　前記負極活物質（Ｂ）の、レーザー回折散乱法による体積基準のメジアン径Ｄ５０は、１．０μｍ以上２０．０μｍ以下である、前記［２］に記載のリチウムイオン二次電池。
［４］
　前記負極活物質（Ａ）は黒鉛粉末を含む、前記［２］または［３］に記載のリチウムイオン二次電池。
［５］
　前記黒鉛粉末は、黒鉛粉末（Ａ１）と、レーザー回折散乱法による体積基準のメジアン径Ｄ５０が前記黒鉛粉末（Ａ１）とは異なる黒鉛粉末（Ａ２）と、を含み、
　前記黒鉛粉末（Ａ１）のメジアン径Ｄ５０は、前記黒鉛粉末（Ａ２）のメジアン径Ｄ５０より大きい、前記［４］に記載のリチウムイオン二次電池。
［６］
　前記黒鉛粉末（Ａ１）は、表面に非晶質炭素を含む黒鉛粒子を含む、前記［５］に記載のリチウムイオン二次電池。
［７］
　前記黒鉛粉末（Ａ２）は、表面に非晶質炭素を含まない黒鉛粒子を含む、前記［５］または［６］に記載のリチウムイオン二次電池。
［８］
　前記黒鉛粉末（Ａ１）の前記メジアン径Ｄ５０は、５．０μｍ以上３０．０μｍ以下である、前記［５］～［７］のいずれかに記載のリチウムイオン二次電池。
［９］
　前記黒鉛粉末（Ａ２）の前記メジアン径Ｄ５０は、１．０μｍ以上２０．０μｍ以下である、前記［５］～［８］のいずれかに記載のリチウムイオン二次電池。
［１０］
　前記黒鉛粉末（Ａ１）のメジアン径Ｄ５０をＤ１、前記黒鉛粉末（Ａ２）のメジアン径Ｄ５０をＤ２とそれぞれしたときに、Ｄ１に対するＤ２の比Ｄ２／Ｄ１の値は、０．４０以上１．０未満である、前記［５］～［９］のいずれかに記載のリチウムイオン二次電池。
［１１］
　前記負極活物質（Ａ）中の前記黒鉛粉末（Ａ１）の含有量は、前記負極活物質（Ａ）中の前記黒鉛粉末（Ａ２）の含有量を１００質量部としたときに、５０質量部以上２００質量部以下である、前記［５］～［１０］のいずれかに記載のリチウムイオン二次電池。
［１２］
　前記負極活物質（Ｂ）は、酸化ケイ素粒子、並びにシリコンおよび炭素材料を含むＳｉ－Ｃ複合粒子からなる群から選択される一種または二種以上を含む、前記［２］～［１１］のいずれかに記載のリチウムイオン二次電池。
［１３］
　前記Ｓｉ－Ｃ複合粒子は、前記炭素材料が多孔質炭素材料を含み、かつ、前記シリコンが前記多孔質炭素材料の細孔内の少なくとも一部に存在する、前記［１２］に記載のリチウムイオン二次電池。
［１４］
　前記Ｓｉ－Ｃ複合粒子の、レーザー回折散乱法による体積基準のメジアン径Ｄ５０は、１．０μｍ以上１６．０μｍ以下である、前記［１２］または［１３］に記載のリチウムイオン二次電池。
［１５］
　前記負極活物質層中の前記負極活物質（Ａ）の含有量は、前記負極活物質層の全量を１００質量部としたときに、５０質量部以上９９質量部以下である、前記［２］～［１４］のいずれかに記載のリチウムイオン二次電池。
［１６］
　前記負極活物質層中の前記負極活物質（Ｂ）の含有量は、前記負極活物質層の全量を１００質量部としたときに、１質量部以上５０質量部以下である、前記［２］～［１５］のいずれかに記載のリチウムイオン二次電池。
［１７］
　前記負極活物質層中の前記負極活物質（Ａ）の含有量をＷＡ、前記負極活物質層中の前記負極活物質（Ｂ）の含有量をＷＢとそれぞれしたときに、ＷＢに対するＷＡの比ＷＡ／ＷＢの値は、１．０以上２０．０以下である、前記［２］～［１６］のいずれかに記載のリチウムイオン二次電池。
［１８］
　前記正極活物質層に含まれる正極活物質は、リチウム－ニッケル－コバルト－マンガン複合酸化物の単結晶により構成される粒子（Ｃ１）、およびリチウム－ニッケル－コバルト－マンガン複合酸化物の多結晶により構成される粒子（Ｃ２）から選択される一種または二種以上を含む粒子（Ｃ）を含む、前記［１］～［１７］のいずれかに記載のリチウムイオン二次電池。
［１９］
　前記粒子（Ｃ）中のニッケルの含有量は、ニッケル、コバルト、およびマンガンの含有量の合計を１００ｍｏｌとしたときに、８０ｍｏｌ以上である、前記［１８］に記載のリチウムイオン二次電池。
［２０］
　前記粒子（Ｃ）中のニッケル、コバルト、およびマンガンのそれぞれの含有量は、前記粒子（Ｃ）中のニッケル、コバルト、およびマンガンの含有量の合計を１００ｍｏｌとしたときに、ニッケルの含有量は８０ｍｏｌ以上９９ｍｏｌ以下であり、コバルトの含有量は０．５ｍｏｌ以上１０ｍｏｌ以下であり、かつマンガンの含有量は０．５ｍｏｌ以上１０ｍｏｌ以下である、前記［１８］または［１９］に記載のリチウムイオン二次電池。
［２１］
　下記の＜方法２＞による、２５℃での容量維持率Ｒ２５は、８７．０％以上である、前記［１］～［２０］のいずれかに記載のリチウムイオン二次電池。
＜方法２＞
　前記リチウムイオン二次電池を２５℃の恒温槽内に配置し、次いで、下記＜充放電サイクル＞によって前記リチウムイオン二次電池の充放電を行い、１回目の放電容量を測定し、次いで、下記＜充放電サイクル＞によって前記リチウムイオン二次電池の充放電を合計４９９回になるまで繰り返し、次いで、下記＜充放電サイクル＞によって前記リチウムイオン二次電池の充放電を行い、５００回目の放電容量を測定し、次いで、下記式（２）から前記容量維持率Ｒ２５を算出する。
式（２）：前記容量維持率Ｒ２５＝（前記５００回目の放電容量）／（前記１回目の放電容量）×１００
＜充放電サイクル＞
　上限電圧４．２５Ｖに達するまで３０ｍＡで前記リチウムイオン二次電池を充電し、次いで、前記上限電圧４．２５Ｖに達した後は、充電を開始してからの経過時間が２．５時間になるまで、前記リチウムイオン二次電池を定電圧で充電し、次いで、下限電圧２．５Ｖに達するまで３０ｍＡの定電流で前記リチウムイオン二次電池を放電する。
［２２］
　前記リチウムイオン二次電池中の前記電解液の含有量は、前記負極活物質の含有量と前記正極活物質層に含まれる正極活物質の含有量との合計を１００質量部としたときに、１５質量部以上６０質量部以下である、前記［１］～［２１］のいずれかに記載のリチウムイオン二次電池。
［２３］
　前記［１］～［２２］のいずれかに記載のリチウムイオン二次電池を備える、リチウムイオン二次電池モジュール。 [1]
A lithium ion secondary battery comprising: a positive electrode including a positive electrode active material layer; a negative electrode including a negative electrode active material layer; and an electrolyte solution,
the negative electrode active material contained in the negative electrode active material layer has an SEI film on at least a part of its surface,
the electrolyte solution contains lithium bis(fluorosulfonyl)imide;
A lithium ion secondary battery according to the following <Method 1>, wherein the concentration of the lithium bis(fluorosulfonyl)imide in the electrolyte solution is 0.6 mass % or more.
<Method 1>
The lithium ion secondary battery was disassembled under an inert gas atmosphere, and then 0.2 g of the electrolyte solution collected from the disassembled lithium ion secondary battery was dissolved in 1.0 g of deuterated acetonitrile to prepare a first sample. Next, 0.002 g of hexafluorobenzene was added to the first sample as a reference substance to prepare a second sample. Next, using 0.5 g of the second sample, the amount of lithium bis(fluorosulfonyl)imide in the second sample was measured by a 19 F-NMR method. Next, the concentration of lithium bis(fluorosulfonyl)imide in the first sample was calculated from the amount of lithium bis(fluorosulfonyl)imide in the second sample, and the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte solution was calculated using the following formula (1):
Equation (1): Concentration of the lithium bis(fluorosulfonyl)imide in the electrolyte solution=(Amount of the lithium bis(fluorosulfonyl)imide in the first sample)/(Amount of the electrolyte solution collected from the disassembled lithium ion secondary battery)×100
[2]
The lithium ion secondary battery according to [1], wherein the negative electrode active material includes a negative electrode active material (A) and a negative electrode active material (B) different from the negative electrode active material (A).
[3]
The negative electrode active material (A) has a volume-based median diameter D50 measured by a laser diffraction scattering method of 3.0 μm or more and 30.0 μm or less,
The lithium ion secondary battery according to [2], wherein the negative electrode active material (B) has a volume-based median diameter D 50 of 1.0 μm or more and 20.0 μm or less, as measured by a laser diffraction scattering method.
[4]
The lithium ion secondary battery according to [2] or [3], wherein the negative electrode active material (A) contains graphite powder.
[5]
The graphite powder comprises graphite powder (A1) and graphite powder (A2) having a volume-based median diameter D50 measured by a laser diffraction scattering method that is different from that of the graphite powder (A1),
The lithium ion secondary battery according to [4], wherein the median diameter D50 of the graphite powder (A1) is larger than the median diameter D50 of the graphite powder (A2).
[6]
The lithium ion secondary battery according to [5], wherein the graphite powder (A1) contains graphite particles containing amorphous carbon on the surface thereof.
[7]
The lithium ion secondary battery according to [5] or [6], wherein the graphite powder (A2) contains graphite particles whose surfaces do not contain amorphous carbon.
[8]
The lithium ion secondary battery according to any one of [5] to [7], wherein the median diameter D 50 of the graphite powder (A1) is 5.0 μm or more and 30.0 μm or less.
[9]
The lithium ion secondary battery according to any one of [5] to [8], wherein the median diameter D 50 of the graphite powder (A2) is 1.0 μm or more and 20.0 μm or less.
[10]
[9 ] The lithium ion secondary battery according to any one of the above [5] to [9], wherein when the median diameter D50 of the graphite powder (A1) is D1 and the median diameter D50 of the graphite powder (A2) is D2, the ratio D2/D1 of D2 to D1 is 0.40 or more and less than 1.0.
[11]
[11] The lithium ion secondary battery according to any one of [5] to [10], wherein the content of the graphite powder (A1) in the negative electrode active material (A) is 50 parts by mass or more and 200 parts by mass or less, when the content of the graphite powder (A2) in the negative electrode active material (A) is 100 parts by mass.
[12]
The lithium ion secondary battery according to any one of [2] to [11], wherein the negative electrode active material (B) comprises one or more selected from the group consisting of silicon oxide particles and Si—C composite particles containing silicon and a carbon material.
[13]
The lithium ion secondary battery according to [12], wherein the carbon material of the Si-C composite particles contains a porous carbon material, and the silicon is present in at least a portion of the pores of the porous carbon material.
[14]
The lithium ion secondary battery according to [12] or [13], wherein the Si—C composite particles have a volume-based median diameter D 50 of 1.0 μm or more and 16.0 μm or less, as measured by a laser diffraction scattering method.
[15]
[15] The lithium ion secondary battery according to any one of [2] to [14], wherein the content of the negative electrode active material (A) in the negative electrode active material layer is 50 parts by mass or more and 99 parts by mass or less, when the total amount of the negative electrode active material layer is 100 parts by mass.
[16]
[16]. The lithium ion secondary battery according to any one of [2] to [15], wherein the content of the negative electrode active material (B) in the negative electrode active material layer is 1 part by mass or more and 50 parts by mass or less, when the total amount of the negative electrode active material layer is 100 parts by mass.
[17]
The lithium ion secondary battery according to any one of [ 2 ] to [16], wherein when the content of the negative electrode active material (A) in the negative electrode active material layer is W A and the content of the negative electrode active material (B) in the negative electrode active material layer is W B , a ratio of W A to W B , W A /W B, is 1.0 or more and 20.0 or less.
[18]
The lithium ion secondary battery according to any one of [1] to [17], wherein the positive electrode active material contained in the positive electrode active material layer includes particles (C) including one or more kinds selected from particles (C1) constituted by a single crystal of a lithium-nickel-cobalt-manganese composite oxide and particles (C2) constituted by a polycrystal of a lithium-nickel-cobalt-manganese composite oxide.
[19]
The lithium ion secondary battery according to [18], wherein the content of nickel in the particles (C) is 80 mol or more when the total content of nickel, cobalt, and manganese is 100 mol.
[20]
The lithium ion secondary battery according to [18] or [19], wherein the contents of nickel, cobalt, and manganese in the particles (C) are such that, when the total content of nickel, cobalt, and manganese in the particles (C) is 100 mol, the content of nickel is 80 mol or more and 99 mol or less, the content of cobalt is 0.5 mol or more and 10 mol or less, and the content of manganese is 0.5 mol or more and 10 mol or less.
[21]
The lithium ion secondary battery according to any one of [1] to [20], wherein the capacity retention rate R 25 at 25° C. according to the following <Method 2> is 87.0% or more.
<Method 2>
The lithium ion secondary battery is placed in a thermostatic chamber at 25°C, and then the lithium ion secondary battery is charged and discharged in accordance with the <charge and discharge cycle> described below, and the first discharge capacity is measured. Next, the lithium ion secondary battery is repeatedly charged and discharged in accordance with the <charge and discharge cycle> described below until a total of 499 cycles have been reached. Next, the lithium ion secondary battery is charged and discharged in accordance with the <charge and discharge cycle> described below, and the discharge capacity is measured for the 500th cycle. Next, the capacity retention rate R25 is calculated using the following formula (2).
Formula (2): Capacity retention rate R 25 =(500th discharge capacity)/(1st discharge capacity)×100
<Charge/discharge cycle>
The lithium ion secondary battery is charged at 30 mA until an upper limit voltage of 4.25 V is reached, and then, after the upper limit voltage of 4.25 V is reached, the lithium ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging, and then, the lithium ion secondary battery is discharged at a constant current of 30 mA until a lower limit voltage of 2.5 V is reached.
[22]
The lithium ion secondary battery according to any one of [1] to [21], wherein the content of the electrolyte solution in the lithium ion secondary battery is 15 parts by mass or more and 60 parts by mass or less, when the total of the content of the negative electrode active material and the content of the positive electrode active material contained in the positive electrode active material layer is 100 parts by mass.
[23]
A lithium ion secondary battery module comprising the lithium ion secondary battery according to any one of [1] to [22].

　本発明によれば、サイクル特性が向上したリチウムイオン二次電池を提供できる。 The present invention provides a lithium-ion secondary battery with improved cycle characteristics.

本実施形態のリチウムイオン二次電池の一例を模式的に示す概略断面図である。1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery according to an embodiment of the present invention.

　以下、本発明の実施形態について、図面を参照しつつ、詳細に説明する。
　煩雑さを避けるため、同一図面内に同一の構成要素が複数ある場合には、その１つのみに符号を付し、全てには符号を付さない場合がある。
　図面はあくまで説明用のものである。図面中の各部材の形状や寸法比等は、必ずしも現実の物品と対応しない。
　本明細書における「ポリ（メタ）アクリル酸」の表記は、ポリアクリル酸とポリメタクリル酸の両方を包含する概念を表す。
　本実施形態の各成分について、それぞれ、一種を用いてもよいし、二種以上を組み合わせて用いてもよい。また、数値範囲を表す「～」は、以上、以下を表し、上限値および下限値をいずれも含む。
　本明細書におけるＳＯＣは、「Ｓｔａｔｅ　Ｏｆ　Ｃｈａｒｇｅ」を表す。
　本明細書における電流Ｃは、Ｃレートを表す。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
To avoid complexity, when there are a plurality of identical components in the same drawing, only one of them may be labeled with a reference symbol, and not all of them may be labeled with a reference symbol.
The drawings are for illustrative purposes only, and the shapes and dimensional ratios of the components in the drawings do not necessarily correspond to the actual products.
In this specification, the term "poly(meth)acrylic acid" represents a concept that includes both polyacrylic acid and polymethacrylic acid.
In the present embodiment, each of the components may be used alone or in combination of two or more. In addition, the symbol "to" indicating a numerical range means "at least" or "at most," and includes both the upper and lower limits.
In this specification, SOC stands for "State Of Charge."
The current C in this specification represents the C rate.

　以下、本発明を実施形態に基づいて説明する。 The present invention will be described below based on the embodiments.

