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WO2024181064A1 - Liant pour batterie secondaire au lithium-ion, électrode négative pour batterie secondaire au lithium-ion, et batterie secondaire au lithium-ion - Google Patents

Liant pour batterie secondaire au lithium-ion, électrode négative pour batterie secondaire au lithium-ion, et batterie secondaire au lithium-ion Download PDF

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Publication number
WO2024181064A1
WO2024181064A1 PCT/JP2024/004066 JP2024004066W WO2024181064A1 WO 2024181064 A1 WO2024181064 A1 WO 2024181064A1 JP 2024004066 W JP2024004066 W JP 2024004066W WO 2024181064 A1 WO2024181064 A1 WO 2024181064A1
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Prior art keywords
chemical formula
negative electrode
binder
ion secondary
active material
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PCT/JP2024/004066
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English (en)
Japanese (ja)
Inventor
敦志 門田
友美 岩本
優花 増田
亮介 木戸
浩 笹川
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TDK Corp
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TDK Corp
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    • 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
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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

  • the present invention relates to a binder for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery.
  • Lithium-ion secondary batteries are also widely used as a power source for mobile devices such as mobile phones and laptops, as well as hybrid cars.
  • the capacity of a lithium-ion secondary battery depends mainly on the active material of the electrodes.
  • Graphite is generally used as the negative electrode active material, but there is a demand for negative electrode active materials with higher capacity. For this reason, silicon (Si), which has a theoretical capacity far greater than that of graphite (372 mAh/g), has attracted attention.
  • Anode active materials that contain Si undergo a large volume expansion during charging. This volume expansion of the cathode active material causes a decrease in the cycle characteristics of the battery.
  • the anode active material expands in volume, for example, the conductive paths between the anode active materials are cut, peeling occurs at the interface between the anode active material layer and the current collector, cracks occur in the SEI (Solid Electrolyte Interphase) coating, and electrolyte decomposition occurs. These reduce the cycle characteristics of the battery.
  • Patent Document 1 discloses a lithium ion secondary battery that uses polyacrylic acid as a binder.
  • This disclosure has been made in consideration of the above problems, and aims to provide a configuration that can improve the cycle characteristics of lithium-ion secondary batteries.
  • the binder for lithium ion secondary batteries according to the first aspect has a polyacrylic acid compound having, as a unit structure, the following chemical formula (1) and at least one of chemical formulas (2) and (3).
  • R is either H or CH3
  • X1 is any selected from the group consisting of O, OCH2 , NH, and NCH3
  • X2 is any selected from the group consisting of an aromatic ring having 6 to 16 carbon atoms, an alkyl group having 2 to 18 carbon atoms, a polyethylene oxide having 5 to 35 carbon atoms, a polypropylene oxide having 7 to 37 carbon atoms, and a polyethyleneimine having 5 to 35 carbon atoms, or any of these partially substituted with a substituting element.
  • the molar ratio of the chemical formula (1) is 60% or more and 90% or less
  • the molar ratio of the chemical formula (2) is 0% or more and 20% or less
  • the molar ratio of the chemical formula (3) is 0% or more and 30% or less.
  • This binder for lithium ion secondary batteries has a ratio of weight average molecular weight to number average molecular weight measured by gel permeation chromatography of 1.5 or more and 6.0 or less.
  • the negative electrode for a lithium ion secondary battery according to the second aspect includes the binder for a lithium ion secondary battery according to the above aspect and a negative electrode active material containing Si.
  • a lithium ion secondary battery according to a third aspect has a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is a negative electrode for a lithium ion secondary battery according to the above aspect.
  • the lithium ion secondary battery according to the above embodiment has excellent cycle characteristics.
  • FIG. 1 is a schematic diagram of a lithium ion secondary battery according to a first embodiment
  • FIG. 2 is a schematic diagram of a binder according to the first embodiment.
  • Fig. 1 is a schematic diagram of a lithium ion secondary battery according to a first embodiment.
  • the lithium ion secondary battery 100 shown in Fig. 1 includes a power generating element 40, an exterior body 50, and a non-aqueous electrolyte (not shown).
  • the exterior body 50 covers the periphery of the power generating element 40.
  • the power generating element 40 is connected to the outside via a pair of terminals 60, 62 connected to the power generating element 40.
  • the non-aqueous electrolyte is contained in the exterior body 50.
  • Fig. 1 illustrates a case in which one power generating element 40 is provided in the exterior body 50, a plurality of power generating elements 40 may be stacked.
  • the power generating element 40 includes a separator 10 , a positive electrode 20 , and a negative electrode 30 .
