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WO2025183131A1 - Batterie secondaire au lithium - Google Patents

Batterie secondaire au lithium

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Publication number
WO2025183131A1
WO2025183131A1 PCT/JP2025/007020 JP2025007020W WO2025183131A1 WO 2025183131 A1 WO2025183131 A1 WO 2025183131A1 JP 2025007020 W JP2025007020 W JP 2025007020W WO 2025183131 A1 WO2025183131 A1 WO 2025183131A1
Authority
WO
WIPO (PCT)
Prior art keywords
protective layer
secondary battery
lithium secondary
lithium
unit
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/JP2025/007020
Other languages
English (en)
Japanese (ja)
Inventor
智勝 和田
聡 蚊野
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.)
Panasonic Intellectual Property Management Co Ltd
Original Assignee
Panasonic Intellectual Property Management 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 Panasonic Intellectual Property Management Co Ltd filed Critical Panasonic Intellectual Property Management Co Ltd
Publication of WO2025183131A1 publication Critical patent/WO2025183131A1/fr
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
    • 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
    • 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

  • This disclosure relates to lithium secondary batteries.
  • Lithium ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries.
  • Lithium secondary batteries (lithium metal secondary batteries) are promising non-aqueous electrolyte secondary batteries with even higher capacities than lithium ion batteries.
  • lithium metal secondary batteries lithium metal precipitates on the negative electrode during charging, and this lithium metal dissolves in the non-aqueous electrolyte as lithium ions during discharge.
  • Patent Document 1 discloses "a lithium secondary battery comprising: a positive electrode that absorbs lithium ions during discharge and releases the lithium ions during charge; a negative electrode in which lithium metal precipitates during charge and dissolves during discharge; and a non-aqueous electrolyte having lithium ion conductivity, wherein the surface of the negative electrode is covered with a protective layer, and the protective layer includes a block polymer in which a first polymer segment having a repeating structure of monomer unit A and a second polymer segment having a repeating structure of monomer unit B are bonded together.”
  • Patent Document 1 of Patent Document 2 discloses "a negative electrode for a lithium battery comprising lithium metal and a protective layer disposed on at least a portion of the lithium metal, wherein the protective layer comprises a block copolymer comprising a structural domain and a hard domain covalently bonded to the structural domain, the structural domain comprising a structural block of the block copolymer, the hard domain comprising a hard block of the block copolymer, the structural domain comprising a plurality of structural repeat units, and the hard block comprising a plurality of olefin repeat units.”
  • Claim 1 of Patent Document 3 discloses "a negative electrode for a lithium metal battery, comprising: a lithium metal electrode containing lithium metal or a lithium metal alloy; and a protective film disposed on at least a portion of the lithium metal electrode, wherein the protective film has a Young's modulus of 10 6 Pa or more and contains one or more particles selected from organic particles, inorganic particles, and organic-inorganic particles having a size of more than 1 ⁇ m and not more than 100 ⁇ m.”
  • One of the objectives of this disclosure is to provide a lithium secondary battery with a high capacity retention rate.
  • a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte
  • the negative electrode is an electrode on which lithium metal precipitates during charging and from which the lithium metal dissolves during discharging
  • a protective layer is disposed on the surface of the negative electrode, the protective layer comprising a fluorinated polymer and a block copolymer, the block copolymer comprising a first polymer portion having a repeating structure of monomer unit A and a second polymer portion having a repeating structure of monomer unit B, and the fluorinated polymer and the block copolymer being present in the protective layer as separate molecules.
  • FIG. 1 is a cross-sectional view schematically illustrating an example of a lithium secondary battery according to a first embodiment.
  • 1 is a cross-sectional view schematically illustrating a portion of an example of an electrode group used in a lithium secondary battery according to a first embodiment.
  • FIG. 3 is a cross-sectional view schematically illustrating a portion of another example of an electrode group used in the lithium secondary battery of Embodiment 1.
  • the lithium secondary battery according to this embodiment may be referred to as a "lithium secondary battery (B)" hereinafter.
  • the lithium secondary battery (B) includes a positive electrode, a negative electrode, and a non-aqueous electrolyte.
  • the negative electrode is an electrode on which lithium metal precipitates during charging and from which lithium metal dissolves during discharging.
  • a protective layer is disposed on the surface of the negative electrode.
  • the protective layer includes a fluorinated polymer and a block copolymer.
  • the block copolymer includes a first polymer portion having a repeating structure of monomer unit A and a second polymer portion having a repeating structure of monomer unit B.