（リチウムイオン二次電池）
　本実施形態において、リチウムイオン二次電池は、正極活物質層を含む正極と、負極活物質層を含む負極と、電解液と、を含む。本実施形態のリチウムイオン二次電池において、負極活物質層に含まれる負極活物質は、表面の少なくとも一部にＳＥＩ膜を有する。本実施形態のリチウムイオン二次電池において、電解液は、リチウムビス（フルオロスルホニル）イミドを含み、下記＜方法１＞による、電解液中のリチウムビス（フルオロスルホニル）イミドの濃度は、０．６質量％以上である。
＜方法１＞
　リチウムイオン二次電池を不活性ガス雰囲気下で分解する。次いで、分解したリチウムイオン二次電池から採取した０．２ｇの電解液を、１．０ｇの重アセトニトリルに溶解させて第１サンプルを作製する。次いで、基準物質として０．００２ｇの六フッ化ベンゼンを第１サンプルに添加して第２サンプルを作製する。次いで、０．５ｇの第２サンプルを用いて、１９Ｆ－ＮＭＲ法により、第２サンプル中のリチウムビス（フルオロスルホニル）イミドの量を測定する。次いで、第２サンプル中のリチウムビス（フルオロスルホニル）イミドの量から第１サンプル中のリチウムビス（フルオロスルホニル）イミドの濃度を算出する。次いで、下記式（１）から電解液中のリチウムビス（フルオロスルホニル）イミドの濃度を算出する。
式（１）：電解液中のリチウムビス（フルオロスルホニル）イミドの濃度＝（第１サンプル中のリチウムビス（フルオロスルホニル）イミドの量）／（分解したリチウムイオン二次電池から採取した電解液の量）×１００
　本実施形態のリチウムイオン二次電池は、上記のような構成を有することで、サイクル特性を向上できる。 (lithium ion secondary battery)
In this embodiment, the lithium ion secondary battery includes a positive electrode including a positive electrode active material layer, a negative electrode including a negative electrode active material layer, and an electrolyte. In this lithium ion secondary battery, the negative electrode active material included in the negative electrode active material layer has an SEI film on at least a portion of its surface. In this lithium ion secondary battery, the electrolyte includes lithium bis(fluorosulfonyl)imide, and the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.6 mass% or more according to the following <Method 1>.
<Method 1>
A lithium ion secondary battery is disassembled under an inert gas atmosphere. Next, 0.2 g of the electrolyte solution collected from the disassembled lithium ion secondary battery is dissolved in 1.0 g of deuterated acetonitrile to prepare a first sample. Next, 0.002 g of hexafluorobenzene is added to the first sample as a reference substance to prepare a second sample. Next, using 0.5 g of the second sample, the amount of lithium bis(fluorosulfonyl)imide in the second sample is measured by 19 F-NMR. Next, the concentration of lithium bis(fluorosulfonyl)imide in the first sample is calculated from the amount of lithium bis(fluorosulfonyl)imide in the second sample. Next, the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte solution is calculated using the following formula (1):
Equation (1): Concentration of lithium bis(fluorosulfonyl)imide in the electrolyte solution=(Amount of lithium bis(fluorosulfonyl)imide in the first sample)/(Amount of electrolyte solution collected from the disassembled lithium ion secondary battery)×100
The lithium ion secondary battery of this embodiment has the above-described configuration, and thus can improve cycle characteristics.

＜リチウムイオン二次電池の構成＞
　次に、本実施形態のリチウムイオン二次電池の構成について図を用いて説明する。図１は、本実施形態のリチウムイオン二次電池の一例を模式的に示す概略断面図である。
　本実施形態において、リチウムイオン二次電池１０は、正極活物質層１を含む正極と、負極活物質層２を含む負極と、電解液と、を含む。また、正極と負極との間にセパレータ５を設けることができる。正極と負極の電極対は複数設けることができる。 <Configuration of lithium-ion secondary battery>
Next, the configuration of the lithium ion secondary battery of this embodiment will be described with reference to the drawings. Figure 1 is a schematic cross-sectional view showing an example of the lithium ion secondary battery of this embodiment.
In this embodiment, the lithium ion secondary battery 10 includes a positive electrode including a positive electrode active material layer 1, a negative electrode including a negative electrode active material layer 2, and an electrolyte. A separator 5 may be provided between the positive electrode and the negative electrode. A plurality of electrode pairs of a positive electrode and a negative electrode may be provided.

　リチウムイオン二次電池１０は、正極集電体３と、その上に設けられた正極活物質を含む正極活物質層１とを含む正極を有している。また、リチウムイオン二次電池１０は、負極集電体４と、その上に設けられた負極活物質を含む負極活物質層２とを含む負極を有している。正極および負極は、例えば、正極活物質層１と負極活物質層２とが対向するように、セパレータ５を介して積層されている。正極および負極からなる電極対は、外装体６および外装体７で形成された容器内に収容されている。正極集電体３には正極タブ９が接続されており、負極集電体４には負極タブ８が接続されている。正極タブ９および負極タブ８は容器の外に引き出されている。容器内には、注入された電解液が封止されている。容器内には、複数の電極対が積層された電極群が収容されていてもよい。 The lithium-ion secondary battery 10 has a positive electrode including a positive electrode current collector 3 and a positive electrode active material layer 1 containing a positive electrode active material provided thereon. The lithium-ion secondary battery 10 also has a negative electrode including a negative electrode current collector 4 and a negative electrode active material layer 2 containing a negative electrode active material provided thereon. The positive electrode and negative electrode are stacked, for example, with a separator 5 interposed between them, so that the positive electrode active material layer 1 and the negative electrode active material layer 2 face each other. The electrode pair consisting of the positive electrode and the negative electrode is housed in a container formed by an outer casing 6 and an outer casing 7. A positive electrode tab 9 is connected to the positive electrode current collector 3, and a negative electrode tab 8 is connected to the negative electrode current collector 4. The positive electrode tab 9 and the negative electrode tab 8 are extended outside the container. An electrolyte solution is injected and sealed inside the container. The container may also house an electrode group consisting of multiple electrode pairs stacked together.

＜リチウムイオン二次電池の製造方法＞
　本実施形態において、リチウムイオン二次電池は公知の方法に準じて作製することができる。電極は、例えば、積層体や捲回体が使用できる。外装体としては、金属外装体やアルミラミネート外装体が適宜使用できる。電池の形状は、ラミネート型、コイン型、ボタン型、シート型、円筒型、角型、扁平型等いずれの形状であってもよいが、ラミネート型の電池が好ましい。 <Method of manufacturing lithium-ion secondary battery>
In this embodiment, the lithium ion secondary battery can be fabricated according to a known method. The electrode can be, for example, a laminate or a wound body. The exterior can be a metal exterior or an aluminum laminate exterior. The battery may have any shape, such as a laminate, coin, button, sheet, cylindrical, rectangular, or flat shape, but a laminate battery is preferred.

　次に、リチウムイオン二次電池を構成ごとに分けて説明する。 Next, we will explain lithium-ion secondary batteries by their structure.

＜電解液＞
　本実施形態のリチウムイオン二次電池において、電解液は、電解質、および有機溶媒を含む。本実施形態のリチウムイオン二次電池において、電解液は電解質としてリチウムビス（フルオロスルホニル）イミド（以下、ＬｉＦＳＩとも呼ぶ。）を含む。 <Electrolyte>
In the lithium ion secondary battery of this embodiment, the electrolytic solution contains an electrolyte and an organic solvent. In the lithium ion secondary battery of this embodiment, the electrolytic solution contains lithium bis(fluorosulfonyl)imide (hereinafter also referred to as LiFSI) as the electrolyte.

　本実施形態のリチウムイオン二次電池において、ＬｉＦＳＩ以外の電解質は、例えば、六フッ化リン酸リチウム（ＬｉＰＦ６）、ジフルオロビス（オキサラト）リン酸リチウム（ＬｉＤＯＤＦＰ）、ジフルオロリン酸リチウム（ＬｉＰＯ２Ｆ２）、ＬｉＣｌＯ４、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、ＬｉＣＦ３ＣＯ２、ＬｉＡｓＦ６、ＬｉＳｂＦ６、ＬｉＢ１０Ｃｌ１０、ＬｉＡｌＣｌ４、ＬｉＣｌ、ＬｉＢｒ、ＬｉＢ（Ｃ２Ｈ５）４、ＣＨ３ＳＯ３Ｌｉ、ＬｉＣ４Ｆ９ＳＯ３、Ｌｉ（ＣＦ３ＳＯ２）２Ｎ、低級脂肪酸のリチウム塩、および低級カルボン酸のリチウム塩からなる群から選択される一種または二種以上を含み、好ましくはＬｉＰＦ６およびＬｉＣｌからなる群から選択される一種または二種以上を含み、より好ましくはＬｉＰＦ６を含む。 In the lithium ion secondary battery of this embodiment, examples of electrolytes other than LiFSI include lithium hexafluorophosphate (LiPF 6 ), lithium difluorobis(oxalato)phosphate (LiDODFP), lithium difluorophosphate (LiPO 2 F 2 ), LiClO 4 , LiBF 4 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiB 10 Cl 10 , LiAlCl 4 , LiCl, LiBr, LiB(C 2 H 5 ) 4 , CH 3 SO 3 Li, LiC 4 F 9 SO 3 , and Li(CF 3 SO 2 ) 2 . The lithium salt of a lower fatty acid, a lower carboxylic acid, or a mixture thereof may contain one or more compounds selected from the group consisting of N, a lithium salt of a lower fatty acid, and a lithium salt of a lower carboxylic acid, and preferably contains one or more compounds selected from the group consisting of LiPF6 and LiCl, and more preferably contains LiPF6 .

　本実施形態のリチウムイオン二次電池において、有機溶媒は、電解質を溶解させることができるものであれば特に限定されない。有機溶媒は、例えば、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）、ビニレンカーボネート（ＶＣ）等のカーボネート類；γ－ブチロラクトン、γ－バレロラクトン等のラクトン類；トリメトキシメタン、１，２－ジメトキシエタン、ジエチルエーテル、２－エトキシエタン、テトラヒドロフラン、２－メチルテトラヒドロフラン等のエーテル類；ジメチルスルホキシド等のスルホキシド類；１，３－ジオキソラン、４－メチル－１，３－ジオキソラン等のオキソラン類；アセトニトリル、ニトロメタン、ホルムアミド、ジメチルホルムアミド等の含窒素類；ギ酸メチル、酢酸メチル、酢酸エチル、酢酸ブチル、プロピオン酸メチル、プロピオン酸エチル等の有機酸エステル類；リン酸トリエステル等のリン酸エステル類；ジグライム類；トリグライム類；スルホラン、メチルスルホラン等のスルホラン類；３－メチル－２－オキサゾリジノン等のオキサゾリジノン類；および１，３－プロパンスルトン、１，４－ブタンスルトン、ナフタスルトン等のスルトン類からなる群から選択される一種または二種以上を含み、好ましくはカーボネート類を含み、より好ましくはＥＣおよびＥＭＣからなる群から選択される一種または二種以上を含む。 In the lithium-ion secondary battery of this embodiment, the organic solvent is not particularly limited as long as it can dissolve the electrolyte. Examples of organic solvents include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC); lactones such as γ-butyrolactone and γ-valerolactone; ethers such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide; oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; and acetonitrile. The solvent contains one or more solvents selected from the group consisting of nitrogen-containing solvents such as nitromethane, formamide, and dimethylformamide; organic acid esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and ethyl propionate; phosphate esters such as phosphate triesters; diglymes; triglymes; sulfolanes such as sulfolane and methylsulfolane; oxazolidinones such as 3-methyl-2-oxazolidinone; and sultones such as 1,3-propane sultone, 1,4-butane sultone, and naphtha sultone, preferably carbonates, and more preferably one or more solvents selected from the group consisting of EC and EMC.

　本実施形態のリチウムイオン二次電池において、電解液は添加剤をさらに含んでもよい。添加剤としては、例えば、フルオロエチレンカーボネート（ＦＥＣ）、ビニレンカーボネート（ＶＣ）、およびエチレンサルファイト（ＥＳ）からなる群から選択される一種または二種以上が挙げられる。 In the lithium-ion secondary battery of this embodiment, the electrolyte may further contain an additive. Examples of the additive include one or more selected from the group consisting of fluoroethylene carbonate (FEC), vinylene carbonate (VC), and ethylene sulfite (ES).

　本実施形態のリチウムイオン二次電池において、リチウムイオン二次電池作製時の電解液中のＬｉＦＳＩの濃度（以下、ＬｉＦＳＩ濃度（作製時）とも呼ぶ。）は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは０．７質量％以上４．８質量％以下、より好ましくは０．８質量％以上４．５質量％以下、さらに好ましくは０．９質量％以上４．０質量％以下、さらに好ましくは１．０質量％以上３．５質量％以下、さらに好ましくは１．０質量％以上３．２質量％以下である。 In the lithium ion secondary battery of this embodiment, the concentration of LiFSI in the electrolyte during production of the lithium ion secondary battery (hereinafter also referred to as LiFSI concentration (at production)) is preferably 0.7% by mass or more and 4.8% by mass or less, more preferably 0.8% by mass or more and 4.5% by mass or less, even more preferably 0.9% by mass or more and 4.0% by mass or less, even more preferably 1.0% by mass or more and 3.5% by mass or less, and even more preferably 1.0% by mass or more and 3.2% by mass or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態のリチウムイオン二次電池において、リチウムイオン二次電池作製時の電解液中のＬｉＰＦ６の濃度（以下、ＬｉＰＦ６濃度（作製時）とも呼ぶ。）は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは１．０質量％以上、より好ましくは５．０質量％以上、さらに好ましくは１０．０質量％以上、さらに好ましくは１０．５質量％以上、さらに好ましくは１１．０質量％以上、さらに好ましくは１１．５質量％以上である。 In the lithium ion secondary battery of this embodiment, the concentration of LiPF6 in the electrolyte solution during production of the lithium ion secondary battery (hereinafter also referred to as LiPF6 concentration (at production)) is preferably 1.0 mass% or more, more preferably 5.0 mass% or more, even more preferably 10.0 mass% or more, still more preferably 10.5 mass% or more, still more preferably 11.0 mass% or more, and still more preferably 11.5 mass% or more, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態のリチウムイオン二次電池において、ＬｉＰＦ６濃度（作製時）は、電池部材の腐食を低減できる観点から、好ましくは２０．０質量％以下、より好ましくは１８．０質量％以下、さらに好ましくは１５．０質量％以下、さらに好ましくは１４．０質量％以下、さらに好ましくは１３．０質量％以下、さらに好ましくは１２．５質量％以下である。 In the lithium ion secondary battery of this embodiment, the LiPF6 concentration (at the time of manufacture) is preferably 20.0 mass % or less, more preferably 18.0 mass % or less, even more preferably 15.0 mass % or less, still more preferably 14.0 mass % or less, still more preferably 13.0 mass % or less, and still more preferably 12.5 mass % or less, from the viewpoint of reducing corrosion of the battery components.

　本実施形態のリチウムイオン二次電池において、ＬｉＰＦ６濃度（作製時）は、リチウムイオン二次電池のサイクル特性をより向上できる観点および電池部材の腐食を低減できる観点から、好ましくは１．０質量％以上２０．０質量％以下、より好ましくは５．０質量％以上１８．０質量％以下、さらに好ましくは１０．０質量％以上１５．０質量％以下、さらに好ましくは１０．５質量％以上１４．０質量％以下、さらに好ましくは１１．０質量％以上１３．０質量％以下、さらに好ましくは１１．５質量％以上１２．５質量％以下である。 In the lithium ion secondary battery of this embodiment, the LiPF6 concentration (at the time of production) is preferably 1.0 mass % or more and 20.0 mass % or less, more preferably 5.0 mass % or more and 18.0 mass % or less, even more preferably 10.0 mass % or more and 15.0 mass % or less, still more preferably 10.5 mass % or more and 14.0 mass % or less, still more preferably 11.0 mass % or more and 13.0 mass % or less, and still more preferably 11.5 mass % or more and 12.5 mass % or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery and reducing corrosion of the battery components.

　本実施形態のリチウムイオン二次電池において、リチウムイオン二次電池中の電解液の含有量は、リチウムイオン二次電池中の負極活物質の含有量と正極活物質の含有量との合計を１００質量部としたときに、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは１５質量部以上６０質量部以下、より好ましくは２０質量部以上５５質量部以下、さらに好ましくは２５質量部以上５０質量部以下、さらに好ましくは３０質量部以上４５質量部以下である。 In the lithium ion secondary battery of this embodiment, the content of the electrolyte in the lithium ion secondary battery is preferably 15 parts by mass or more and 60 parts by mass or less, more preferably 20 parts by mass or more and 55 parts by mass or less, even more preferably 25 parts by mass or more and 50 parts by mass or less, and even more preferably 30 parts by mass or more and 45 parts by mass or less, when the total content of the negative electrode active material and the positive electrode active material in the lithium ion secondary battery is taken as 100 parts by mass, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

＜負極＞
　本実施形態の負極は、負極活物質層を含む。本実施形態の負極は、リチウムイオン二次電池の電池性能をより向上できる観点から、好ましくは、負極集電体と本実施形態の負極活物質層とを備える。 <Negative electrode>
The negative electrode of this embodiment includes a negative electrode active material layer. From the viewpoint of further improving the battery performance of the lithium ion secondary battery, the negative electrode of this embodiment preferably includes a negative electrode current collector and the negative electrode active material layer of this embodiment.