  • the positive electrode 20 includes, for example, a positive electrode current collector 22 and a positive electrode active material layer 24.
  • the positive electrode active material layer 24 is in contact with at least one surface of the positive electrode current collector 22.
  • the positive electrode current collector 22 is, for example, a conductive plate material.
  • the positive electrode current collector 22 is, for example, a thin metal plate of aluminum, copper, nickel, titanium, stainless steel, or the like. Aluminum, which is light in weight, is preferably used for the positive electrode current collector 22.
  • the average thickness of the positive electrode current collector 22 is, for example, 10 ⁇ m or more and 30 ⁇ m or less.
  • the positive electrode active material layer 24 contains, for example, a positive electrode active material.
  • the positive electrode active material layer 24 may contain a conductive assistant and a binder as necessary.
  • the positive electrode active material includes an electrode active material that can reversibly absorb and release lithium ions, remove and insert lithium ions (intercalation), or dope and dedope lithium ions and counter anions.
  • the positive electrode active material is, for example, a composite metal oxide.
  • the positive electrode active material may be a lithium-free material.
  • the lithium-free material include FeF 3 , conjugated polymers containing organic conductive materials, Chevrel phase compounds, transition metal chalcogenides, vanadium oxides, and niobium oxides.
  • the lithium-free material may be any one of the materials or a combination of a plurality of materials.
  • discharge is performed first. Lithium is inserted into the positive electrode active material by discharging.
  • lithium may be pre-doped chemically or electrochemically into the lithium-free positive electrode active material.
  • the conductive additive increases the electronic conductivity between the positive electrode active materials.
  • the conductive additive is, for example, carbon powder, carbon nanotubes, carbon material, metal powder, a mixture of carbon material and metal powder, or conductive oxide.
  • the carbon powder is, for example, carbon black, acetylene black, ketjen black, etc.
  • the metal powder is, for example, copper, nickel, stainless steel, iron, etc. powder.
  • the content of the conductive additive in the positive electrode active material layer 24 is not particularly limited.
  • the content of the conductive additive relative to the total mass of the positive electrode active material, the conductive additive, and the binder is 0.5% by mass or more and 20% by mass or less, and preferably 1% by mass or more and 5% by mass or less.
  • the binder in the positive electrode active material layer 24 binds the positive electrode active material together. Any known binder can be used.
  • the binder may be the same as that used in the negative electrode active material layer 34 described later.
  • the binder is preferably one that does not dissolve in the electrolyte, has oxidation resistance, and has adhesive properties.
  • the binder is, for example, a fluororesin.
  • the binder is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamideimide (PAI), polybenzimidazole (PBI), polyethersulfone (PES), polyacrylic acid and its copolymers, metal ion crosslinked polyacrylic acid and its copolymers, polypropylene (PP) or polyethylene (PE) grafted with maleic anhydride, or a mixture thereof.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PA polyamide
  • PI polyimide
  • PAI polyamideimide
  • PBI polybenzimidazole
  • PES polyethersulfone
  • PVDF polyacrylic acid and its copolymers
  • metal ion crosslinked polyacrylic acid and its copolymers polypropylene (PP) or polyethylene (PE) grafted with maleic anhydride, or a
  • the binder content in the positive electrode active material layer 24 is not particularly limited.
  • the binder content relative to the total mass of the positive electrode active material, conductive additive, and binder is 1 mass% or more and 15 mass% or less, and preferably 1.5 mass% or more and 5 mass% or less. If the binder content is low, the adhesive strength of the positive electrode 20 will be weakened. If the binder content is high, the binder is electrochemically inactive and does not contribute to the discharge capacity, so the energy density of the lithium ion secondary battery 100 will be low.
  • the negative electrode 30 includes, for example, a negative electrode current collector 32 and a negative electrode active material layer 34.
  • the negative electrode active material layer 34 is formed on at least one surface of the negative electrode current collector 32.
  • the negative electrode current collector 32 is, for example, a conductive plate material.
  • the negative electrode current collector 32 may be the same as the positive electrode current collector 22.
  • the negative electrode active material layer 34 contains a negative electrode active material and a binder.
  • the negative electrode active material layer 34 may contain a conductive assistant as necessary.
  • the negative electrode active material includes, for example, silicon or a silicon compound.
  • the silicon compound is, for example, a silicon alloy, silicon oxide, etc.
  • the silicon or silicon compound may be crystalline or amorphous.
  • Amorphous silicon or silicon compound can be produced by a melt-spun method, a gas atomization method, etc.
  • the negative electrode active material may be an active material other than a silicon-based material.
  • the silicon alloy is represented by XnSi.
  • X is a cation.