  • the fluorinated polymer and the block copolymer exist as separate molecules in the protective layer. In other words, the fluorinated polymer and the block copolymer exist as independent molecules in the protective layer.
  • a protective layer By forming a protective layer on the surface of the negative electrode, it is possible to prevent lithium metal from precipitating in a dendritic form. Therefore, by forming the protective layer, it is possible to prevent the expansion of the electrode group during charging. Furthermore, by forming the protective layer, contact between the lithium metal and the non-aqueous electrolyte is prevented, and as a result, side reactions between the lithium metal and the non-aqueous electrolyte are suppressed. By preventing the dendritic precipitation of lithium metal and the side reactions between the lithium metal and the non-aqueous electrolyte, the capacity retention rate is increased.
  • monomer unit A (or B) refers to a unit formed in a polymer by polymerized monomer A (or B).
  • a block copolymer in the protective layer it is possible to achieve both the functions of the first polymer portion and the second polymer portion. Compared to when a protective layer is formed from a mixture of a homopolymer corresponding to the first polymer portion and a homopolymer corresponding to the second polymer portion, when a block copolymer is used, the disadvantages of the first polymer portion and the second polymer portion cancel each other out. Therefore, by using a block copolymer, it is possible to achieve high effectiveness.
  • the polymer forming the protective layer have high lithium ion conductivity.
  • polymers with high lithium ion conductivity have a high affinity for the electrolyte and may be easily dissolved in the electrolyte.
  • using a polymer with high lithium ion conductivity can easily reduce the strength of the protective layer. If the protective layer's strength is low, lithium metal dendrites may penetrate the protective layer, or the protective layer may break as the negative electrode expands and contracts during charge and discharge. As a result, the discharge capacity decreases as the number of charge and discharge cycles increases.
  • a block copolymer containing a first polymer portion with high mechanical strength and a second polymer portion with high lithium ion conductivity may be used. Using such a block copolymer makes it possible to achieve both high mechanical strength and high lithium ion conductivity.
  • Block copolymers can aggregate with each other to form a secondary structure.
  • the secondary structure can be formed so that portions of the block copolymer having the same monomer units are positioned in close proximity. That is, the secondary structure of the block copolymer can be formed so that the first polymer portions of multiple block copolymers aggregate and the second polymer portions of multiple block copolymers aggregate.
  • the secondary structure of an ABA triblock copolymer can be easily controlled by controlling the types of monomer units in the first and second polymer portions and the degree of polymerization (number average molecular weight) of the first and second polymer portions.
  • the ratio Mf/Ms of the mass of the fluoropolymer Mf to the sum Ms of the mass of the fluoropolymer and the mass of the block copolymer may be 0.20 or more, or 0.50 or more, or 0.95 or less, or 0.80 or less.
  • the strength of the protective layer against shear can be particularly increased. As a result, a decrease in capacity retention due to breakage of the protective layer can be particularly suppressed.
  • the total proportion of the fluorinated polymer and block copolymer in the protective layer may be 50% by mass or more, 80% by mass or more, or 90% by mass or more, or may be 100% by mass or less, 90% by mass or less, or 80% by mass or less.
  • the negative electrode may include a layer containing LiF (lithium fluoride) on the surface in contact with the protective layer.
  • LiF lithium fluoride
  • This configuration suppresses side reactions between the negative electrode and the non-aqueous electrolyte, improving capacity retention.
  • a protective layer containing a fluorinated polymer it is possible to form a LiF layer.
  • the protective layer includes a fluoropolymer.
  • a fluoropolymer is a polymer containing fluorine.
  • the fluoropolymer may be a polymer that is not a block copolymer.
  • Examples of the non-block copolymer include homopolymers and random copolymers.
  • Examples of the fluoropolymer include polyvinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride and hexafluoropropylene, and copolymers of vinylidene fluoride and trifluoroethylene.
  • the number average molecular weight of the fluoropolymer may be 500,000 or more, or 800,000 or more, or may be 1,500,000 or less, or 1,000,000 or less.
  • the fluoropolymer may be a commercially available fluoropolymer. Alternatively, the fluoropolymer may be synthesized using a known synthesis method.
  • the protective layer includes a block copolymer.
  • the block copolymer may be a fluorine-free polymer.
  • the fluorinated polymer and the block copolymer are easily separated within the protective layer.
  • the block copolymer is easily disposed on the surface side of the protective layer, and the fluorinated polymer is easily disposed on the negative electrode side of the protective layer. This configuration makes it easier to obtain the effect of improving mechanical strength by the block copolymer and the effect of forming a LiF layer by the fluorinated polymer.