　本実施形態のリチウムイオン二次電池において、負極活物質層に含まれる負極活物質は、表面の少なくとも一部にＳＥＩ（Ｓｏｌｉｄ　Ｅｌｅｃｔｒｏｌｙｔｅ　Ｉｎｔｅｒｐｈａｓｅ）膜を有し、好ましくは表面の全体にＳＥＩ膜を有する。
　一般的に、ＳＥＩ膜は、初期充放電時に、負極の表面で電解液が分解されることによって形成される。具体的には、ＳＥＩ膜は、電解液および電解液の添加剤の分解物等によって、負極活物質の表面の少なくとも一部に形成される膜である。ＳＥＩ膜は、リチウムイオンを負極中に挿入または負極中から脱離させる役割を果たしつつ、負極の表面で電解液がさらに分解されることを低減する役割を果たす。 In the lithium ion secondary battery of this embodiment, the negative electrode active material contained in the negative electrode active material layer has an SEI (Solid Electrolyte Interphase) film on at least a part of its surface, and preferably has an SEI film on its entire surface.
Generally, the SEI film is formed by decomposition of the electrolyte on the surface of the negative electrode during initial charge/discharge. Specifically, the SEI film is a film formed on at least a portion of the surface of the negative electrode active material by decomposition products of the electrolyte and electrolyte additives. The SEI film functions to insert or extract lithium ions into or from the negative electrode, while also functioning to reduce further decomposition of the electrolyte on the surface of the negative electrode.

　例えば、実施例に記載の＜リチウムイオン二次電池の初期充放電＞の方法によって、負極（負極活物質）の表面の少なくとも一部に、ＳＥＩ膜を形成できる。すなわち、本実施形態のリチウムイオン二次電池は、負極活物質層に含まれる負極活物質の表面の少なくとも一部にＳＥＩ膜を有するため、少なくとも初期充放電を行った後のリチウムイオン二次電池である。 For example, an SEI film can be formed on at least a portion of the surface of the negative electrode (negative electrode active material) by the method described in the "Initial Charging and Discharging of Lithium-Ion Secondary Battery" section in the Examples. In other words, the lithium-ion secondary battery of this embodiment has an SEI film on at least a portion of the surface of the negative electrode active material contained in the negative electrode active material layer, and is therefore a lithium-ion secondary battery after at least initial charging and discharging.

＜負極活物質層＞
　本実施形態の負極活物質層は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは、本実施形態の負極活物質およびバインダーを含み、より好ましくは、本実施形態の負極活物質、バインダーおよび導電助剤を含む。 <Negative electrode active material layer>
From the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery, the negative electrode active material layer of the present embodiment preferably contains the negative electrode active material of the present embodiment and a binder, and more preferably contains the negative electrode active material of the present embodiment, a binder, and a conductive additive.

　本実施形態の負極活物質層の厚みは、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは１０μｍ以上２５０μｍ以下、より好ましくは１５μｍ以上２００μｍ以下、さらに好ましくは２０μｍ以上１００μｍ以下、さらに好ましくは２５μｍ以上７５μｍ以下である。 In order to further improve the cycle characteristics of the lithium-ion secondary battery, the thickness of the negative electrode active material layer in this embodiment is preferably 10 μm or more and 250 μm or less, more preferably 15 μm or more and 200 μm or less, even more preferably 20 μm or more and 100 μm or less, and even more preferably 25 μm or more and 75 μm or less.

　本実施形態の負極活物質層の密度は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは０．５０ｇ／ｃｍ３以上３．００ｇ／ｃｍ３以下、より好ましくは１．００ｇ／ｃｍ３以上２．５０ｇ／ｃｍ３以下、さらに好ましくは１．３０ｇ／ｃｍ３以上２．００ｇ／ｃｍ３以下である。 From the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery, the density of the negative electrode active material layer of this embodiment is preferably 0.50 g/ cm3 or more and 3.00 g/ cm3 or less, more preferably 1.00 g/ cm3 or more and 2.50 g/cm3 or less , and even more preferably 1.30 g/ cm3 or more and 2.00 g/ cm3 or less.

＜負極活物質＞
　本実施形態の負極活物質は、好ましくは、炭素材料、リチウム系金属材料、Ｓｉ系材料および導電性ポリマー材料からなる群より選択される一種または二種以上を含み、より好ましくは炭素材料およびＳｉ系材料からなる群より選択される一種または二種以上を含み、さらに好ましくは炭素材料およびＳｉ系材料の両方を含む。
　本実施形態の炭素材料は、例えば、黒鉛粉末、ハードカーボン、ソフトカーボンまたはこれらの任意の混合物等が挙げられ、好ましくは黒鉛粉末を含む。
　本実施形態のＳｉ系材料は、例えば、酸化ケイ素粒子、並びにシリコンおよび炭素材料を含むＳｉ－Ｃ複合粒子（以下、Ｓｉ－Ｃ複合粒子とも呼ぶ。）等が挙げられ、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくはＳｉ－Ｃ複合粒子を含む。 <Negative electrode active material>
The negative electrode active material of the present embodiment preferably contains one or more materials selected from the group consisting of a carbon material, a lithium-based metal material, a Si-based material, and a conductive polymer material, more preferably contains one or more materials selected from the group consisting of a carbon material and a Si-based material, and even more preferably contains both a carbon material and a Si-based material.
Examples of the carbon material of the present embodiment include graphite powder, hard carbon, soft carbon, and any mixture thereof, and graphite powder is preferred.
Examples of the Si-based material of the present embodiment include silicon oxide particles and Si-C composite particles containing silicon and a carbon material (hereinafter also referred to as Si-C composite particles), and preferably contains Si-C composite particles from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態の負極活物質層中の負極活物質の含有量は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、負極活物質層の全量を１００．０質量部としたとき、好ましくは５０．０質量部以上１００．０質量部以下、より好ましくは７５．０質量部以上９９．０質量部以下、さらに好ましくは８５．０質量部以上９８．５質量部以下、さらに好ましくは９０．０質量部以上９８．０質量部以下、さらに好ましくは９５．０質量部以上９７．５質量部以下である。 In order to further improve the cycle characteristics of the lithium-ion secondary battery, the content of the negative electrode active material in the negative electrode active material layer of this embodiment, when the total amount of the negative electrode active material layer is taken as 100.0 parts by mass, is preferably 50.0 parts by mass or more and 100.0 parts by mass or less, more preferably 75.0 parts by mass or more and 99.0 parts by mass or less, even more preferably 85.0 parts by mass or more and 98.5 parts by mass or less, even more preferably 90.0 parts by mass or more and 98.0 parts by mass or less, and even more preferably 95.0 parts by mass or more and 97.5 parts by mass or less.

　本実施形態のリチウムイオン二次電池において、本実施形態の負極活物質は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは負極活物質（Ａ）と、負極活物質（Ａ）とは異なる種類の負極活物質（Ｂ）と、を含む。 In the lithium ion secondary battery of this embodiment, the negative electrode active material of this embodiment preferably includes a negative electrode active material (A) and a negative electrode active material (B) of a type different from the negative electrode active material (A), from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

＜負極活物質（Ａ）＞
　本実施形態のリチウムイオン二次電池において、負極活物質（Ａ）は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは炭素材料を含み、より好ましくは黒鉛粉末を含む。 <Negative electrode active material (A)>
In the lithium ion secondary battery of this embodiment, the negative electrode active material (A) preferably contains a carbon material, more preferably contains graphite powder, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態のリチウムイオン二次電池において、負極活物質（Ａ）の、レーザー回折散乱法による体積基準のメジアン径Ｄ５０は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは３．０μｍ以上３０．０μｍ以下、より好ましくは５．０μｍ以上２７．５μｍ以下、さらに好ましくは７．５μｍ以上２２．５μｍ以下、さらに好ましくは８．０μｍ以上１５．５μｍ以下、さらに好ましくは９．０μｍ以上１２．０μｍ以下である。 In the lithium ion secondary battery of this embodiment, the volume-based median diameter D50 of the negative electrode active material (A) as measured by a laser diffraction scattering method is preferably 3.0 μm or more and 30.0 μm or less, more preferably 5.0 μm or more and 27.5 μm or less, even more preferably 7.5 μm or more and 22.5 μm or less, still more preferably 8.0 μm or more and 15.5 μm or less, and still more preferably 9.0 μm or more and 12.0 μm or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態の黒鉛粉末は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは、黒鉛粉末（Ａ１）と、黒鉛粉末（Ａ１）とは異なる種類の黒鉛粉末（Ａ１’）と、を含む。本実施形態の黒鉛粉末は、より好ましくは、黒鉛粉末（Ａ１）と、レーザー回折散乱法による体積基準のメジアン径Ｄ５０が黒鉛粉末（Ａ１）とは異なる黒鉛粉末（Ａ２）と、を含み、黒鉛粉末（Ａ１）のメジアン径Ｄ５０は、黒鉛粉末（Ａ２）のメジアン径Ｄ５０より大きい。 From the viewpoint of further improving the cycle characteristics of a lithium ion secondary battery, the graphite powder of this embodiment preferably contains graphite powder (A1) and a type of graphite powder (A1') different from the graphite powder (A1). The graphite powder of this embodiment more preferably contains graphite powder (A1) and graphite powder (A2) having a volume-based median diameter D50 measured by a laser diffraction scattering method different from that of the graphite powder (A1), and the median diameter D50 of the graphite powder (A1) is larger than the median diameter D50 of the graphite powder (A2).

　黒鉛粉末（Ａ１）は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは表面に非晶質炭素を含む黒鉛粒子を含み、より好ましくは表面に非晶質炭素を含む人造黒鉛粒子を含む。 From the viewpoint of further improving the cycle characteristics of lithium ion secondary batteries, the graphite powder (A1) preferably contains graphite particles containing amorphous carbon on the surface, and more preferably contains artificial graphite particles containing amorphous carbon on the surface.

　黒鉛粉末（Ａ２）は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは表面に非晶質炭素を含まない黒鉛粒子を含み、より好ましくは表面に非晶質炭素を含まない人造黒鉛粒子を含む。 From the viewpoint of further improving the cycle characteristics of lithium ion secondary batteries, the graphite powder (A2) preferably contains graphite particles that do not contain amorphous carbon on the surface, and more preferably contains artificial graphite particles that do not contain amorphous carbon on the surface.

　黒鉛粉末（Ａ１’）は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは表面に非晶質炭素を含まない黒鉛粒子を含み、より好ましくは表面に非晶質炭素を含まない人造黒鉛粒子を含む。黒鉛粉末（Ａ１’）は、黒鉛粉末（Ａ２）を含んでもよい。 From the viewpoint of further improving the cycle characteristics of lithium-ion secondary batteries, the graphite powder (A1') preferably contains graphite particles that do not contain amorphous carbon on their surfaces, and more preferably contains artificial graphite particles that do not contain amorphous carbon on their surfaces. Graphite powder (A1') may also contain graphite powder (A2).

　本実施形態のリチウムイオン二次電池において、黒鉛粉末（Ａ１）のレーザー回折散乱法による体積基準のメジアン径Ｄ５０は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは５．０μｍ以上３０．０μｍ以下、より好ましくは６．０μｍ以上２７．５μｍ以下、さらに好ましくは７．５μｍ以上２５．０μｍ以下、さらに好ましくは９．０μｍ以上２０．０μｍ以下、さらに好ましくは１１．０μｍ以上１８．０μｍ以下、さらに好ましくは１２．０μｍ以上１６．０μｍ以下である。 In the lithium ion secondary battery of this embodiment, the volume-based median diameter D50 of the graphite powder (A1) measured by a laser diffraction scattering method is preferably 5.0 μm or more and 30.0 μm or less, more preferably 6.0 μm or more and 27.5 μm or less, even more preferably 7.5 μm or more and 25.0 μm or less, still more preferably 9.0 μm or more and 20.0 μm or less, still more preferably 11.0 μm or more and 18.0 μm or less, and still more preferably 12.0 μm or more and 16.0 μm or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態のリチウムイオン二次電池において、黒鉛粉末（Ａ２）のレーザー回折散乱法による体積基準のメジアン径Ｄ５０は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは１．０μｍ以上２０．０μｍ以下、より好ましくは３．０μｍ以上１８．０μｍ以下、さらに好ましくは５．０μｍ以上１７．０μｍ以下、さらに好ましくは７．０μｍ以上１５．０μｍ以下、さらに好ましくは７．５μｍ以上１３．０μｍ以下、さらに好ましくは８．０μｍ以上１２．０μｍ以下である。 In the lithium ion secondary battery of this embodiment, the volume-based median diameter D50 of the graphite powder (A2) measured by a laser diffraction scattering method is preferably 1.0 μm or more and 20.0 μm or less, more preferably 3.0 μm or more and 18.0 μm or less, even more preferably 5.0 μm or more and 17.0 μm or less, still more preferably 7.0 μm or more and 15.0 μm or less, still more preferably 7.5 μm or more and 13.0 μm or less, and still more preferably 8.0 μm or more and 12.0 μm or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態のリチウムイオン二次電池において、黒鉛粉末（Ａ１）のメジアン径Ｄ５０をＤ１、黒鉛粉末（Ａ２）のメジアン径Ｄ５０をＤ２とそれぞれしたときに、Ｄ１に対するＤ２の比Ｄ２／Ｄ１の値は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは０．４０以上１．０未満、より好ましくは０．４５以上０．９０以下、さらに好ましくは０．５０以上０．８０以下、さらに好ましくは０．５５以上０．７５以下、さらに好ましくは０．６０以上０．７０以下である。 In the lithium ion secondary battery of this embodiment, when the median diameter D50 of the graphite powder (A1) is D1 and the median diameter D50 of the graphite powder (A2) is D2 , the ratio of D2 to D1 , D2 / D1 , is preferably 0.40 or more and less than 1.0, more preferably 0.45 or more and 0.90 or less, even more preferably 0.50 or more and 0.80 or less, even more preferably 0.55 or more and 0.75 or less, and still more preferably 0.60 or more and 0.70 or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態のリチウムイオン二次電池において、負極活物質（Ａ）中の黒鉛粉末（Ａ１）の含有量は、負極活物質（Ａ）中の黒鉛粉末（Ａ２）の含有量を１００質量部としたときに、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは５０質量部以上２００質量部以下、より好ましくは６０質量部以上１６０質量部以下、さらに好ましくは７０質量部以上１４０質量部以下、さらに好ましくは８０質量部以上１２０質量部以下、さらに好ましくは９０質量部以上１１０質量部以下である。 In the lithium ion secondary battery of this embodiment, the content of graphite powder (A1) in the negative electrode active material (A) is preferably 50 parts by mass or more and 200 parts by mass or less, more preferably 60 parts by mass or more and 160 parts by mass or less, even more preferably 70 parts by mass or more and 140 parts by mass or less, even more preferably 80 parts by mass or more and 120 parts by mass or less, and even more preferably 90 parts by mass or more and 110 parts by mass or less, when the content of graphite powder (A2) in the negative electrode active material (A) is taken as 100 parts by mass, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態のリチウムイオン二次電池において、負極活物質層中の負極活物質（Ａ）の含有量は、負極活物質層の全量を１００質量部としたときに、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは５０質量部以上９９質量部以下、より好ましくは６０質量部以上９５質量部以下、さらに好ましくは６５質量部以上９０質量部以下、さらに好ましくは６８質量部以上８５質量部以下、さらに好ましくは７０質量部以上８０質量部以下である。 In the lithium ion secondary battery of this embodiment, the content of the negative electrode active material (A) in the negative electrode active material layer, when the total amount of the negative electrode active material layer is taken as 100 parts by mass, is preferably 50 parts by mass or more and 99 parts by mass or less, more preferably 60 parts by mass or more and 95 parts by mass or less, even more preferably 65 parts by mass or more and 90 parts by mass or less, even more preferably 68 parts by mass or more and 85 parts by mass or less, and even more preferably 70 parts by mass or more and 80 parts by mass or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

＜負極活物質（Ｂ）＞
　本実施形態のリチウムイオン二次電池において、負極活物質（Ｂ）は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくはＳｉ系材料を含み、より好ましくはＳｉ／Ｃ粉末を含む。Ｓｉ／Ｃ粉末は、後述する、酸化ケイ素粒子、並びにシリコンおよび炭素材料を含むＳｉ－Ｃ複合粒子からなる群から選択される一種または二種以上を含んでもよい。 <Negative electrode active material (B)>
In the lithium ion secondary battery of this embodiment, the negative electrode active material (B) preferably contains a Si-based material, more preferably a Si/C powder, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery. The Si/C powder may contain one or more kinds selected from the group consisting of silicon oxide particles and Si-C composite particles containing silicon and a carbon material, as described below.

　本実施形態のリチウムイオン二次電池において、負極活物質（Ｂ）の、レーザー回折散乱法による体積基準のメジアン径Ｄ５０は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは１．０μｍ以上２０．０μｍ以下、より好ましくは１．５μｍ以上１９．０μｍ以下、さらに好ましくは２．５μｍ以上１７．０μｍ以下、さらに好ましくは３．５μｍ以上１１．０μｍ以下、さらに好ましくは４．０μｍ以上９．０μｍ以下である。 In the lithium ion secondary battery of this embodiment, the volume-based median diameter D50 of the negative electrode active material (B) as measured by a laser diffraction scattering method is preferably 1.0 μm or more and 20.0 μm or less, more preferably 1.5 μm or more and 19.0 μm or less, even more preferably 2.5 μm or more and 17.0 μm or less, even more preferably 3.5 μm or more and 11.0 μm or less, and still more preferably 4.0 μm or more and 9.0 μm or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態のリチウムイオン二次電池において、負極活物質（Ｂ）は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくはＳｉ系材料を含み、より好ましくは酸化ケイ素粒子、並びにシリコンおよび炭素材料を含むＳｉ－Ｃ複合粒子からなる群から選択される一種または二種以上を含み、さらに好ましくはＳｉ－Ｃ複合粒子を含む。 In the lithium ion secondary battery of this embodiment, the negative electrode active material (B) preferably contains a Si-based material, more preferably contains one or more types selected from the group consisting of silicon oxide particles and Si-C composite particles containing silicon and a carbon material, and even more preferably contains Si-C composite particles, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　Ｓｉ－Ｃ複合粒子は、炭素材料が多孔質炭素材料を含み、かつ、シリコンが多孔質炭素材料の細孔内の少なくとも一部に存在する粒子である。 Si-C composite particles are particles in which the carbon material contains a porous carbon material and silicon is present at least partially within the pores of the porous carbon material.