  • X is, for example, Ba, Mg, Al, Zn, Sn, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Y, Zr, Nb, Mo, W, Au, Ti, Na, K, etc.
  • n satisfies 0 ⁇ n ⁇ 0.5.
  • Silicon oxide is represented by SiO x . x satisfies, for example, 0.8 ⁇ x ⁇ 2.
  • Silicon oxide may be composed of only SiO 2 , may be composed of only SiO, or may be a mixture of SiO and SiO 2. Silicon oxide may also be partially deficient in oxygen.
  • the negative electrode active material may be a composite of silicon or a silicon compound.
  • the composite is a silicon or silicon compound particle having at least a part of its surface coated with a conductive material.
  • the conductive material is, for example, a carbon material, Al, Ti, Fe, Ni, Cu, Zn, Ag, Sn, etc.
  • a silicon carbon composite material Si-C
  • the amount of conductive material coated on the silicon or silicon compound particle is, for example, 0.01% by mass to 30% by mass, and preferably 0.1% by mass to 20% by mass, based on the total mass of the composite.
  • the composite can be produced, for example, by mechanical alloying, chemical vapor deposition, wet method, or a method of coating a polymer and then pyrolyzing the polymer to carbonize it.
  • the specific surface area of the negative electrode active material determined by the BET method is, for example, 0.5 m 2 /g or more and 100 m 2 /g or less, and preferably 1.0 m 2 /g or more and 20 m 2 /g or less. If the specific surface area is small, Li ions are difficult to insert and remove between the negative electrode active material. If the specific surface area is large, a large amount of binder is required to form an electrode, and the capacity per unit volume is small.
  • the binder in the negative electrode active material layer 34 binds the negative electrode active materials together.
  • the binder has a polyacrylic acid compound having at least one of the following chemical formulas (1), (2), and (3) as a unit structure.
  • R is either H or CH3
  • X1 is any selected from the group consisting of O, OCH2 , NH, and NCH3
  • X2 is any selected from the group consisting of an aromatic ring having 6 to 16 carbon atoms, an alkyl group having 2 to 18 carbon atoms, a polyethylene oxide having 5 to 35 carbon atoms, a polypropylene oxide having 7 to 37 carbon atoms, and a polyethyleneimine having 5 to 35 carbon atoms, or any of these partially substituted with a substituting element.
  • the content of the polyacrylic acid compound in the binder may be, in mass ratio, 20% to 100%, 50% to 100%, or 90% to 100%.
  • the bonds of the unit structures may be random, and the order of bonds of chemical formula (1), chemical formula (2), and chemical formula (3) does not matter.
  • Chemical formula (1) is a required unit structure. It is sufficient for the compound to have at least one of the unit structures of chemical formula (2) and chemical formula (3), and it may have both unit structures.
  • the molar ratio of chemical formula (1) is 60% or more and 90% or less
  • the molar ratio of chemical formula (2) is 0% or more and 20% or less
  • the molar ratio of chemical formula (3) is 0% or more and 30% or less.
  • FIG. 2 is a schematic diagram of the binder for lithium ion secondary batteries according to this embodiment.
  • the binder has, for example, a main chain 1, and a branched chain 2 and a branched chain 3 branched from the main chain 1.
  • the branched chain 2 branches outward from the main chain 1, and the branched chain 3 branches inward from the main chain 1.
  • the branched chain 2 contains more COOLi and COOH of the unit structures represented by chemical formulas (1) and (2)
  • the branched chain 3 contains more COX 1 X 2 of the unit structure represented by chemical formula (3).
  • the unit structures represented by chemical formulas (1) and (2) are highly water-soluble, and the unit structure represented by chemical formula (3) is highly fat-soluble.
  • the polymer constituting the binder has a structure similar to that of a surfactant as a whole, and is prone to a micelle structure in which the fat-soluble COX 1 X 2 is on the inside and the water-soluble COOLi and COOH are on the outside.
  • a micelle structure is formed in which the inner structure and the outer structure are reversed.
  • COOLi and COOH are the parts responsible for binding with the active material, and their presence can enhance the binding between the active material and the binder.
  • the polymer wraps around the fat-soluble COX 1 X 2 inside and forms a compactly aggregated structure, it is possible to suppress excessive coverage of the binder on the surface of the active material.
  • the binder also has a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) measured by gel permeation chromatography (GPC) of 1.5 or more and 6.0 or less.
  • Gel permeation chromatography is a type of high performance liquid chromatography (HPLC). Gel permeation chromatography can separate polymers based on molecular size (volume).
  • the number average molecular weight represents the simple average of the molecular weight of each polymer chain contained in the polymer, while the weight average molecular weight represents how large the molecular weight of molecules is present in a collection of polymers.