　Ｓｉ－Ｃ複合粒子を構成する多孔質炭素材料の例としては、活性炭、炭素繊維の凝集体やカーボンナノチューブの凝集体、樹脂や有機物を熱処理して得られる炭素、ハードカーボンなどが挙げられる。多孔質炭素材料は活性炭の製造方法や、ポリマーへの熱処理による公知の製造方法で生成できるが、市販されているものを購入してもよく、多孔質炭素の細孔内にシリコンを生成または取り込むことができればよく、これらに限定されない。 Examples of porous carbon materials that make up Si-C composite particles include activated carbon, carbon fiber aggregates, carbon nanotube aggregates, carbon obtained by heat treating resins or organic materials, and hard carbon. Porous carbon materials can be produced using methods for producing activated carbon or known methods for heat treating polymers, but commercially available products may also be purchased. They are not limited to these, and any material can be used as long as it is possible to produce or incorporate silicon into the pores of the porous carbon.

　本実施形態において、Ｓｉ－Ｃ複合粒子の製造方法は特に限定されないが、例えば、次の方法を採用することができる。
　多孔質炭素材料を管状炉内に配置し、管状炉内をアルゴンガスで置換する。次いで、管状炉内に、シランガスを１～３モル％で含むシランガスおよび窒素ガスの混合ガスを２５０～３５０ｓｃｃｍの流量で流し、４５０～５５０℃、７００～８００Ｔｏｒｒ、９０～１５０分の条件で多孔質炭素材料を処理することで、生成物を得る。次いで、生成物を室温まで冷却して、Ｓｉ－Ｃ複合粒子を得る。
　Ｓｉ－Ｃ複合粒子の製造方法は、より具体的には、実施例に記載の方法を用いることができる。 In this embodiment, the method for producing the Si—C composite particles is not particularly limited, but for example, the following method can be adopted.
The porous carbon material is placed in a tubular furnace, and the atmosphere inside the furnace is replaced with argon gas. A mixed gas of silane gas containing 1 to 3 mol% silane gas and nitrogen gas is then flowed into the furnace at a flow rate of 250 to 350 sccm, and the porous carbon material is treated under conditions of 450 to 550°C, 700 to 800 Torr, and 90 to 150 minutes to obtain a product. The product is then cooled to room temperature to obtain Si—C composite particles.
More specifically, the method for producing the Si—C composite particles can be the method described in the Examples.

　本実施形態のリチウムイオン二次電池において、Ｓｉ－Ｃ複合粒子のレーザー回折散乱法による体積基準のメジアン径Ｄ５０は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは１．０μｍ以上１６．０μｍ以下、より好ましくは１．５μｍ以上１２．０μｍ以下、さらに好ましくは２．０μｍ以上１０．０μｍ以下、さらに好ましくは２．５μｍ以上８．０μｍ以下、さらに好ましくは３．０μｍ以上７．０μｍ以下である。 In the lithium ion secondary battery of this embodiment, the volume-based median diameter D50 of the Si—C composite particles measured by a laser diffraction scattering method is preferably 1.0 μm or more and 16.0 μm or less, more preferably 1.5 μm or more and 12.0 μm or less, even more preferably 2.0 μm or more and 10.0 μm or less, even more preferably 2.5 μm or more and 8.0 μm or less, and even more preferably 3.0 μm or more and 7.0 μm or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態のリチウムイオン二次電池において、負極活物質層中の負極活物質（Ｂ）の含有量は、負極活物質層の全量を１００質量部としたときに、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは１質量部以上５０質量部以下、より好ましくは５質量部以上４０質量部以下、さらに好ましくは８質量部以上３０質量部以下、さらに好ましくは１０質量部以上２８質量部以下、さらに好ましくは１２質量部以上２５質量部以下である。 In the lithium ion secondary battery of this embodiment, the content of the negative electrode active material (B) in the negative electrode active material layer, when the total amount of the negative electrode active material layer is taken as 100 parts by mass, is preferably 1 part by mass to 50 parts by mass, more preferably 5 parts by mass to 40 parts by mass, even more preferably 8 parts by mass to 30 parts by mass, even more preferably 10 parts by mass to 28 parts by mass, and even more preferably 12 parts by mass to 25 parts by mass, from the perspective of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態のリチウムイオン二次電池において、負極活物質層中の負極活物質（Ａ）の含有量をＷＡ、負極活物質層中の負極活物質（Ｂ）の含有量をＷＢとそれぞれしたときに、ＷＢに対するＷＡの比ＷＡ／ＷＢの値は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは１．０以上２０．０以下、より好ましくは２．０以上１５．０以下、さらに好ましくは２．５以上１０．０以下、さらに好ましくは２．８以上８．０以下、さらに好ましくは３．０以上６．０以下である。 In the lithium ion secondary battery of this embodiment, when the content of the negative electrode active material (A) in the negative electrode active material layer is W A and the content of the negative electrode active material (B) in the negative electrode active material layer is W B , the ratio of W A to W B , W A /W B , is preferably 1.0 or more and 20.0 or less, more preferably 2.0 or more and 15.0 or less, even more preferably 2.5 or more and 10.0 or less, even more preferably 2.8 or more and 8.0 or less, and still more preferably 3.0 or more and 6.0 or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

＜負極活物質層におけるバインダー＞
　本実施形態の負極活物質層におけるバインダーは、例えば、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリヘキサフルオロプロピレン（ＰＨＦＰ）、ポリフッ化ビニル（ＰＶＦ）、フッ化ビニリデンとヘキサフルオロプロピレンの共重合体等のフッ素樹脂；ポリ（メタ）アクリル酸等のポリカルボン酸系ポリマー；ポリアニリン類、ポリチオフェン類、ポリアセチレン類、ポリピロール類等の導電性ポリマー；スチレンブタジエンラバー（ＳＢＲ）、ブタジエンラバー（ＢＲ）、クロロプレンラバー（ＣＲ）、イソプレンラバー（ＩＲ）、アクリロニトリルブタジエンラバー（ＮＢＲ）等の合成ゴム；カルボキシメチルセルロース（ＣＭＣ）、キサンタンガム、グアーガム、ペクチン等の多糖類からなる群から選択される一種または二種以上を含む。 <Binder in Negative Electrode Active Material Layer>
The binder in the negative electrode active material layer of this embodiment includes, for example, one or more selected from the group consisting of fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), polyvinyl fluoride (PVF), and copolymers of vinylidene fluoride and hexafluoropropylene; polycarboxylic acid polymers such as poly(meth)acrylic acid; conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles; synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR); and polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin.

　これらの中でも、本実施形態の負極活物質層におけるバインダーは、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは、フッ素樹脂、ポリカルボン酸系ポリマーおよび合成ゴムからなる群より選択される一種または二種以上を含み、より好ましくは、ＰＶＤＦ、ポリカルボン酸系ポリマーおよびＳＢＲからなる群より選択される一種または二種以上を含み、さらに好ましくはポリカルボン酸系ポリマーを含み、さらに好ましくはポリ（メタ）アクリル酸を含む。 Among these, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery, the binder in the negative electrode active material layer of this embodiment preferably contains one or more types selected from the group consisting of fluororesin, polycarboxylic acid polymer, and synthetic rubber, more preferably contains one or more types selected from the group consisting of PVDF, polycarboxylic acid polymer, and SBR, even more preferably contains a polycarboxylic acid polymer, and even more preferably contains poly(meth)acrylic acid.

　本実施形態の負極活物質層中のバインダーの含有量は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、負極活物質層の全量を１００．０質量部としたとき、好ましくは０．１質量部以上１０．０質量部以下、より好ましくは１．０質量部以上７．０質量部以下、さらに好ましくは２．０質量部以上５．０質量部以下である。 In order to further improve the cycle characteristics of the lithium-ion secondary battery, the content of the binder in the negative electrode active material layer of this embodiment is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, more preferably 1.0 parts by mass or more and 7.0 parts by mass or less, and even more preferably 2.0 parts by mass or more and 5.0 parts by mass or less, when the total amount of the negative electrode active material layer is taken as 100.0 parts by mass.

＜負極活物質層における導電助剤＞
　本実施形態の負極活物質層における導電助剤は、例えば、カーボンナノファイバー等のカーボン繊維；アセチレンブラック、ケッチェンブラック等のカーボンブラック；活性炭；メソポーラスカーボン；フラーレン類；カーボンナノチューブ等の炭素材料からなる群から選択される一種または二種以上を含む。これらの中でも、本実施形態の負極活物質層における導電助剤は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは炭素材料を含み、より好ましくはカーボンナノチューブを含み、さらに好ましくは単層カーボンナノチューブを含む。 <Conductive Aid in Negative Electrode Active Material Layer>
The conductive additive in the negative electrode active material layer of this embodiment includes, for example, one or more selected from the group consisting of carbon materials such as carbon fibers such as carbon nanofibers, carbon blacks such as acetylene black and ketjen black, activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes. Among these, the conductive additive in the negative electrode active material layer of this embodiment preferably includes a carbon material, more preferably includes carbon nanotubes, and even more preferably includes single-walled carbon nanotubes, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態の負極活物質層中の導電助剤の含有量は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、負極活物質層の全量を１００．０質量部としたとき、好ましくは０．０１質量部以上５．０質量部以下、より好ましくは０．０３質量部以上１．０質量部以下、さらに好ましくは０．０５質量部以上０．５質量部以下、さらに好ましくは０．０７質量部以上０．３質量部以下である。 In order to further improve the cycle characteristics of the lithium-ion secondary battery, the content of the conductive additive in the negative electrode active material layer of this embodiment is preferably 0.01 parts by mass or more and 5.0 parts by mass or less, more preferably 0.03 parts by mass or more and 1.0 parts by mass or less, even more preferably 0.05 parts by mass or more and 0.5 parts by mass or less, and even more preferably 0.07 parts by mass or more and 0.3 parts by mass or less, when the total amount of the negative electrode active material layer is taken as 100.0 parts by mass.

＜負極集電体＞
　本実施形態の負極集電体は、例えば、銅、ステンレス鋼、ニッケル、チタン、およびこれらの合金からなる群から選択される一種または二種以上を含む。負極集電体の形状は、例えば、箔、平板またはメッシュ等の形状としてもよい。負極集電体の厚さは特に限定されないが、例えば１μｍ以上５０μｍ以下である。 <Negative electrode current collector>
The negative electrode current collector of this embodiment includes, for example, one or more selected from the group consisting of copper, stainless steel, nickel, titanium, and alloys thereof. The negative electrode current collector may be in the form of, for example, a foil, a flat plate, or a mesh. The thickness of the negative electrode current collector is not particularly limited, but is, for example, 1 μm or more and 50 μm or less.

＜負極の製造方法＞
　負極の製造方法は、一般的に公知の方法に準じておこなうことができるため特に限定されない。負極の製造方法は、例えば、実施例に記載の方法を用いることができる。 <Method of manufacturing negative electrode>
The method for producing the negative electrode is not particularly limited and can be carried out according to a generally known method, for example, the method described in the Examples.

＜正極＞
　本実施形態の正極は、正極活物質層を含む。本実施形態の正極は、リチウムイオン二次電池の電池性能をより向上できる観点から、好ましくは、正極集電体と本実施形態の正極活物質層とを備える。 <Positive electrode>
The positive electrode of this embodiment includes a positive electrode active material layer. From the viewpoint of further improving the battery performance of the lithium ion secondary battery, the positive electrode of this embodiment preferably includes a positive electrode current collector and the positive electrode active material layer of this embodiment.

＜正極活物質層＞
　本実施形態の正極活物質層は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは、本実施形態の正極活物質およびバインダーを含み、より好ましくは、本実施形態の正極活物質、バインダーおよび導電助剤を含む。 <Cathode active material layer>
From the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery, the positive electrode active material layer of the present embodiment preferably contains the positive electrode active material of the present embodiment and a binder, and more preferably contains the positive electrode active material of the present embodiment, a binder, and a conductive additive.

　本実施形態の正極活物質層の厚みは、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは１０μｍ以上２５０μｍ以下、より好ましくは１５μｍ以上２００μｍ以下、さらに好ましくは２０μｍ以上１００μｍ以下、さらに好ましくは２５μｍ以上７５μｍ以下である。 In order to further improve the cycle characteristics of the lithium-ion secondary battery, the thickness of the positive electrode active material layer in this embodiment is preferably 10 μm or more and 250 μm or less, more preferably 15 μm or more and 200 μm or less, even more preferably 20 μm or more and 100 μm or less, and even more preferably 25 μm or more and 75 μm or less.

　本実施形態の正極活物質層の密度は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは１．０ｇ／ｃｍ３以上６．０ｇ／ｃｍ３以下、より好ましくは２．０ｇ／ｃｍ３以上５．０ｇ／ｃｍ３以下、さらに好ましくは２．５ｇ／ｃｍ３以上４．５ｇ／ｃｍ３以下である。 From the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery, the density of the positive electrode active material layer of this embodiment is preferably 1.0 g/cm or more and 6.0 g/cm or less, more preferably 2.0 g/cm or more and 5.0 g/cm or less , and even more preferably 2.5 g/cm or more and 4.5 g/cm or less .

＜正極活物質＞
　本実施形態の正極活物質は、リチウムイオンを可逆的に放出または吸蔵できることで、電子輸送を容易にする観点から、電子伝導度が高い材料を用いることが好ましい。正極活物質は、電子伝導度の高さの観点から、好ましくはリチウムと遷移金属との複合酸化物、遷移金属硫化物、遷移金属酸化物およびオリビン型リチウムリン酸化物からなる群から選択される一種または二種以上を含む。リチウムと遷移金属との複合酸化物としては、例えば、リチウム－ニッケル－コバルト－マンガン複合酸化物、リチウム－ニッケル複合酸化物、リチウム－コバルト複合酸化物、リチウム－マンガン複合酸化物、リチウム－マンガン－ニッケル複合酸化物、リチウム－ニッケル－コバルト－アルミニウム複合酸化物等が挙げられる。遷移金属硫化物としては、例えば、ＴｉＳ２、ＦｅＳ、ＭｏＳ２等が挙げられる。遷移金属酸化物としては、例えば、ＭｎＯ、Ｖ２Ｏ５、Ｖ６Ｏ１３、ＴｉＯ２等が挙げられる。 <Cathode active material>
The positive electrode active material of this embodiment is preferably a material with high electronic conductivity, from the viewpoint of facilitating electron transport by being able to reversibly release or absorb lithium ions. From the viewpoint of high electronic conductivity, the positive electrode active material preferably includes one or more materials selected from the group consisting of composite oxides of lithium and transition metals, transition metal sulfides, transition metal oxides, and olivine-type lithium phosphates. Examples of composite oxides of lithium and transition metals include lithium-nickel-cobalt-manganese composite oxide, lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-manganese-nickel composite oxide, and lithium-nickel-cobalt-aluminum composite oxide. Examples of transition metal sulfides include TiS 2 , FeS, and MoS 2 . Examples of transition metal oxides include MnO, V 2 O 5 , V 6 O 13 , and TiO 2 .

　本実施形態の正極活物質層中の正極活物質の含有量は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、正極活物質層の全体を１００．０質量部としたとき、好ましくは５０．０質量部以上９９．９質量部以下、より好ましくは７５．０質量部以上９９．５質量部以下、さらに好ましくは８５．０質量部以上９９．０質量部以下、さらに好ましくは９０．０質量部以上９８．５質量部以下、さらに好ましくは９５．０質量部以上９８．０質量部以下である。 In order to further improve the cycle characteristics of the lithium-ion secondary battery, the content of the positive electrode active material in the positive electrode active material layer of this embodiment, when the entire positive electrode active material layer is taken as 100.0 parts by mass, is preferably 50.0 parts by mass or more and 99.9 parts by mass or less, more preferably 75.0 parts by mass or more and 99.5 parts by mass or less, even more preferably 85.0 parts by mass or more and 99.0 parts by mass or less, even more preferably 90.0 parts by mass or more and 98.5 parts by mass or less, and even more preferably 95.0 parts by mass or more and 98.0 parts by mass or less.

＜粒子（Ｃ）＞
　本実施形態のリチウムイオン二次電池において、正極活物質層に含まれる正極活物質は、好ましくは、リチウム－ニッケル－コバルト－マンガン複合酸化物の単結晶により構成される粒子（Ｃ１）およびリチウム－ニッケル－コバルト－マンガン複合酸化物の多結晶により構成される粒子（Ｃ２）から選択される一種または二種以上を含む粒子（Ｃ）を含む。 <Particles (C)>
In the lithium ion secondary battery of this embodiment, the positive electrode active material contained in the positive electrode active material layer preferably contains particles (C) containing one or more kinds selected from particles (C1) constituted by a single crystal of a lithium-nickel-cobalt-manganese composite oxide and particles (C2) constituted by a polycrystal of a lithium-nickel-cobalt-manganese composite oxide.

　本実施形態のリチウムイオン二次電池において、粒子（Ｃ）中のニッケルの含有量は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、粒子（Ｃ）中のニッケル、コバルト、およびマンガンの含有量の合計を１００ｍｏｌとしたときに、好ましくは８０ｍｏｌ以上、より好ましくは８０ｍｏｌ以上９９ｍｏｌ以下、さらに好ましくは８２ｍｏｌ以上９９ｍｏｌ以下、さらに好ましくは８４ｍｏｌ以上９８ｍｏｌ以下、さらに好ましくは８５ｍｏｌ以上９６ｍｏｌ以下、さらに好ましくは８６ｍｏｌ以上９５ｍｏｌ以下、さらに好ましくは８８ｍｏｌ以上９４ｍｏｌ以下である。 In the lithium ion secondary battery of this embodiment, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery, the content of nickel in particles (C) is preferably 80 mol or more, more preferably 80 mol or more and 99 mol or less, even more preferably 82 mol or more and 99 mol or less, even more preferably 84 mol or more and 98 mol or less, even more preferably 85 mol or more and 96 mol or less, even more preferably 86 mol or more and 95 mol or less, and even more preferably 88 mol or more and 94 mol or less, when the total content of nickel, cobalt, and manganese in particles (C) is taken as 100 mol.

　本実施形態のリチウムイオン二次電池において、粒子（Ｃ）中のコバルトの含有量は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、粒子（Ｃ）中のニッケル、コバルト、およびマンガンの含有量の合計を１００ｍｏｌとしたときに、好ましくは０．５ｍｏｌ以上１０ｍｏｌ以下、より好ましくは１ｍｏｌ以上１０ｍｏｌ以下、さらに好ましくは２ｍｏｌ以上１０ｍｏｌ以下、さらに好ましくは２．５ｍｏｌ以上１０ｍｏｌ以下、さらに好ましくは３ｍｏｌ以上８ｍｏｌ以下、さらに好ましくは４ｍｏｌ以上６ｍｏｌ以下である。 In the lithium ion secondary battery of this embodiment, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery, the content of cobalt in particles (C) is preferably 0.5 mol or more and 10 mol or less, more preferably 1 mol or more and 10 mol or less, even more preferably 2 mol or more and 10 mol or less, even more preferably 2.5 mol or more and 10 mol or less, even more preferably 3 mol or more and 8 mol or less, and even more preferably 4 mol or more and 6 mol or less, when the total content of nickel, cobalt, and manganese in particles (C) is taken as 100 mol.

　本実施形態のリチウムイオン二次電池において、粒子（Ｃ）中のマンガンの含有量は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、粒子（Ｃ）中のニッケル、コバルト、およびマンガンの含有量の合計を１００ｍｏｌとしたときに、好ましくは０．５ｍｏｌ以上１０ｍｏｌ以下、より好ましくは１ｍｏｌ以上１０ｍｏｌ以下、さらに好ましくは２ｍｏｌ以上１０ｍｏｌ以下、さらに好ましくは２．５ｍｏｌ以上１０ｍｏｌ以下、さらに好ましくは３ｍｏｌ以上８ｍｏｌ以下、さらに好ましくは４ｍｏｌ以上６ｍｏｌ以下である。 In the lithium ion secondary battery of this embodiment, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery, the manganese content in particles (C) is preferably 0.5 mol or more and 10 mol or less, more preferably 1 mol or more and 10 mol or less, even more preferably 2 mol or more and 10 mol or less, even more preferably 2.5 mol or more and 10 mol or less, even more preferably 3 mol or more and 8 mol or less, and even more preferably 4 mol or more and 6 mol or less, when the total content of nickel, cobalt, and manganese in particles (C) is taken as 100 mol.

　本実施形態のリチウムイオン二次電池において、粒子（Ｃ）中のニッケルのモル数をｍＮ、粒子（Ｃ）中のコバルトのモル数をｍＣ、および粒子（Ｃ）中のマンガンのモル数をｍＭとそれぞれしたときに、コバルトのモル数ｍＣとマンガンのモル数ｍＭの合計に対するニッケルのモル数ｍＮの比ｍＮ／（ｍＣ＋ｍＭ）の値は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは４以上５０以下、より好ましくは４．５以上２５以下、さらに好ましくは５以上１６以下、さらに好ましくは７以上１２以下、さらに好ましくは８以上１１以下である。 In the lithium ion secondary battery of this embodiment, when the number of moles of nickel in particles (C) is mN, the number of moles of cobalt in particles (C) is mC, and the number of moles of manganese in particles (C) is mM, the ratio mN/(mC+mM) of the number of moles of nickel mN to the sum of the number of moles of cobalt mC and the number of moles of manganese mM is preferably 4 or more and 50 or less, more preferably 4.5 or more and 25 or less, even more preferably 5 or more and 16 or less, even more preferably 7 or more and 12 or less, and even more preferably 8 or more and 11 or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

＜正極活物質層におけるバインダー＞
　本実施形態の正極活物質層におけるバインダーは、例えば、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリヘキサフルオロプロピレン（ＰＨＦＰ）、ポリフッ化ビニル（ＰＶＦ）、フッ化ビニリデンとヘキサフルオロプロピレンの共重合体等のフッ素樹脂；ポリ（メタ）アクリル酸等のポリカルボン酸系ポリマー；ポリアニリン類、ポリチオフェン類、ポリアセチレン類、ポリピロール類等の導電性ポリマー；スチレンブタジエンラバー（ＳＢＲ）、ブタジエンラバー（ＢＲ）、クロロプレンラバー（ＣＲ）、イソプレンラバー（ＩＲ）、アクリロニトリルブタジエンラバー（ＮＢＲ）等の合成ゴム；カルボキシメチルセルロース（ＣＭＣ）、キサンタンガム、グアーガム、ペクチン等の多糖類からなる群から選択される一種または二種以上を含む。 <Binder in Positive Electrode Active Material Layer>
The binder in the positive electrode active material layer of this embodiment includes, for example, one or more selected from the group consisting of fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), polyvinyl fluoride (PVF), and copolymers of vinylidene fluoride and hexafluoropropylene; polycarboxylic acid polymers such as poly(meth)acrylic acid; conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles; synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR); and polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin.

　これらの中でも、本実施形態の正極活物質層におけるバインダーは、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくはフッ素樹脂、ポリカルボン酸系ポリマー、および合成ゴムからなる群より選択される一種または二種以上を含み、より好ましくはＰＶＤＦ、ポリカルボン酸系ポリマー、およびＳＢＲからなる群より選択される一種または二種以上を含み、さらに好ましくはＰＶＤＦを含む。 Among these, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery, the binder in the positive electrode active material layer of this embodiment preferably contains one or more types selected from the group consisting of fluororesin, polycarboxylic acid polymer, and synthetic rubber, more preferably contains one or more types selected from the group consisting of PVDF, polycarboxylic acid polymer, and SBR, and even more preferably contains PVDF.

　本実施形態の正極活物質層中のバインダーの含有量は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、正極活物質層の全量を１００．０質量部としたとき、好ましくは０．０５質量部以上１０．０質量部以下、より好ましくは０．１質量部以上５．０質量部以下、さらに好ましくは０．２質量部以上２．５質量部以下、さらに好ましくは０．５質量部以上２．０質量部以下である。 In order to further improve the cycle characteristics of the lithium-ion secondary battery, the content of the binder in the positive electrode active material layer of this embodiment is preferably 0.05 parts by mass or more and 10.0 parts by mass or less, more preferably 0.1 parts by mass or more and 5.0 parts by mass or less, even more preferably 0.2 parts by mass or more and 2.5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 2.0 parts by mass or less, when the total amount of the positive electrode active material layer is taken as 100.0 parts by mass.

＜正極活物質層における導電助剤＞
　本実施形態の正極活物質層における導電助剤は、例えば、カーボンナノファイバー等のカーボン繊維；アセチレンブラック、ケッチェンブラック等のカーボンブラック；活性炭；メソポーラスカーボン；フラーレン類；カーボンナノチューブ等の炭素材料からなる群から選択される一種または二種以上を含む。これらの中でも、本実施形態の正極活物質層における導電助剤は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは炭素材料を含み、より好ましくはカーボンナノチューブを含み、さらに好ましくは単層カーボンナノチューブを含む。 <Conductive additive in positive electrode active material layer>
The conductive additive in the positive electrode active material layer of this embodiment includes, for example, one or more selected from the group consisting of carbon materials such as carbon fibers such as carbon nanofibers, carbon blacks such as acetylene black and ketjen black, activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes. Among these, the conductive additive in the positive electrode active material layer of this embodiment preferably includes a carbon material, more preferably includes carbon nanotubes, and even more preferably includes single-walled carbon nanotubes, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

　本実施形態の正極活物質層中の導電助剤の含有量は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、正極活物質層の全量を１００．０質量部としたとき、好ましくは０．０５質量部以上１０．０質量部以下、より好ましくは０．１質量部以上５．０質量部以下、さらに好ましくは０．２質量部以上２．５質量部以下、さらに好ましくは０．５質量部以上２．０質量部以下である。 In order to further improve the cycle characteristics of the lithium-ion secondary battery, the content of the conductive additive in the positive electrode active material layer of this embodiment is preferably 0.05 parts by mass or more and 10.0 parts by mass or less, more preferably 0.1 parts by mass or more and 5.0 parts by mass or less, even more preferably 0.2 parts by mass or more and 2.5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 2.0 parts by mass or less, when the total amount of the positive electrode active material layer is taken as 100.0 parts by mass.

＜正極集電体＞
　本実施形態の正極集電体は、例えば、アルミニウム、ステンレス鋼、ニッケル、チタン、およびこれらの合金からなる群から選択される一種または二種以上を含む。正極集電体の形状は、例えば、箔、平板またはメッシュ等の形状としてもよい。正極集電体の厚さは特に限定されないが、例えば、１μｍ以上５０μｍ以下である。 <Positive electrode current collector>
The positive electrode current collector of this embodiment includes, for example, one or more selected from the group consisting of aluminum, stainless steel, nickel, titanium, and alloys thereof. The positive electrode current collector may be in the form of, for example, a foil, a flat plate, or a mesh. The thickness of the positive electrode current collector is not particularly limited, but is, for example, 1 μm or more and 50 μm or less.

＜正極の製造方法＞
　正極の製造方法は、一般的に公知の方法に準じておこなうことができるため特に限定されない。正極の製造方法は、例えば、実施例に記載の方法を用いることができる。 <Method of manufacturing positive electrode>
The method for producing the positive electrode is not particularly limited and can be carried out according to a generally known method, for example, the method described in the Examples.

＜リチウムイオン二次電池のその他の構成＞
　本実施形態のリチウムイオン二次電池は、電解液、正極、および負極を含み、好ましくはセパレータをさらに含む。セパレータは、リチウムイオン二次電池に使用することができるものであれば特に限定されず、一般的に公知の物を用いることができる。 <Other configurations of lithium-ion secondary battery>
The lithium ion secondary battery of this embodiment includes an electrolyte, a positive electrode, and a negative electrode, and preferably further includes a separator. The separator is not particularly limited as long as it can be used in lithium ion secondary batteries, and generally known separators can be used.

＜セパレータ＞
　セパレータは、耐熱性を向上できる観点とセパレータの熱収縮を小さくできる観点から、好ましくは、基材と、基材の少なくとも一方の面に備えられたセラミック層とを含む。基材としては、例えば、ポリエチレン、ポリプロピレンまたはこれらを積層したポリオレフィン系の多孔質フィルム等を用いることができる。
　セラミック層は、例えば、基材上にセラミック層形成材料を塗布して乾燥させることにより形成できる。セラミック層形成材料としては、例えば、無機フィラーおよびバインダー等を任意の溶媒に分散または溶解させたものを用いることができる。無機フィラーおよびバインダーは、リチウムイオン二次電池のセパレータに使用される公知の材料であれば特に限定されない。 <Separator>
The separator preferably includes a substrate and a ceramic layer provided on at least one surface of the substrate, from the viewpoints of improving heat resistance and reducing thermal shrinkage of the separator. The substrate may be, for example, a porous polyolefin film made of polyethylene, polypropylene, or a laminate of these.
The ceramic layer can be formed, for example, by applying a ceramic layer-forming material to a substrate and drying it. The ceramic layer-forming material can be, for example, a material obtained by dispersing or dissolving an inorganic filler and a binder in a solvent. The inorganic filler and binder are not particularly limited as long as they are known materials used in separators for lithium-ion secondary batteries.

＜リチウムイオン二次電池の特性＞
　以下では、本実施形態のリチウムイオン二次電池の特性について説明する。 <Characteristics of lithium-ion secondary batteries>
The characteristics of the lithium ion secondary battery of this embodiment will be described below.

［リチウムイオン二次電池中のＬｉＦＳＩ濃度］
　本実施形態のリチウムイオン二次電池において、前記＜方法１＞による、電解液中のＬｉＦＳＩの濃度は、リチウムイオン二次電池のサイクル特性を向上できる観点から、０．６質量％以上、好ましくは０．７質量％以上、より好ましくは０．８質量％以上、さらに好ましくは０．９質量％以上、さらに好ましくは１．０質量％以上、さらに好ましくは１．１質量％以上、さらに好ましくは１．２質量％以上、さらに好ましくは１．３質量％以上、さらに好ましくは１．４質量％以上である。
　また、本実施形態のリチウムイオン二次電池において、前記＜方法１＞による、電解液中のＬｉＦＳＩの濃度は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは５．０質量％以下、より好ましくは４．０質量％以下、さらに好ましくは３．０質量％以下、さらに好ましくは２．７質量％以下である。
　また、本実施形態のリチウムイオン二次電池において、前記＜方法１＞による、電解液中のＬｉＦＳＩの濃度は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは０．６質量％以上５．０質量％以下、より好ましくは０．７質量％以上４．０質量％以下、さらに好ましくは０．８質量％以上３．０質量％以下、さらに好ましくは０．９質量％以上３．０質量％以下、さらに好ましくは１．０質量％以上３．０質量％以下、さらに好ましくは１．１質量％以上３．０質量％以下、さらに好ましくは１．２質量％以上３．０質量％以下、さらに好ましくは１．３質量％以上３．０質量％以下、さらに好ましくは１．４質量％以上２．７質量％以下である。
　前記＜方法１＞による、電解液中のＬｉＦＳＩの濃度は、例えば、リチウムイオン二次電池を作製する際に注入する電解液中のＬｉＦＳＩ濃度（ＬｉＦＳＩ濃度（作製時））や電解液の量、添加剤の量、負極活物質層中の負極活物質の種類や配合割合、正極活物質層中の正極活物質の種類や配合割合、および／または初期充放電の条件等を調整することにより調整できる。
　なお、電解液中のＬｉＦＳＩ濃度の測定方法は、より具体的には、実施例に記載の方法を採用することができる。 [LiFSI concentration in lithium ion secondary battery]
In the lithium ion secondary battery of this embodiment, the concentration of LiFSI in the electrolyte solution by <Method 1> is 0.6 mass % or more, preferably 0.7 mass % or more, more preferably 0.8 mass % or more, even more preferably 0.9 mass % or more, still more preferably 1.0 mass % or more, still more preferably 1.1 mass % or more, still more preferably 1.2 mass % or more, still more preferably 1.3 mass % or more, and still more preferably 1.4 mass % or more, from the viewpoint of improving the cycle characteristics of the lithium ion secondary battery.
In the lithium ion secondary battery of this embodiment, the concentration of LiFSI in the electrolyte solution according to <Method 1> is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, and still more preferably 2.7% by mass or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
Furthermore, in the lithium ion secondary battery of this embodiment, the concentration of LiFSI in the electrolyte by <Method 1> is preferably 0.6 mass % or more and 5.0 mass % or less, more preferably 0.7 mass % or more and 4.0 mass % or less, even more preferably 0.8 mass % or more and 3.0 mass % or less, even more preferably 0.9 mass % or more and 3.0 mass % or less, even more preferably 1.0 mass % or more and 3.0 mass % or less, even more preferably 1.1 mass % or more and 3.0 mass % or less, even more preferably 1.2 mass % or more and 3.0 mass % or less, even more preferably 1.3 mass % or more and 3.0 mass % or less, and even more preferably 1.4 mass % or more and 2.7 mass % or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.
The LiFSI concentration in the electrolyte solution according to Method 1 can be adjusted by, for example, adjusting the LiFSI concentration in the electrolyte solution (LiFSI concentration (at the time of preparation)) injected when preparing the lithium-ion secondary battery, the amount of the electrolyte solution, the amount of additives, the type and blending ratio of the negative electrode active material in the negative electrode active material layer, the type and blending ratio of the positive electrode active material in the positive electrode active material layer, and/or the conditions of initial charge and discharge.
More specifically, the method for measuring the LiFSI concentration in the electrolyte solution can be the method described in the Examples.