  • the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) is within the above range, the degree of variation in molecular weight per polymer is appropriate.
  • a small ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) means that the molecular weight distribution of the polymers that make up the binder is narrow.
  • the binder is made up of polymers of similar size.
  • a large ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) means that the molecular weight distribution of the polymers that make up the binder is wide.
  • the binder contains a variety of polymers with different molecular weights.
  • the proportion of low-molecular-weight polymers among the polymers that make up the binder is appropriate.
  • the low-molecular-weight polymers penetrate into the gaps between the active materials and between the active materials and the current collector foil, improving the adhesion between them.
  • the polymers will penetrate into these gaps appropriately.
  • the low-molecular-weight polymers will completely fill the gaps between the active materials and between the active materials and the current collector foil, preventing a decrease in battery capacity.
  • the binder content in the negative electrode active material layer 34 is not particularly limited.
  • the binder content relative to the total mass of the negative electrode active material, conductive additive, and binder is 1 mass% or more and 20 mass% or less, and preferably 3 mass% or more and 15 mass% or less. If the binder content is low, the adhesive strength between the negative electrode active materials in the negative electrode 30 and the adhesive strength between the negative electrode 30 and the binder will be weakened. If the binder content is high, the binder is electrochemically inactive and does not contribute to the discharge capacity, resulting in a low energy density of the lithium ion secondary battery 100.
  • the conductive additive in the negative electrode active material layer 34 enhances the electronic conductivity between the negative electrode active materials.
  • the conductive additive can be the same as that in the positive electrode active material layer 24.
  • the content of the conductive additive in the negative electrode active material layer 34 is not particularly limited.
  • the content of the conductive additive relative to the total mass of the negative electrode active material, the conductive additive, and the binder is 5% by mass or more and 20% by mass or less, and preferably 1% by mass or more and 12% by mass or less.
  • the separator 10 is sandwiched between the positive electrode 20 and the negative electrode 30.
  • the separator 10 separates the positive electrode 20 from the negative electrode 30 and prevents a short circuit between the positive electrode 20 and the negative electrode 30.
  • the separator 10 extends in-plane along the positive electrode 20 and the negative electrode 30. Lithium ions can pass through the separator 10.
  • the separator 10 has, for example, an electrically insulating porous structure.
  • the separator 10 is, for example, a monolayer or laminate of a polyolefin film.
  • the separator 10 may be a stretched film of a mixture of polyethylene, polypropylene, etc.
  • the separator 10 may be a fibrous nonwoven fabric made of at least one constituent material selected from the group consisting of cellulose, polyester, polyacrylonitrile, polyamide, polyethylene, and polypropylene.
  • the separator 10 may be, for example, a solid electrolyte.
  • the solid electrolyte is, for example, a polymer solid electrolyte, an oxide-based solid electrolyte, or a sulfide-based solid electrolyte.
  • the separator 10 may be an inorganic-coated separator.
  • the inorganic-coated separator is formed by applying a mixture of a resin such as PVDF or CMC and an inorganic material such as alumina or silica to the surface of the above-mentioned film.
  • the inorganic-coated separator has excellent heat resistance and suppresses the deposition of transition metals eluted from the positive electrode on the negative electrode surface.
  • the electrolytic solution is sealed in the exterior body 50 and impregnates the power generating element 40.
  • the non-aqueous electrolytic solution includes, for example, a non-aqueous solvent and an electrolytic salt.
  • the electrolytic salt is dissolved in the non-aqueous solvent.
  • a known electrolyte solution can be used as the electrolyte solution.
  • the electrolyte solution contains, for example, a non-aqueous solvent and an electrolyte salt.
  • the electrolytic salt is, for example, a lithium salt.
  • the electrolyte is, for example, LiPF6 , LiClO4 , LiBF4 , LiCF3SO3 , LiCF3CF2SO3, LiC(CF3SO2)3, LiN(CF3SO2)2, LiN(CF3CF2SO2 ) 2 , LiN ( CF3SO2 ) ( C4F9SO2 ) , LiN ( CF3CF2CO ) 2 , LiBOB, LiN( FSO2 ) 2 , etc.
  • the lithium salt may be used alone or in combination of two or more. From the viewpoint of the degree of ionization , it is preferable that the electrolyte contains LiPF6 .
  • the non-aqueous solvent is, for example, an aprotic organic solvent.
  • the organic solvent is, for example, a cyclic carbonate, a chain carbonate, an ether, a mixture thereof, etc.
  • the cyclic carbonate solvates the electrolyte.
  • the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and fluoroethylene carbonate.
  • the cyclic carbonate preferably contains at least fluoroethylene carbonate.
  • Fluoroethylene carbonate (FEC) has a high redox potential and is easily reduced and decomposed. By reducing and decomposing a portion of the fluoroethylene carbonate (FEC), the electrolyte in the electrolyte and the remaining solvent become less likely to decompose.
  • fluoroethylene carbonate (FEC) forms a thin and stable coating (SEI coating) on the entire surface of the negative electrode active material at the beginning of use of the lithium ion secondary battery. The SEI coating prevents direct contact between the negative electrode active material and the electrolyte, and prevents the electrolyte from decomposing.
  • the chain carbonate reduces the viscosity of the cyclic carbonate.
  • Examples of the chain carbonate are diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.
  • the non-aqueous solvent may also contain other solvents such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone, 1,2-dimethoxyethane, and 1,2-diethoxyethane.
  • the power generating element 40 and the non-aqueous electrolyte are sealed inside the exterior body 50.
  • the exterior body 50 prevents the non-aqueous electrolyte from leaking to the outside and prevents moisture and the like from entering the lithium ion secondary battery 100 from the outside.
  • the exterior body 50 has a metal foil 52 and a resin layer 54 laminated on each side of the metal foil 52.
  • the exterior body 50 is a metal laminate film in which the metal foil 52 is coated on both sides with a polymer film (resin layer 54).
  • the metal foil 52 may be, for example, aluminum foil.
  • the resin layer 54 may be a polymer film such as polypropylene.
  • the materials constituting the resin layer 54 may be different on the inside and outside.
  • the material for the outside may be a polymer with a high melting point, such as polyethylene terephthalate (PET) or polyamide (PA), and the material for the polymer film on the inside may be polyethylene (PE) or polypropylene (PP).
  • the terminals 60 and 62 are connected to the negative electrode 30 and the positive electrode 20, respectively.
  • the terminal 60 connected to the negative electrode 30 is a negative electrode terminal
  • the terminal 62 connected to the positive electrode 20 is a positive electrode terminal.
  • the terminals 60 and 62 are responsible for electrical connection to the outside.
  • the terminals 60 and 62 are made of a conductive material such as aluminum, nickel, or copper.
  • the connection method may be welding or screwing.
  • the terminals 60 and 62 are preferably protected with insulating tape to prevent short circuits.
  • the lithium ion secondary battery 100 is produced by preparing and assembling the negative electrode 30, the positive electrode 20, the separator 10, the electrolyte, and the exterior body 50. An example of a method for producing the lithium ion secondary battery 100 will be described below.
  • the negative electrode 30 is produced, for example, by carrying out a slurry production process, an electrode application process, a drying process, and a rolling process in that order.
  • the slurry preparation process is a process in which a negative electrode active material (silicon or silicon compound), a binder, a conductive assistant, and a solvent are mixed to prepare a slurry.
  • a binder a polyacrylic acid compound having at least one of chemical formula (1), chemical formula (2), and chemical formula (3) as a unit structure is used.
  • This polyacrylic acid compound can be prepared by polymerizing a monomer containing chemical formula (1), a monomer containing chemical formula (2), and a monomer containing chemical formula (3) in a predetermined molar ratio.
  • the ratio of the weight average molecular weight to the average molecular weight of the polyacrylic acid compound can be adjusted to 1.5 or more and 6.0 or less.
  • the solvent is, for example, water.
  • the composition ratio of the negative electrode active material, conductive additive, and binder is preferably 70 wt% to 99 wt%: 0 wt% to 10 wt%: 1 wt% to 20 wt% by mass. These mass ratios are adjusted so that the total is 100 wt%.
  • the negative electrode active material may be a composite obtained by mixing active material particles and a conductive material while applying shear force. When the active material particles are mixed with a shear force to the extent that the active material particles are not altered, the surfaces of the active material particles are coated with the conductive material.
  • the particle size of the negative electrode active material can be adjusted by adjusting the degree of mixing.
  • the negative electrode active material may also be sieved after preparation to make the particle size uniform.
  • the electrode coating process is a process of coating the surface of the negative electrode current collector 32 with a slurry.
  • a slurry There are no particular limitations on the method of coating the slurry.
  • the slit die coating method or the doctor blade method can be used as a method of coating the slurry.
  • the drying process is a process for removing the solvent from the slurry.
  • the negative electrode current collector 32 on which the slurry has been applied is dried in an atmosphere of 60°C or higher and 200°C or lower. Through this procedure, the negative electrode active material layer 34 is formed on the negative electrode current collector 32.
  • the rolling process is carried out as necessary.