［２５℃での容量維持率Ｒ２５］
　本実施形態のリチウムイオン二次電池において、下記＜方法２＞による、２５℃での容量維持率Ｒ２５は、リチウムイオン二次電池のサイクル特性をより向上できる観点から、好ましくは８７．０％以上、より好ましくは８７．５％以上、さらに好ましくは８８．０％以上、さらに好ましくは８８．５％以上、さらに好ましくは８９．０％以上、さらに好ましくは８９．５％以上、さらに好ましくは９０．０％以上、さらに好ましくは９０．５％以上、さらに好ましくは９１．０％以上、さらに好ましくは９１．５％以上、さらに好ましくは９２．０％以上である。
　２５℃での容量維持率Ｒ２５の上限は、特に制限されないが、例えば１００％未満であり、９９．０％以下であってもよく、９８．０％以下であってもよく、９５．０％以下であってもよい。 [Capacity retention rate R 25 at 25°C]
In the lithium ion secondary battery of this embodiment, the capacity retention rate R25 at 25°C according to the following <Method 2> is, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery, preferably 87.0% or more, more preferably 87.5% or more, even more preferably 88.0% or more, even more preferably 88.5% or more, even more preferably 89.0% or more, even more preferably 89.5% or more, even more preferably 90.0% or more, even more preferably 90.5% or more, even more preferably 91.0% or more, even more preferably 91.5% or more, and even more preferably 92.0% or more.
The upper limit of the capacity retention rate R 25 at 25° C. is not particularly limited, but is, for example, less than 100%, and may be 99.0% or less, 98.0% or less, or 95.0% or less.

＜方法２＞
　本実施形態のリチウムイオン二次電池を２５℃の恒温槽内に配置する。次いで、下記＜充放電サイクル＞によってリチウムイオン二次電池の充放電を行い、１回目の放電容量を測定する。次いで、下記＜充放電サイクル＞によってリチウムイオン二次電池の充放電を合計４９９回になるまで繰り返す。次いで、下記＜充放電サイクル＞によってリチウムイオン二次電池の充放電を行い、５００回目の放電容量を測定する。次いで、下記式（２）から容量維持率Ｒ２５を算出する。
式（２）：容量維持率Ｒ２５＝（５００回目の放電容量）／（１回目の放電容量）×１００ <Method 2>
The lithium ion secondary battery of this embodiment is placed in a thermostatic chamber at 25°C. Next, the lithium ion secondary battery is charged and discharged according to the following <charge and discharge cycle>, and the first discharge capacity is measured. Next, the lithium ion secondary battery is repeatedly charged and discharged according to the following <charge and discharge cycle> until a total of 499 cycles have been completed. Next, the lithium ion secondary battery is charged and discharged according to the following <charge and discharge cycle>, and the 500th discharge capacity is measured. Next, the capacity retention rate R25 is calculated according to the following formula (2).
Equation (2): Capacity retention rate R 25 =(500th discharge capacity)/(1st discharge capacity)×100

＜充放電サイクル＞
　上限電圧４．２５Ｖに達するまで３０ｍＡでリチウムイオン二次電池を充電する。次いで、上限電圧４．２５Ｖに達した後は、充電を開始してからの経過時間が２．５時間になるまでリチウムイオン二次電池を定電圧で充電する。次いで、下限電圧２．５Ｖに達するまで３０ｍＡの定電流でリチウムイオン二次電池を放電する。 <Charge/discharge cycle>
The lithium ion secondary battery is charged at 30 mA until it reaches an upper limit voltage of 4.25 V. After the upper limit voltage of 4.25 V is reached, the lithium ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging. The lithium ion secondary battery is then discharged at a constant current of 30 mA until it reaches a lower limit voltage of 2.5 V.

＜リチウムイオン二次電池の用途＞
　本実施形態のリチウムイオン二次電池は、リチウムイオン二次電池のサイクル特性を向上できるため、様々な用途に使用できる。本実施形態のリチウムイオン二次電池は、例えば、産業用、民生用、自動車用、住宅用等に使用できるが、これらに限定されない。 <Applications of lithium-ion secondary batteries>
The lithium ion secondary battery of the present embodiment can improve the cycle characteristics of the lithium ion secondary battery, and therefore can be used in a variety of applications, including, but not limited to, industrial, consumer, automotive, and residential applications.

＜リチウムイオン二次電池モジュール＞
　本実施形態のリチウムイオン二次電池モジュールは、本実施形態のリチウムイオン二次電池を備える。本実施形態のリチウムイオン二次電池モジュールは、好ましくは、直列または並列に接続された、二以上の本実施形態のリチウムイオン二次電池を備える。本実施形態のリチウムイオン二次電池モジュールは、より好ましくは、直列または並列に接続された、二以上の本実施形態のリチウムイオン二次電池を収容できる筐体をさらに備える。本実施形態のリチウムイオン二次電池モジュールは、さらに好ましくは、過電流からリチウムイオン二次電池を保護する保護回路、リチウムイオン二次電池の電極間の電圧を平準化するバランス回路、リチウムイオン二次電池を制御する制御器、リチウムイオン二次電池を冷却できる冷却器、リチウムイオン二次電池を加熱できる加熱器からなる群から選択される一種または二種以上をさらに備える。 <Lithium-ion secondary battery module>
The lithium-ion secondary battery module of this embodiment includes the lithium-ion secondary battery of this embodiment. The lithium-ion secondary battery module of this embodiment preferably includes two or more lithium-ion secondary batteries of this embodiment connected in series or parallel. The lithium-ion secondary battery module of this embodiment more preferably further includes a housing capable of accommodating two or more lithium-ion secondary batteries of this embodiment connected in series or parallel. The lithium-ion secondary battery module of this embodiment more preferably further includes one or more devices selected from the group consisting of a protection circuit that protects the lithium-ion secondary battery from overcurrent, a balancing circuit that equalizes the voltage between the electrodes of the lithium-ion secondary battery, a controller that controls the lithium-ion secondary battery, a cooler that can cool the lithium-ion secondary battery, and a heater that can heat the lithium-ion secondary battery.

　本実施形態のリチウムイオン二次電池モジュールは、電気的に接続した二以上のリチウムイオン二次電池モジュールと電池制御システムとを備える電池システムに用いることができる。電池システムとしては、例えば、電池パック、定置用蓄電池システム、自動車の動力用蓄電池システム、自動車の補機用蓄電池システム、非常電源用蓄電池システム等が挙げられる。 The lithium-ion secondary battery module of this embodiment can be used in a battery system comprising two or more electrically connected lithium-ion secondary battery modules and a battery control system. Examples of battery systems include battery packs, stationary storage battery systems, automotive power storage battery systems, automotive auxiliary storage battery systems, and emergency power storage battery systems.

　以上、本発明の実施形態について述べたが、これらは本発明の例示であり、上記以外の様々な構成を採用することもできる。
　また、本発明は前述の実施形態に限定されるものではなく、本発明の効果を損なわない範囲での変形、改良等は本発明に含まれるものである。 Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations can also be adopted.
Furthermore, the present invention is not limited to the above-described embodiment, and modifications and improvements within the scope that do not impair the effects of the present invention are included in the present invention.

　以下、本実施形態を、実施例等を参照して詳細に説明する。なお、本実施形態は、これらの実施例の記載に何ら限定されるものではない。 The present embodiment will be described in detail below with reference to examples. Note that the present embodiment is in no way limited to the descriptions of these examples.

　はじめに、各例において用いた材料を示す。 First, the materials used in each example are listed.

　負極活物質には、以下の材料（以下、負極活物質１とも呼ぶ。）を用いた。負極活物質１には、以下の負極活物質（Ａ）と負極活物質（Ｂ）とを組み合わせて用いた。なお、負極活物質（Ａ）と負極活物質（Ｂ）は、負極活物質（Ａ）：負極活物質（Ｂ）＝８０：２０（質量比）となるように配合した。 The following material (hereinafter also referred to as negative electrode active material 1) was used as the negative electrode active material. Negative electrode active material 1 was made by combining the following negative electrode active material (A) and negative electrode active material (B). The negative electrode active material (A) and negative electrode active material (B) were blended in a ratio of negative electrode active material (A):negative electrode active material (B) = 80:20 (mass ratio).

［負極活物質（Ａ）］
　負極活物質（Ａ）には、以下の黒鉛粉末（Ａ１）と黒鉛粉末（Ａ２）とを組み合わせて用いた。なお、負極活物質（Ａ１）と負極活物質（Ａ２）は、負極活物質（Ａ１）：負極活物質（Ａ２）＝５０：５０（質量比）となるように配合した。 [Negative electrode active material (A)]
The negative electrode active material (A) was a combination of the following graphite powder (A1) and graphite powder (A2). The negative electrode active material (A1) and the negative electrode active material (A2) were blended in a mass ratio of negative electrode active material (A1):negative electrode active material (A2) = 50:50.

＜黒鉛粉末（Ａ１）＞
　黒鉛粉末（Ａ１）として、表面に非晶質炭素を含む人造黒鉛粒子を用いた。黒鉛粉末（Ａ１）には、以下の黒鉛粉末１を用いた。
・黒鉛粉末１（表面に非晶質炭素を含む人造黒鉛粒子、メジアン径Ｄ５０：１４．０μｍ） <Graphite powder (A1)>
As the graphite powder (A1), artificial graphite particles containing amorphous carbon on the surface were used. As the graphite powder (A1), the following graphite powder 1 was used.
Graphite powder 1 (artificial graphite particles containing amorphous carbon on the surface, median diameter D 50 : 14.0 μm)

＜黒鉛粉末（Ａ２）＞
　黒鉛粉末（Ａ２）として、表面に非晶質炭素を含まない人造黒鉛粒子を用いた。黒鉛粉末（Ａ２）には、以下の黒鉛粉末２を用いた。
・黒鉛粉末２（表面に非晶質炭素を含まない人造黒鉛粒子、メジアン径Ｄ５０：９．０μｍ） <Graphite powder (A2)>
As the graphite powder (A2), artificial graphite particles not containing amorphous carbon on the surface were used. As the graphite powder (A2), the following graphite powder 2 was used.
Graphite powder 2 (artificial graphite particles not containing amorphous carbon on the surface, median diameter D 50 : 9.0 μm)

［負極活物質（Ｂ）］
　負極活物質（Ｂ）には、以下のＳｉ－Ｃ複合粒子（以下、Ｓｉ／Ｃ粒子とも呼ぶ。）を用いた。
　Ｓｉ－Ｃ複合粒子には、以下のＳｉ／Ｃ粒子１を用いた。
・Ｓｉ／Ｃ粒子１（メジアン径Ｄ５０：４．８μｍ、下記の＜Ｓｉ／Ｃ粒子１の作製＞に従って作製した粒子） [Negative electrode active material (B)]
The negative electrode active material (B) used was the following Si—C composite particles (hereinafter also referred to as Si/C particles).
The Si--C composite particles used were the following Si/C particles 1.
Si/C particles 1 (median diameter D 50 : 4.8 μm, particles prepared according to the <Preparation of Si/C particles 1> below)

＜Ｓｉ／Ｃ粒子１の作製＞
　多孔質炭素材料１（メジアン径Ｄ５０：４．８μｍ）を管状炉内に配置し、管状炉内をアルゴンガスで置換した。その後、管状炉内に、シランガス２モル％、窒素ガス９８モル％の混合ガスを３００ｓｃｃｍの流量で流し、５００℃、７６０Ｔｏｒｒ、１２０分の条件で、多孔質炭素材料１を処理することで、生成物を得た。次いで、生成物を室温まで冷却して、Ｓｉ／Ｃ粒子１を得た。
　得られたＳｉ／Ｃ粒子１の断面について、エネルギー分散型Ｘ線分析装置を用いてＥＤＳマッピングを行った。ＥＤＳマッピングの結果から、Ｓｉ／Ｃ粒子１がシリコンを含むことと、Ｓｉ／Ｃ粒子１においてシリコンが多孔質炭素材料１の細孔内の少なくとも一部に存在することと、をそれぞれ確認した。 <Preparation of Si/C Particles 1>
A porous carbon material 1 (median diameter D50 : 4.8 μm) was placed in a tubular furnace, and the inside of the tubular furnace was replaced with argon gas. A mixed gas of 2 mol% silane gas and 98 mol% nitrogen gas was then flowed into the tubular furnace at a flow rate of 300 sccm, and the porous carbon material 1 was treated under conditions of 500°C, 760 Torr, and 120 minutes to obtain a product. The product was then cooled to room temperature to obtain Si/C particles 1.
An energy dispersive X-ray analyzer was used to perform EDS mapping of the cross section of the obtained Si/C particle 1. The results of the EDS mapping confirmed that the Si/C particle 1 contains silicon and that silicon is present in at least a portion of the pores of the porous carbon material 1 in the Si/C particle 1.

　正極活物質には、以下の正極活物質１を用いた。
・正極活物質１：リチウム－ニッケル－コバルト－マンガン複合酸化物の単結晶により構成され、ニッケル、コバルトおよびマンガンのｍｏｌ比がニッケル：コバルト：マンガン＝９０：５：５である粒子（メジアン径Ｄ５０：３．５μｍ） The positive electrode active material used was the following positive electrode active material 1.
Positive electrode active material 1: Particles composed of a single crystal of lithium-nickel-cobalt-manganese composite oxide, in which the molar ratio of nickel, cobalt, and manganese is nickel:cobalt:manganese=90:5:5 (median diameter D 50 : 3.5 μm)

　電解液には、以下の材料を用いた。
・溶媒１：エチレンカーボネート（以下、ＥＣとも呼ぶ。）
・溶媒２：エチルメチルカーボネート（以下、ＥＭＣとも呼ぶ。）
・電解質：六フッ化リン酸リチウム（ＬｉＰＦ６）
・電解質：リチウムビス（フルオロスルホニル）イミド（ＬｉＦＳＩ）
　セパレータには、以下の材料を用いた。
・セパレータ：微多孔性ポリエチレンフィルムの両面にセラミックコートした厚さ１０μｍのもの The following materials were used for the electrolyte.
Solvent 1: Ethylene carbonate (hereinafter also referred to as EC)
Solvent 2: Ethyl methyl carbonate (hereinafter also referred to as EMC)
Electrolyte: Lithium hexafluorophosphate (LiPF 6 )
Electrolyte: Lithium bis(fluorosulfonyl)imide (LiFSI)
The following materials were used for the separator.
Separator: 10 μm thick microporous polyethylene film with ceramic coating on both sides

　負極には、負極活物質以外に、以下の材料を用いた。
・負極集電体：銅箔（厚さ：８μｍ）
・バインダー：ポリアクリル酸（以下、ＰＡＡとも呼ぶ。）
・導電助剤：単層カーボンナノチューブ（以下、ＣＮＴとも呼ぶ。）
・溶媒：純水 In addition to the negative electrode active material, the following materials were used for the negative electrode.
Negative electrode current collector: copper foil (thickness: 8 μm)
Binder: Polyacrylic acid (hereinafter referred to as PAA)
Conductive additive: single-walled carbon nanotubes (hereinafter also referred to as CNTs)
・Solvent: Pure water

　正極には、正極活物質以外に、以下の材料を用いた。
・正極集電体：アルミニウム箔（厚さ：１２μｍ）
・バインダー：ポリフッ化ビニリデン（以下、ＰＶＤＦとも呼ぶ。）
・導電助剤：単層カーボンナノチューブ（以下、ＣＮＴとも呼ぶ。）
・溶媒：Ｎ－メチル－２－ピロリドン（以下、ＮＭＰとも呼ぶ。） In addition to the positive electrode active material, the following materials were used for the positive electrode.
Positive electrode current collector: aluminum foil (thickness: 12 μm)
Binder: Polyvinylidene fluoride (hereinafter also referred to as PVDF)
Conductive additive: single-walled carbon nanotubes (hereinafter also referred to as CNTs)
Solvent: N-methyl-2-pyrrolidone (hereinafter also referred to as NMP)

＜正極活物質および負極活物質の粒子径の測定方法＞
　レーザ回折式粒子径分布測定装置（島津製作所製、型番：ＳＡＬＤ－２３００）を用いて、正極活物質および負極活物質それぞれの、レーザー回折散乱法による体積基準のメジアン径Ｄ５０を測定した。ここで、正極活物質のメジアン径Ｄ５０は、正極活物質を分散媒（０．１質量％ヘキサメタリン酸ナトリウム水溶液）に懸濁させ、超音波分散した後に測定した。また、負極活物質のメジアン径Ｄ５０は、負極活物質を分散媒（０．１質量％ヘキサメタリン酸ナトリウム水溶液）に懸濁させ、超音波分散した後に測定した。測定は５回おこない、平均値をメジアン径Ｄ５０とした。 <Method for measuring particle diameters of positive electrode active material and negative electrode active material>
Using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, model number: SALD-2300), the volume-based median diameter D 50 of each of the positive electrode active material and the negative electrode active material was measured by laser diffraction scattering. Here, the median diameter D 50 of the positive electrode active material was measured after suspending the positive electrode active material in a dispersion medium (0.1% by mass sodium hexametaphosphate aqueous solution) and ultrasonically dispersing it. Furthermore, the median diameter D 50 of the negative electrode active material was measured after suspending the negative electrode active material in a dispersion medium (0.1% by mass sodium hexametaphosphate aqueous solution) and ultrasonically dispersing it. The measurement was performed five times, and the average value was taken as the median diameter D 50 .

　（実施例１～３、比較例１）
＜リチウムイオン二次電池の作製＞
　以下の工程でリチウムイオン二次電池を作製した。以下では、いくつかの工程に分けて具体的に説明する。 (Examples 1 to 3, Comparative Example 1)
<Fabrication of Lithium-ion Secondary Battery>
A lithium ion secondary battery was fabricated through the following steps, which will be described in detail below.