  • the rolling process is a process in which pressure is applied to the negative electrode active material layer 34 to adjust the density of the negative electrode active material layer 34.
  • the rolling process is carried out, for example, with a roll press device or the like.
  • the positive electrode 20 can be produced in the same manner as the negative electrode 30.
  • the separator 10 and the exterior body 50 can be commercially available.
  • the prepared positive electrode 20 and negative electrode 30 are stacked so that the separator 10 is positioned between them to prepare the power generating element 40. If the power generating element 40 is a wound body, the positive electrode 20, the negative electrode 30, and one end side of the separator 10 are wound around the axis.
  • the power generating element 40 is enclosed in the exterior body 50.
  • the non-aqueous electrolyte is injected into the exterior body 50.
  • the pressure is reduced, heating, etc. is performed, so that the non-aqueous electrolyte is impregnated into the power generating element 40.
  • the exterior body 50 is sealed by applying heat, etc., to obtain the lithium-ion secondary battery 100. Note that instead of injecting the electrolyte into the exterior body 50, the power generating element 40 may be impregnated with the electrolyte.
  • the lithium ion secondary battery 100 according to the first embodiment has excellent cycle characteristics. This is believed to be because the binder and active material contained in the negative electrode active material layer 34 are bound together with high binding strength.
  • the binder according to this embodiment compactly aggregates and penetrates between the active materials and between the active materials and the current collecting foil, enhancing the binding strength between them.
  • Example 1 A positive electrode slurry was applied to one surface of an aluminum foil having a thickness of 15 ⁇ m.
  • the positive electrode slurry was prepared by mixing a positive electrode active material, a conductive assistant, a binder, and a solvent.
  • the positive electrode active material was Li x CoO 2.
  • the conductive assistant was acetylene black.
  • the binder was polyvinylidene fluoride (PVDF).
  • the solvent was N-methyl-2-pyrrolidone. 97 parts by mass of the positive electrode active material, 1 part by mass of the conductive assistant, 2 parts by mass of the binder, and 70 parts by mass of the solvent were mixed to prepare a positive electrode slurry.
  • the amount of the positive electrode active material carried in the positive electrode active material layer after drying was set to 25 mg/cm 2.
  • the solvent was removed from the positive electrode slurry in a drying furnace to prepare a positive electrode active material layer.
  • the positive electrode active material layer was pressed with a roll press to prepare a positive electrode.
  • negative electrode slurry was applied to one side of a 10 ⁇ m thick copper foil.
  • the negative electrode slurry was prepared by mixing a negative electrode active material, a conductive additive, a binder, and a solvent.
  • the negative electrode active material was silicon with a particle size of 3 ⁇ m. Carbon black was used as the conductive additive.
  • the binder was a polyacrylic acid compound containing the unit structure of chemical formula (1) and the unit structure of chemical formula (2). R in the unit structures of chemical formula (1) and chemical formula (2) was H.
  • the molar ratio of the unit structure of chemical formula (1) to the unit structure of chemical formula (2) was 90:10 (unit structure of chemical formula (1) : unit structure of chemical formula (2)).
  • the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polyacrylic acid compound was 3.6.
  • the above structure of the binder can be determined by extracting the binder from the prepared electrode and analyzing it.
  • the binder, -COOLi and -COOH, are highly water-soluble and can be easily extracted from the electrode.
  • Water was used as the solvent.
  • 90 parts by mass of the negative electrode active material, 5 parts by mass of the conductive assistant, and 5 parts by mass of the binder were mixed with water to prepare a negative electrode slurry.
  • the amount of the negative electrode active material carried in the negative electrode active material layer after drying was set to 2.5 mg/cm 2.
  • the solvent was removed from the negative electrode slurry in a drying furnace to prepare a negative electrode active material layer.
  • the negative electrode active material layer was pressed with a roll press, and then treated at 150° C. or higher for 5 hours in a nitrogen atmosphere and dried.
  • LiPF 6 was used as the electrolyte salt.
  • the concentration of LiPF 6 was 1 mol/L.
  • the prepared negative electrode and positive electrode were laminated with a separator (porous polyethylene sheet) between them so that the positive electrode active material layer and the negative electrode active material layer faced each other to obtain a laminate.
  • a nickel negative electrode lead was attached to the negative electrode of the laminate.
  • An aluminum positive electrode lead was attached to the positive electrode of the laminate.
  • the positive electrode lead and the negative electrode lead were welded by an ultrasonic welding machine.
  • This laminate was inserted into an exterior body of an aluminum laminate film and heat-sealed except for one place around the periphery to form a closed portion.