　まず、以下の手順で、各例のリチウムイオン二次電池に用いる電解液をそれぞれ作製した。
　エチレンカーボネートとエチルメチルカーボネートを、ＥＣ：ＥＭＣ＝３０：７０（質量比）で混合して混合溶媒を得た。得られた混合溶媒に、六フッ化リン酸リチウム（ＬｉＰＦ６）を、その含有量が１２質量％となるように溶解させた。また、リチウムビス（フルオロスルホニル）イミド（ＬｉＦＳＩ）の含有量が、表１に記載されたＬｉＦＳＩ濃度（作製時）となるように、混合溶媒にＬｉＦＳＩを溶解させて、各例の電解液をそれぞれ作製した。 First, the electrolyte solutions to be used in the lithium ion secondary batteries of each example were prepared according to the following procedure.
Ethylene carbonate and ethyl methyl carbonate were mixed in a mass ratio of 30:70 (EC:EMC) to obtain a mixed solvent. Lithium hexafluorophosphate (LiPF 6 ) was dissolved in the obtained mixed solvent to a content of 12 mass%. Furthermore, lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in the mixed solvent to obtain the LiFSI concentration (at the time of preparation) shown in Table 1, thereby preparing the electrolyte solutions of each example.

　次に、以下の手順で、各例のリチウムイオン二次電池に用いる正極をそれぞれ作製した。
　表１に示す正極活物質、バインダー（ＰＶＤＦ）、および導電助剤（ＣＮＴ）を、正極活物質：ＰＶＤＦ：ＣＮＴ＝９７．５：１．５：１．０（質量比）で溶媒（ＮＭＰ）に分散させて、正極スラリーをそれぞれ作製した。
　次いで、正極スラリーを、正極集電体である厚さ１２μｍのアルミニウム箔に、単位面積当たりの初回充電容量が４．０ｍＡｈ／ｃｍ２となるような塗布量で塗布した。その後、塗布した正極スラリーを乾燥させて、正極積層体を得た。次いで、ロールプレス機を用いて、正極活物質層の密度が３．５ｇ／ｃｍ３となるような圧力で正極積層体をプレスして、各例の正極をそれぞれ作製した。 Next, the positive electrodes to be used in the lithium ion secondary batteries of each example were fabricated in the following manner.
The positive electrode active material, binder (PVDF), and conductive additive (CNT) shown in Table 1 were dispersed in a solvent (NMP) at a mass ratio of positive electrode active material:PVDF:CNT=97.5:1.5:1.0 to prepare positive electrode slurries.
Next, the positive electrode slurry was applied to a 12 μm thick aluminum foil positive electrode current collector in an amount such that the initial charge capacity per unit area was 4.0 mAh/cm 2. The applied positive electrode slurry was then dried to obtain a positive electrode laminate. Next, using a roll press, the positive electrode laminate was pressed with a pressure such that the density of the positive electrode active material layer was 3.5 g/cm 3 , to produce each positive electrode of each example.

　次に、以下の手順で、各例のリチウムイオン二次電池に用いる負極をそれぞれ作製した。
　表１に示す負極活物質、バインダー（ＰＡＡ）、および導電助剤（ＣＮＴ）を、負極活物質：ＰＡＡ：ＣＮＴ＝９６．９：３．０：０．１（質量比）で溶媒（純水）に分散させて、負極スラリーをそれぞれ作製した。
　次いで、負極スラリーを、負極集電体である厚さ８μｍの銅箔に、単位面積当たりの初回充電容量が４．３ｍＡｈ／ｃｍ２となるような塗布量で塗布した。その後、塗布した負極スラリーを乾燥させて、負極積層体を得た。次いで、ロールプレス機を用いて、負極活物質層の密度が１．６５ｇ／ｃｍ３となるような圧力で負極積層体をプレスして、各例の負極をそれぞれ作製した。 Next, the negative electrodes to be used in the lithium ion secondary batteries of each example were fabricated in the following manner.
The negative electrode active material, binder (PAA), and conductive additive (CNT) shown in Table 1 were dispersed in a solvent (pure water) at a mass ratio of negative electrode active material:PAA:CNT = 96.9:3.0:0.1 to prepare negative electrode slurries.
Next, the negative electrode slurry was applied to an 8 μm thick copper foil negative electrode current collector in an amount such that the initial charge capacity per unit area was 4.3 mAh/cm 2. The applied negative electrode slurry was then dried to obtain a negative electrode laminate. Next, using a roll press, the negative electrode laminate was pressed at a pressure such that the density of the negative electrode active material layer was 1.65 g/cm 3 , to produce each negative electrode of each example.

　次に、以下の手順で、各例のリチウムイオン二次電池をそれぞれ作製した。
　両面塗工した正極１枚と片面塗工した負極２枚を、セパレータを介して互いの塗工面が向かい合うように対向させ、負極、セパレータ、正極、セパレータ、負極の順番で積層した。このようにして作製した積層体を、アルミニウムを主成分とするフィルムを加工して成型されたラミネート外装体で包み込んだ。このとき、集電用に切り出したアルミニウム箔および銅箔がラミネート製のフィルムから突出するようにした。その後、集電用の箔を突出させた部分を含む辺とそれ以外の２辺を熱溶着して、一辺のみが開いた状態のラミネート型のセルを作製した。
　上記ラミネート型のセルの開口部から、上記で調製した所定量の電解液を注液した。そして、ラミネート型のセルを減圧封止することで、ラミネート型のリチウムイオン二次電池を作製した。
　ここで、注液する電解液の量は、正極活物質と負極活物質の合計を１００質量部としたときに、電解液が３０質量部となるようにした。 Next, the lithium ion secondary batteries of each example were fabricated in the following manner.
One double-sided coated positive electrode and two single-sided coated negative electrodes were arranged with the coated surfaces facing each other through a separator, and stacked in the following order: negative electrode, separator, positive electrode, separator, negative electrode. The stack thus produced was then wrapped in a laminated outer casing formed by processing a film primarily composed of aluminum. The aluminum foil and copper foil cut out for current collection protruded from the laminated film. The edge containing the protruding current collection foil and the other two edges were then heat-sealed to produce a laminated cell with only one edge open.
A predetermined amount of the electrolyte solution prepared above was poured into the opening of the laminated cell, and the laminated cell was then sealed under reduced pressure to produce a laminated lithium ion secondary battery.
The amount of the electrolyte solution to be injected was set so that the amount of the electrolyte solution was 30 parts by mass when the total amount of the positive electrode active material and the negative electrode active material was 100 parts by mass.

＜リチウムイオン二次電池の初期充放電＞
　各例のリチウムイオン二次電池について、下記条件で初期充放電を行って、負極活物質の表面にＳＥＩ膜を形成することで、各例の初期充放電後のリチウムイオン二次電池をそれぞれ得た。なお、以下では、リチウムイオン二次電池の充放電は、温度２５℃の環境下で、充放電装置を用いて行った。
　各例のリチウムイオン二次電池を、充電電流０．０５Ｃで電池電圧３．２Ｖまで充電し、次いで、１２時間放置することでＰｒｅ充電を行った。
　次に、充電電流０．０５Ｃで電池電圧４．２５Ｖまで定電流充電を行った。電池電圧４．２５Ｖ到達後は、電流値が０．０１５Ｃに低下するまで定電圧充電を行った。次いで、１０分間放置した。その後、放電電流０．３３Ｃで電池電圧２．５Ｖまで定電流放電を行った。電池電圧２．５Ｖ到達後は、１０分間放置した。
　次に、充電電流０．３３Ｃで電池電圧４．２５Ｖまで定電流充電を行った。電池電圧４．２５Ｖ到達後は、電流値が０．０５Ｃに低下するまで定電圧充電を行った。次いで、充電したリチウムイオン二次電池を温度４５℃環境下にて、電池電圧をモニターしながら４８時間保存した。保存後、リチウムイオン二次電池を温度２５℃環境下に戻して、放電電流１Ｃで電池電圧２．５Ｖまで定電流放電を行った。次いで、放電電流０．３３Ｃで電池電圧２．５Ｖまで定電流放電を行った。電池電圧２．５Ｖ到達後は、１０分間放置した。
　次に、充電電流０．３３Ｃで電池電圧４．２５Ｖまで定電流充電を行った。電池電圧４．２５Ｖ到達後は、電流値が０．０５Ｃに低下するまで定電圧充電を行った。次いで、充電終了から１０分間経過後、放電電流１Ｃで電池電圧２．５Ｖまで定電流放電を行った。次いで、放電電流０．３３Ｃで電池電圧２．５Ｖまで定電流放電を行った。電池電圧２．５Ｖ到達後は、１０分間放置した。
　次に、充電電流０．３３Ｃで電池電圧４．２５Ｖまで定電流充電を行った。電池電圧４．２５Ｖ到達後は、電流値が０．０５Ｃに低下するまで定電圧充電を行った。次いで、１０分間放置した。その後、放電電流０．３３Ｃで電池電圧２．５Ｖまで定電流放電を行った。 <Initial charging and discharging of lithium-ion secondary batteries>
The lithium ion secondary battery of each example was initially charged and discharged under the following conditions to form an SEI film on the surface of the negative electrode active material, thereby obtaining the lithium ion secondary battery of each example after initial charge and discharge. Note that, hereinafter, the charge and discharge of the lithium ion secondary battery was performed using a charge and discharge device in an environment at a temperature of 25°C.
The lithium ion secondary battery of each example was charged at a charging current of 0.05 C up to a battery voltage of 3.2 V, and then left to stand for 12 hours to perform pre-charging.
Next, constant current charging was performed at a charging current of 0.05 C until the battery voltage reached 4.25 V. After the battery voltage reached 4.25 V, constant voltage charging was performed until the current value decreased to 0.015 C. The battery was then left for 10 minutes. Thereafter, constant current discharging was performed at a discharge current of 0.33 C until the battery voltage reached 2.5 V. After the battery voltage reached 2.5 V, the battery was left for 10 minutes.
Next, constant current charging was performed at a charging current of 0.33 C until the battery voltage reached 4.25 V. After the battery voltage reached 4.25 V, constant voltage charging was performed until the current value dropped to 0.05 C. The charged lithium-ion secondary battery was then stored for 48 hours in an environment at a temperature of 45°C while the battery voltage was monitored. After storage, the lithium-ion secondary battery was returned to an environment at a temperature of 25°C and constant current discharge was performed at a discharge current of 1 C until the battery voltage reached 2.5 V. Next, constant current discharge was performed at a discharge current of 0.33 C until the battery voltage reached 2.5 V. After the battery voltage reached 2.5 V, the battery was left for 10 minutes.
Next, constant current charging was performed at a charging current of 0.33 C until the battery voltage reached 4.25 V. After the battery voltage reached 4.25 V, constant voltage charging was performed until the current value decreased to 0.05 C. Next, 10 minutes after the end of charging, constant current discharging was performed at a discharge current of 1 C until the battery voltage reached 2.5 V. Next, constant current discharging was performed at a discharge current of 0.33 C until the battery voltage reached 2.5 V. After the battery voltage reached 2.5 V, the battery was left to stand for 10 minutes.
Next, constant current charging was performed at a charging current of 0.33 C until the battery voltage reached 4.25 V. After the battery voltage reached 4.25 V, constant voltage charging was performed until the current value decreased to 0.05 C. The battery was then left for 10 minutes. Thereafter, constant current discharging was performed at a discharging current of 0.33 C until the battery voltage reached 2.5 V.

＜リチウムイオン二次電池の特性の測定＞
　各例で得られた、初期充放電後のリチウムイオン二次電池の特性を以下の方法で測定した。測定結果を表１に示す。 <Measurement of lithium-ion secondary battery characteristics>
The characteristics of the lithium ion secondary batteries obtained in each example after the initial charge and discharge were measured by the following method. The measurement results are shown in Table 1.

［初期充放電後のＬｉＦＳＩ濃度］
　各例の初期充放電後のリチウムイオン二次電池について、初期充放電後のＬｉＦＳＩ濃度を以下の方法で測定した。
　各例の初期充放電後のリチウムイオン二次電池を、不活性ガス雰囲気下、温度２５℃、相対湿度３％ＲＨ以下の環境で分解した。次いで、分解したリチウムイオン二次電池から採取した０．２ｇの電解液を、１．０ｇの重アセトニトリルに溶解させて第１サンプルを作製した。次いで、基準物質として０．００２ｇの六フッ化ベンゼンを第１サンプルに添加して第２サンプルを作製した。次いで、０．５ｇの第２サンプルを用いて、１９Ｆ－ＮＭＲ法により、第２サンプル中のＬｉＦＳＩの量を測定した。次いで、第２サンプル中のＬｉＦＳＩの量から第１サンプル中のＬｉＦＳＩの量を算出した。次いで、下記式（１）から電解液中のＬｉＦＳＩの濃度（初期充放電後のＬｉＦＳＩ濃度）を算出した。
式（１）：電解液中のＬｉＦＳＩの濃度＝（第１サンプル中のＬｉＦＳＩの量）／（分解したリチウムイオン二次電池から採取した電解液の量）×１００ [LiFSI concentration after initial charge/discharge]
For the lithium ion secondary battery of each example after the initial charge and discharge, the LiFSI concentration after the initial charge and discharge was measured by the following method.
The lithium-ion secondary battery after initial charge and discharge in each example was decomposed in an inert gas atmosphere at a temperature of 25°C and a relative humidity of 3% or less. Next, 0.2 g of the electrolyte solution collected from the decomposed lithium-ion secondary battery was dissolved in 1.0 g of deuterated acetonitrile to prepare a first sample. Next, 0.002 g of hexafluorobenzene was added to the first sample as a reference material to prepare a second sample. Next, using 0.5 g of the second sample, the amount of LiFSI in the second sample was measured by 19F -NMR. Next, the amount of LiFSI in the first sample was calculated from the amount of LiFSI in the second sample. Next, the LiFSI concentration in the electrolyte (LiFSI concentration after initial charge and discharge) was calculated using the following formula (1):
Equation (1): Concentration of LiFSI in the electrolyte solution = (Amount of LiFSI in the first sample) / (Amount of electrolyte solution collected from the disassembled lithium-ion secondary battery) × 100

　上述の１９Ｆ－ＮＭＲ法による測定と分析は、以下の条件で行った。
・核磁気共鳴装置：ＪＮＭ－ＥＣＡ４００ＷＢ（日本電子株式会社製）
・測定項目：１９Ｆ
・溶媒：重アセトニトリル
・観測周波数：４００ＭＨｚ
・積算回数：１２８回
・化学シフトの標準物質：六フッ化ベンゼン
・１９Ｆ－ＮＭＲスペクトル測定方法：シングルパルス法
・測定温度：２５℃ The above-mentioned measurement and analysis by 19 F-NMR method were carried out under the following conditions.
Nuclear magnetic resonance apparatus: JNM-ECA400WB (manufactured by JEOL Ltd.)
・Measurement item: 19F
Solvent: deuterated acetonitrile Observation frequency: 400 MHz
Number of accumulations: 128 times; Chemical shift standard: hexafluorobenzene; 19F -NMR spectrum measurement method: single pulse method; Measurement temperature: 25°C

［２５℃での容量維持率Ｒ２５］
　各例の初期充放電後のリチウムイオン二次電池について、２５℃での容量維持率Ｒ２５を以下の方法で測定した。
　各例の初期充放電後のリチウムイオン二次電池を２５℃の恒温槽内に配置した。次いで、下記＜充放電サイクル＞によってリチウムイオン二次電池の充放電を行い、１回目の放電容量を測定した。次いで、下記＜充放電サイクル＞によってリチウムイオン二次電池の充放電を合計４９９回になるまで繰り返した。次いで、下記＜充放電サイクル＞によってリチウムイオン二次電池の充放電を行い、５００回目の放電容量を測定した。次いで、下記式（２）から容量維持率Ｒ２５を算出した。
式（２）：容量維持率Ｒ２５＝（５００回目の放電容量）／（１回目の放電容量）×１００ [Capacity retention rate R 25 at 25°C]
For each example of the lithium ion secondary battery after the initial charge and discharge, the capacity retention rate R 25 at 25° C. was measured by the following method.
The lithium ion secondary battery after the initial charge and discharge of each example was placed in a thermostatic chamber at 25°C. The lithium ion secondary battery was then charged and discharged according to the following <charge and discharge cycle>, and the first discharge capacity was measured. The lithium ion secondary battery was then repeatedly charged and discharged 499 times in total according to the following <charge and discharge cycle>. The lithium ion secondary battery was then charged and discharged according to the following <charge and discharge cycle>, and the 500th discharge capacity was measured. The capacity retention rate R25 was then calculated according to the following formula (2).
Equation (2): Capacity retention rate R 25 =(500th discharge capacity)/(1st discharge capacity)×100

＜充放電サイクル＞
　上限電圧４．２５Ｖに達するまで３０ｍＡでリチウムイオン二次電池を充電した。次いで、上限電圧４．２５Ｖに達した後は、充電を開始してからの経過時間が２．５時間になるまでリチウムイオン二次電池を定電圧で充電した。次いで、下限電圧２．５Ｖに達するまで３０ｍＡの定電流で、リチウムイオン二次電池を放電した。 <Charge/discharge cycle>
The lithium ion secondary battery was charged at 30 mA until the upper limit voltage reached 4.25 V. After the upper limit voltage of 4.25 V was reached, the lithium ion secondary battery was charged at a constant voltage until 2.5 hours had elapsed since the start of charging. The lithium ion secondary battery was then discharged at a constant current of 30 mA until the lower limit voltage of 2.5 V was reached.

　この出願は、２０２４年３月２９日に出願された日本出願特願２０２４－０５７０８２号を基礎とする優先権を主張し、その開示の全てをここに取り込む。 This application claims priority based on Japanese Patent Application No. 2024-057082, filed March 29, 2024, the disclosure of which is incorporated herein in its entirety.

１　正極活物質層
２　負極活物質層
３　正極集電体
４　負極集電体
５　セパレータ
６　外装体
７　外装体
８　負極タブ
９　正極タブ
１０　リチウムイオン二次電池 REFERENCE SIGNS LIST 1 Positive electrode active material layer 2 Negative electrode active material layer 3 Positive electrode current collector 4 Negative electrode current collector 5 Separator 6 Exterior body 7 Exterior body 8 Negative electrode tab 9 Positive electrode tab 10 Lithium ion secondary battery

Claims (23)

　正極活物質層を含む正極と、負極活物質層を含む負極と、電解液と、を含む、リチウムイオン二次電池であって、
　前記負極活物質層に含まれる負極活物質は、表面の少なくとも一部にＳＥＩ膜を有し、
　前記電解液は、リチウムビス（フルオロスルホニル）イミドを含み、
　下記＜方法１＞による、前記電解液中の前記リチウムビス（フルオロスルホニル）イミドの濃度は、０．６質量％以上である、リチウムイオン二次電池。
＜方法１＞
　前記リチウムイオン二次電池を不活性ガス雰囲気下で分解し、次いで、分解した前記リチウムイオン二次電池から採取した０．２ｇの前記電解液を、１．０ｇの重アセトニトリルに溶解させて第１サンプルを作製し、次いで、基準物質として０．００２ｇの六フッ化ベンゼンを前記第１サンプルに添加して第２サンプルを作製し、次いで、０．５ｇの前記第２サンプルを用いて、１９Ｆ－ＮＭＲ法により、前記第２サンプル中の前記リチウムビス（フルオロスルホニル）イミドの量を測定し、次いで、前記第２サンプル中の前記リチウムビス（フルオロスルホニル）イミドの量から前記第１サンプル中の前記リチウムビス（フルオロスルホニル）イミドの濃度を算出し、下記式（１）から前記電解液中の前記リチウムビス（フルオロスルホニル）イミドの濃度を算出する。
式（１）：前記電解液中の前記リチウムビス（フルオロスルホニル）イミドの濃度＝（前記第１サンプル中の前記リチウムビス（フルオロスルホニル）イミドの量）／（分解した前記リチウムイオン二次電池から採取した前記電解液の量）×１００。 A lithium ion secondary battery comprising: a positive electrode including a positive electrode active material layer; a negative electrode including a negative electrode active material layer; and an electrolyte solution,
the negative electrode active material contained in the negative electrode active material layer has an SEI film on at least a part of its surface,
the electrolyte solution contains lithium bis(fluorosulfonyl)imide;
A lithium ion secondary battery according to the following <Method 1>, wherein the concentration of the lithium bis(fluorosulfonyl)imide in the electrolyte solution is 0.6 mass % or more.
<Method 1>
The lithium ion secondary battery was disassembled under an inert gas atmosphere, and then 0.2 g of the electrolyte solution collected from the disassembled lithium ion secondary battery was dissolved in 1.0 g of deuterated acetonitrile to prepare a first sample. Next, 0.002 g of hexafluorobenzene was added to the first sample as a reference substance to prepare a second sample. Next, using 0.5 g of the second sample, the amount of lithium bis(fluorosulfonyl)imide in the second sample was measured by a 19 F-NMR method. Next, the concentration of lithium bis(fluorosulfonyl)imide in the first sample was calculated from the amount of lithium bis(fluorosulfonyl)imide in the second sample, and the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte solution was calculated using the following formula (1):
Equation (1): Concentration of the lithium bis(fluorosulfonyl)imide in the electrolyte solution=(Amount of the lithium bis(fluorosulfonyl)imide in the first sample)/(Amount of the electrolyte solution collected from the disassembled lithium ion secondary battery)×100. 　前記負極活物質は、負極活物質（Ａ）と、前記負極活物質（Ａ）とは異なる種類の負極活物質（Ｂ）と、を含む、請求項１に記載のリチウムイオン二次電池。 The lithium-ion secondary battery of claim 1, wherein the negative electrode active material includes a negative electrode active material (A) and a negative electrode active material (B) of a type different from the negative electrode active material (A). 　前記負極活物質（Ａ）の、レーザー回折散乱法による体積基準のメジアン径Ｄ５０は、３．０μｍ以上３０．０μｍ以下であり、
　前記負極活物質（Ｂ）の、レーザー回折散乱法による体積基準のメジアン径Ｄ５０は、１．０μｍ以上２０．０μｍ以下である、請求項２に記載のリチウムイオン二次電池。 The negative electrode active material (A) has a volume-based median diameter D50 measured by a laser diffraction scattering method of 3.0 μm or more and 30.0 μm or less,
The lithium ion secondary battery according to claim 2 , wherein the negative electrode active material (B) has a volume-based median diameter D 50 of 1.0 μm or more and 20.0 μm or less, as measured by a laser diffraction scattering method. 　前記負極活物質（Ａ）は黒鉛粉末を含む、請求項２または３に記載のリチウムイオン二次電池。 The lithium-ion secondary battery according to claim 2 or 3, wherein the negative electrode active material (A) contains graphite powder. 　前記黒鉛粉末は、黒鉛粉末（Ａ１）と、レーザー回折散乱法による体積基準のメジアン径Ｄ５０が前記黒鉛粉末（Ａ１）とは異なる黒鉛粉末（Ａ２）と、を含み、
　前記黒鉛粉末（Ａ１）のメジアン径Ｄ５０は、前記黒鉛粉末（Ａ２）のメジアン径Ｄ５０より大きい、請求項４に記載のリチウムイオン二次電池。 The graphite powder comprises graphite powder (A1) and graphite powder (A2) having a volume-based median diameter D50 measured by a laser diffraction scattering method that is different from that of the graphite powder (A1),
The lithium ion secondary battery according to claim 4, wherein the median diameter D50 of the graphite powder (A1) is larger than the median diameter D50 of the graphite powder (A2). 　前記黒鉛粉末（Ａ１）は、表面に非晶質炭素を含む黒鉛粒子を含む、請求項５に記載のリチウムイオン二次電池。 The lithium-ion secondary battery described in claim 5, wherein the graphite powder (A1) includes graphite particles having amorphous carbon on the surface. 　前記黒鉛粉末（Ａ２）は、表面に非晶質炭素を含まない黒鉛粒子を含む、請求項５または６に記載のリチウムイオン二次電池。 The lithium-ion secondary battery described in claim 5 or 6, wherein the graphite powder (A2) contains graphite particles that do not contain amorphous carbon on the surface. 　前記黒鉛粉末（Ａ１）の前記メジアン径Ｄ５０は、５．０μｍ以上３０．０μｍ以下である、請求項５～７のいずれかに記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 5 to 7, wherein the median diameter D50 of the graphite powder (A1) is 5.0 µm or more and 30.0 µm or less. 　前記黒鉛粉末（Ａ２）の前記メジアン径Ｄ５０は、１．０μｍ以上２０．０μｍ以下である、請求項５～８のいずれかに記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 5 to 8, wherein the median diameter D50 of the graphite powder (A2) is 1.0 µm or more and 20.0 µm or less. 　前記黒鉛粉末（Ａ１）のメジアン径Ｄ５０をＤ１、前記黒鉛粉末（Ａ２）のメジアン径Ｄ５０をＤ２とそれぞれしたときに、Ｄ１に対するＤ２の比Ｄ２／Ｄ１の値は、０．４０以上１．０未満である、請求項５～９のいずれかに記載のリチウムイオン二次電池。 10. The lithium ion secondary battery according to any one of claims 5 to 9 , wherein the median diameter D50 of the graphite powder (A1) is D1 and the median diameter D50 of the graphite powder (A2) is D2 , and the ratio D2 / D1 of D2 to D1 is 0.40 or more and less than 1.0. 　前記負極活物質（Ａ）中の前記黒鉛粉末（Ａ１）の含有量は、前記負極活物質（Ａ）中の前記黒鉛粉末（Ａ２）の含有量を１００質量部としたときに、５０質量部以上２００質量部以下である、請求項５～１０のいずれかに記載のリチウムイオン二次電池。 The lithium-ion secondary battery according to any one of claims 5 to 10, wherein the content of the graphite powder (A1) in the negative electrode active material (A) is 50 parts by mass or more and 200 parts by mass or less, relative to 100 parts by mass of the content of the graphite powder (A2) in the negative electrode active material (A). 　前記負極活物質（Ｂ）は、酸化ケイ素粒子、並びにシリコンおよび炭素材料を含むＳｉ－Ｃ複合粒子からなる群から選択される一種または二種以上を含む、請求項２～１１のいずれかに記載のリチウムイオン二次電池。 The lithium-ion secondary battery according to any one of claims 2 to 11, wherein the negative electrode active material (B) comprises one or more particles selected from the group consisting of silicon oxide particles and Si-C composite particles containing silicon and a carbon material. 　前記Ｓｉ－Ｃ複合粒子は、前記炭素材料が多孔質炭素材料を含み、かつ、前記シリコンが前記多孔質炭素材料の細孔内の少なくとも一部に存在する、請求項１２に記載のリチウムイオン二次電池。 The lithium-ion secondary battery described in claim 12, wherein the Si-C composite particles contain a porous carbon material as the carbon material, and the silicon is present in at least some of the pores of the porous carbon material. 　前記Ｓｉ－Ｃ複合粒子の、レーザー回折散乱法による体積基準のメジアン径Ｄ５０は、１．０μｍ以上１６．０μｍ以下である、請求項１２または１３に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 12 or 13, wherein the Si—C composite particles have a volume-based median diameter D 50 of 1.0 μm or more and 16.0 μm or less, as measured by a laser diffraction scattering method. 　前記負極活物質層中の前記負極活物質（Ａ）の含有量は、前記負極活物質層の全量を１００質量部としたときに、５０質量部以上９９質量部以下である、請求項２～１４のいずれかに記載のリチウムイオン二次電池。 The lithium-ion secondary battery according to any one of claims 2 to 14, wherein the content of the negative electrode active material (A) in the negative electrode active material layer is 50 parts by mass or more and 99 parts by mass or less, when the total amount of the negative electrode active material layer is 100 parts by mass. 　前記負極活物質層中の前記負極活物質（Ｂ）の含有量は、前記負極活物質層の全量を１００質量部としたときに、１質量部以上５０質量部以下である、請求項２～１５のいずれかに記載のリチウムイオン二次電池。 The lithium-ion secondary battery according to any one of claims 2 to 15, wherein the content of the negative electrode active material (B) in the negative electrode active material layer is 1 part by mass or more and 50 parts by mass or less, when the total amount of the negative electrode active material layer is 100 parts by mass. 　前記負極活物質層中の前記負極活物質（Ａ）の含有量をＷＡ、前記負極活物質層中の前記負極活物質（Ｂ）の含有量をＷＢとそれぞれしたときに、ＷＢに対するＷＡの比ＷＡ／ＷＢの値は、１．０以上２０．０以下である、請求項２～１６のいずれかに記載のリチウムイオン二次電池。 17. The lithium ion secondary battery according to claim 2, wherein when the content of the negative electrode active material (A) in the negative electrode active material layer is W A and the content of the negative electrode active material ( B) in the negative electrode active material layer is W B , a ratio of W A to W B , W A /W B , is 1.0 or more and 20.0 or less. 　前記正極活物質層に含まれる正極活物質は、リチウム－ニッケル－コバルト－マンガン複合酸化物の単結晶により構成される粒子（Ｃ１）、およびリチウム－ニッケル－コバルト－マンガン複合酸化物の多結晶により構成される粒子（Ｃ２）から選択される一種または二種以上を含む粒子（Ｃ）を含む、請求項１～１７のいずれかに記載のリチウムイオン二次電池。 The lithium-ion secondary battery of any one of claims 1 to 17, wherein the positive electrode active material contained in the positive electrode active material layer includes particles (C) containing one or more types selected from particles (C1) composed of a single crystal of lithium-nickel-cobalt-manganese composite oxide and particles (C2) composed of a polycrystal of lithium-nickel-cobalt-manganese composite oxide. 　前記粒子（Ｃ）中のニッケルの含有量は、ニッケル、コバルト、およびマンガンの含有量の合計を１００ｍｏｌとしたときに、８０ｍｏｌ以上である、請求項１８に記載のリチウムイオン二次電池。 The lithium-ion secondary battery of claim 18, wherein the content of nickel in the particles (C) is 80 mol or more when the total content of nickel, cobalt, and manganese is 100 mol. 　前記粒子（Ｃ）中のニッケル、コバルト、およびマンガンのそれぞれの含有量は、前記粒子（Ｃ）中のニッケル、コバルト、およびマンガンの含有量の合計を１００ｍｏｌとしたときに、ニッケルの含有量は８０ｍｏｌ以上９９ｍｏｌ以下であり、コバルトの含有量は０．５ｍｏｌ以上１０ｍｏｌ以下であり、かつマンガンの含有量は０．５ｍｏｌ以上１０ｍｏｌ以下である、請求項１８または１９に記載のリチウムイオン二次電池。 The lithium ion secondary battery of claim 18 or 19, wherein the respective contents of nickel, cobalt, and manganese in the particles (C) are such that, when the total content of nickel, cobalt, and manganese in the particles (C) is 100 mol, the nickel content is 80 mol or more and 99 mol or less, the cobalt content is 0.5 mol or more and 10 mol or less, and the manganese content is 0.5 mol or more and 10 mol or less. 　下記の＜方法２＞による、２５℃での容量維持率Ｒ２５は、８７．０％以上である、請求項１～２０のいずれかに記載のリチウムイオン二次電池。
＜方法２＞
　前記リチウムイオン二次電池を２５℃の恒温槽内に配置し、次いで、下記＜充放電サイクル＞によって前記リチウムイオン二次電池の充放電を行い、１回目の放電容量を測定し、次いで、下記＜充放電サイクル＞によって前記リチウムイオン二次電池の充放電を合計４９９回になるまで繰り返し、次いで、下記＜充放電サイクル＞によって前記リチウムイオン二次電池の充放電を行い、５００回目の放電容量を測定し、次いで、下記式（２）から前記容量維持率Ｒ２５を算出する。
式（２）：前記容量維持率Ｒ２５＝（前記５００回目の放電容量）／（前記１回目の放電容量）×１００
＜充放電サイクル＞
　上限電圧４．２５Ｖに達するまで３０ｍＡで前記リチウムイオン二次電池を充電し、次いで、前記上限電圧４．２５Ｖに達した後は、充電を開始してからの経過時間が２．５時間になるまで、前記リチウムイオン二次電池を定電圧で充電し、次いで、下限電圧２．５Ｖに達するまで３０ｍＡの定電流で前記リチウムイオン二次電池を放電する。 The lithium ion secondary battery according to any one of claims 1 to 20, wherein the capacity retention rate R 25 at 25°C according to the following <Method 2> is 87.0% or more.
<Method 2>
The lithium ion secondary battery is placed in a thermostatic chamber at 25°C, and then the lithium ion secondary battery is charged and discharged in accordance with the <charge and discharge cycle> described below, and the first discharge capacity is measured. Next, the lithium ion secondary battery is repeatedly charged and discharged in accordance with the <charge and discharge cycle> described below until a total of 499 cycles have been reached. Next, the lithium ion secondary battery is charged and discharged in accordance with the <charge and discharge cycle> described below, and the discharge capacity is measured for the 500th cycle. Next, the capacity retention rate R25 is calculated using the following formula (2).
Formula (2): Capacity retention rate R 25 =(500th discharge capacity)/(1st discharge capacity)×100
<Charge/discharge cycle>
The lithium ion secondary battery is charged at 30 mA until an upper limit voltage of 4.25 V is reached, and then, after the upper limit voltage of 4.25 V is reached, the lithium ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging, and then, the lithium ion secondary battery is discharged at a constant current of 30 mA until a lower limit voltage of 2.5 V is reached. 　前記リチウムイオン二次電池中の前記電解液の含有量は、前記負極活物質の含有量と前記正極活物質層に含まれる正極活物質の含有量との合計を１００質量部としたときに、１５質量部以上６０質量部以下である、請求項１～２１のいずれかに記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 21, wherein the content of the electrolyte in the lithium ion secondary battery is 15 parts by mass or more and 60 parts by mass or less, when the sum of the content of the negative electrode active material and the content of the positive electrode active material contained in the positive electrode active material layer is 100 parts by mass. 　請求項１～２２のいずれかに記載のリチウムイオン二次電池を備える、リチウムイオン二次電池モジュール。 A lithium ion secondary battery module comprising the lithium ion secondary battery according to any one of claims 1 to 22.
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WO2023008177A1 (en) * 2021-07-30 2023-02-02 パナソニックＩｐマネジメント株式会社 Negative electrode for secondary battery, and secondary battery
WO2023171564A1 (en) * 2022-03-09 2023-09-14 パナソニックエナジ－株式会社 Nonaqueous electrolytic solution secondary battery

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WO2023008177A1 (en) * 2021-07-30 2023-02-02 パナソニックＩｐマネジメント株式会社 Negative electrode for secondary battery, and secondary battery
WO2023171564A1 (en) * 2022-03-09 2023-09-14 パナソニックエナジ－株式会社 Nonaqueous electrolytic solution secondary battery

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