  • the above-mentioned electrolyte was injected into the exterior body, and the remaining one place was sealed by heat sealing while reducing the pressure with a vacuum sealer to produce a lithium ion secondary battery.
  • the battery was charged at a constant current of 0.5 C (a current value at which charging at a constant current of 25° C. is completed in 1 hour) at a constant current rate of 0.5 C (CC-CV charging) until the battery voltage reached 4.2 V, and then discharged at a constant current rate of 1.0 C until the battery voltage reached 2.5 V (CC discharge).
  • the discharge capacity after charging and discharging was detected to determine the battery capacity Q1 before the cycle test.
  • the battery whose battery capacity Q1 was determined above was charged again using a secondary battery charge/discharge tester at a constant current and constant voltage charge rate of 0.5 C until the battery voltage reached 4.2 V, and discharged at a constant current discharge rate of 1.0 C until the battery voltage reached 2.5 V.
  • the above charge/discharge was counted as one cycle, and 500 charge/discharge cycles were performed. Thereafter, the discharge capacity after the completion of 500 charge/discharge cycles was detected, and the battery capacity Q2 after 500 cycles was determined.
  • the capacity retention rate E after 500 cycles was calculated from the capacities Q1 and Q2 obtained above.
  • the capacity retention rate of Example 1 was 71%.
  • the battery capacity Q1 before the cycle test was divided by the weight of the negative electrode active material layer to obtain the capacity (mAh) per 1 g of the negative electrode active material layer.
  • Example 2 to 4 are different from Example 1 in that the binder used in the negative electrode was changed.
  • the binder in Examples 2 to 4 was a polyacrylic acid compound containing a unit structure of chemical formula (1), a unit structure of chemical formula (2), and a unit structure of chemical formula (3).
  • R in the unit structures of chemical formula (1), chemical formula (2), and chemical formula (3) was H.
  • X 1 in chemical formula (3) was an OCH 2 group, and X 2 was represented by chemical formula (4).
  • Examples 2 to 4 also differ in the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polyacrylic acid compound.
  • Example 5 differs from Example 2 in that the binder used in the negative electrode is changed.
  • the binder of Example 5 differs from Example 2 in that X2 in chemical formula (3) is represented by chemical formula (5).
  • Examples 6 and 7 are different from Example 2 in that the binder used in the negative electrode is changed.
  • the binders in Examples 6 and 7 are different from those in Example 2 in the molar ratio of the unit structures and X2 in chemical formula (3).
  • the unit structure of chemical formula (1): the unit structure of chemical formula (2): the unit structure of chemical formula (3) 80: 12: 8.
  • X2 in chemical formula (3) was represented by chemical formula (6).
  • the unit structure of chemical formula (1): the unit structure of chemical formula (2): the unit structure of chemical formula (3) 85: 8: 7.
  • X2 in chemical formula (3) was represented by chemical formula (7).
  • Examples 8 to 10 differ from Example 2 in that the binder used in the negative electrode was changed.
  • the binders of Examples 8 to 10 differ from Example 2 in the molar ratio of the unit structures and in that X1 in chemical formula (3) is O and X2 is represented by chemical formula (8).
  • Examples 8 to 10 also differ in the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polyacrylic acid compound.
  • Example 11 differs from Example 1 in that the binder used in the negative electrode was changed.
  • the binder in Example 11 was a polyacrylic acid compound containing a unit structure of chemical formula (1) and a unit structure of chemical formula (3).
  • R in the unit structures of chemical formula (1) and chemical formula (3) was CH3 .
  • X1 in chemical formula (3) was O, and X2 was represented by chemical formula (9).
  • the molar ratio of the unit structure of chemical formula (1) to the unit structure of chemical formula (3) was 92:8, i.e., the unit structure of chemical formula (1): the unit structure of chemical formula (3).
  • Example 12 differs from Example 1 in that the binder used in the negative electrode was changed.
  • R in the unit structures of chemical formula (1), chemical formula (2), and chemical formula (3) was CH3 .
  • X1 in chemical formula (3) was O, and X2 was represented by chemical formula (10).
  • Examples 13 to 15 differ from Example 2 in that the binder used in the negative electrode was changed.
  • the binders of Examples 13 to 15 differ from Example 2 in that X1 in chemical formula (3) is O and X2 is represented by chemical formula (11).
  • Examples 13 to 15 also differ in the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polyacrylic acid compound.
  • Examples 16 and 17 differ from Examples 11 and 12 in that the binder used in the negative electrode was changed. Examples 16 and 17 differ from Examples 11 and 12 in that R in the unit structures of chemical formula (1), chemical formula (2), and chemical formula (3) was changed to H, and X2 in chemical formula (3) was changed. In Example 16, X2 in chemical formula (3) was represented by chemical formula (12). In Example 17, X2 in chemical formula (3) was represented by chemical formula (13).
  • Example 18 differs from Example 2 in that the binder used in the negative electrode was changed.
  • the binder of Example 18 differs from Example 2 in the molar ratio of the unit structures and in that X1 in chemical formula (3) is NCH3 and X2 is represented by chemical formula (14).
  • Example 19 differs from Example 2 in that the binder used in the negative electrode was changed.
  • the binder of Example 19 differs from Example 2 in that X1 in the chemical formula (3) is NH and X2 is represented by the chemical formula (15).
  • Example 20 differs from Example 11 in that the binder used in the negative electrode was changed.
  • the binder of Example 20 differs from Example 11 in that X1 in the chemical formula (3) is NH and X2 is represented by the chemical formula (16).
  • Comparative Example 1 differs from Example 1 in that the binder used in the negative electrode was changed.
  • the binder in Comparative Example 1 was a polyacrylic acid compound having a unit structure represented by chemical formula (1).
  • R in the unit structure of chemical formula (1) was H.
  • Comparative Examples 2 and 3 differ from Example 2 in that the binder used in the negative electrode was changed.
  • the binders in Comparative Examples 2 and 3 differ from Example 2 in the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polyacrylic acid compound.
  • the capacity and cycle characteristics per gram of the negative electrode active material layer were measured for Examples 2 to 20 and Comparative Examples 1 to 3 in the same manner as in Example 1.
  • the binder configurations and measurement results for Examples 1 to 20 and Comparative Examples 1 to 3 are shown in Table 1 below.
  • Examples 1 to 20 had a higher capacity retention rate than Comparative Examples 1 to 3. This is believed to be because the binder contained in the negative electrode active material layer 34 penetrates between the active materials and between the active material and the current collector foil, enhancing the binding strength between them.
  • the present invention makes it possible to provide a lithium-ion secondary battery with excellent cycle characteristics.

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Abstract

Le liant pour batterie secondaire au lithium-ion de l'invention possède un composé acide polyacrylique ayant au moins une des formules chimiques prédéfinies (1), (2) et (3) pour structure unitaire. Ce liant pour batterie secondaire au lithium-ion présente un rapport supérieur ou égal à 1,5 et inférieur ou égal à 6,0 entre sa masse moléculaire moyenne en poids et sa masse moléculaire moyenne en nombre mesurées par chromatographie par perméation sur gel.
PCT/JP2024/004066 2023-02-28 2024-02-07 Liant pour batterie secondaire au lithium-ion, électrode négative pour batterie secondaire au lithium-ion, et batterie secondaire au lithium-ion Ceased WO2024181064A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015186363A1 (fr) * 2014-06-04 2015-12-10 日本ゼオン株式会社 Composition de liant pour électrode de batterie rechargeable au lithium-ion, composition de boue pour électrode de batterie rechargeable au lithium-ion, électrode de batterie rechargeable au lithium-ion, et batterie rechargeable au lithium-ion
JP2018160382A (ja) * 2017-03-23 2018-10-11 Tdk株式会社 リチウムイオン二次電池
JP2020532847A (ja) * 2017-12-27 2020-11-12 エルジー・ケム・リミテッド リチウム‐硫黄電池用バインダー、これを含む正極及びリチウム‐硫黄電池
CN113711385A (zh) * 2020-12-28 2021-11-26 宁德新能源科技有限公司 负极极片、电化学装置和电子装置
CN115472834A (zh) * 2021-06-11 2022-12-13 华为技术有限公司 聚合物、包括该聚合物的粘结剂和负极、负极的制备方法

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015186363A1 (fr) * 2014-06-04 2015-12-10 日本ゼオン株式会社 Composition de liant pour électrode de batterie rechargeable au lithium-ion, composition de boue pour électrode de batterie rechargeable au lithium-ion, électrode de batterie rechargeable au lithium-ion, et batterie rechargeable au lithium-ion
JP2018160382A (ja) * 2017-03-23 2018-10-11 Tdk株式会社 リチウムイオン二次電池
JP2020532847A (ja) * 2017-12-27 2020-11-12 エルジー・ケム・リミテッド リチウム‐硫黄電池用バインダー、これを含む正極及びリチウム‐硫黄電池
CN113711385A (zh) * 2020-12-28 2021-11-26 宁德新能源科技有限公司 负极极片、电化学装置和电子装置
CN115472834A (zh) * 2021-06-11 2022-12-13 华为技术有限公司 聚合物、包括该聚合物的粘结剂和负极、负极的制备方法

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