  • the form of the block copolymer is not limited, and may be AB type or ABA type.
  • the block copolymer may be an ABA type triblock copolymer in which a first polymer portion (e.g., a linear first polymer portion) is bonded to both ends of a second polymer portion (e.g., a linear second polymer portion).
  • a commercially available block copolymer may be used as the block copolymer.
  • the block copolymer may be synthesized using a known synthesis method.
  • the first polymer portion of the block copolymer may be a polymer with high mechanical strength (e.g., tensile strength).
  • the tensile strength of the first polymer portion may be higher than the tensile strength of the second polymer portion.
  • the swelling degree of the second polymer portion in the non-aqueous electrolyte may be higher than the swelling degree of the first polymer portion in the non-aqueous electrolyte.
  • a protective layer with high lithium ion conductivity can be formed. The higher the swelling degree, the more likely it is that the strength of the protective layer will decrease, but by using a block copolymer containing the first polymer portion and the second polymer portion, the strength of the protective layer can be maintained.
  • a second polymer portion made of a polymer that dissolves in the non-aqueous electrolyte alone it can be used in the protective layer by combining the first polymer portion and the second polymer portion.
  • the tensile strength and swelling degree of the first and second polymer portions can be determined by the following method. First, the lithium secondary battery is disassembled and the protective layer is removed. Next, the structure of the block copolymer contained in the protective layer is analyzed. By analyzing the structure of the block copolymer, the structures of the first polymer portion and the second polymer portion contained in the block copolymer can be identified. Specifically, the types of monomer units A and B (or the types of monomers A and B) and the molecular weight of the polymer portions can be identified. Next, if necessary, a first polymer that is a homopolymer of the identified monomer A and a second polymer that is a homopolymer of the identified monomer B are synthesized. Then, the tensile strength and swelling degree (swelling degree in a non-aqueous electrolyte) of these polymers are measured. In this way, the tensile strength and swelling degree of the first and second polymer portions can be determined.
  • the tensile strength is listed in a publicly available database, that value can be used. If the tensile strength is not listed in a publicly available database, the tensile strength can be determined in accordance with JIS (Japanese Industrial Standards) K 7161 by forming a sample of a specified shape.
  • JIS Japanese Industrial Standards
  • the degree of swelling of a polymer can be determined by the following method. First, the lithium secondary battery is disassembled to remove the non-aqueous electrolyte. Next, the components of the non-aqueous electrolyte are analyzed. Next, a non-aqueous electrolyte with the same components as those obtained by analysis is prepared, and the polymers (first polymer and second polymer) are immersed in the non-aqueous electrolyte in an environment of 40°C. Then, the mass of the polymer before immersion in the non-aqueous electrolyte and the mass of the polymer after immersion in the non-aqueous electrolyte are measured. The rate of increase in the mass of the polymer due to immersion in the non-aqueous electrolyte is taken as the degree of swelling of the polymer.
  • Whether a polymer is a copolymer can be determined by end group quantitation using GPC (gel permeation chromatography)-NMR. If the polymer is a block copolymer, its structure (for example, whether it is a triblock copolymer or a random copolymer) can also be determined by end group quantitation using GPC (gel permeation chromatography)-NMR.
  • GPC gel permeation chromatography
  • Monomer unit A may have a hydrocarbon skeleton.
  • Monomer unit A may be any one of a styrene unit, an ethylene unit, a butylene unit, and a propylene unit.
  • the first polymer portion may be any one of polystyrene, polyethylene, polybutylene, and polypropylene.
  • Polystyrene is preferable because it is stable against non-aqueous electrolytes, has sufficient mechanical strength, and is inexpensive. That is, a preferred example of monomer A is styrene.
  • 90 mol % or more (e.g., 95 mol % or more) of the monomer units constituting the first polymer portion may be monomer unit A. That is, 10 mol % or less (e.g., 5 mol % or less) of the monomer units constituting the first polymer portion may be a monomer unit other than monomer unit A (e.g., monomer unit B).
  • Monomer unit B may contain oxygen.
  • Monomer unit B may be any one of a methyl methacrylate unit, an ethyl methacrylate unit, a propyl methacrylate unit, an ethylene glycol unit, a propylene glycol unit, a butylene glycol unit, and a methacrylic acid unit.
  • Monomer B may be a monomer that becomes any of these units.
  • the second polymer portion may be a polymer obtained by homopolymerizing monomer B.
  • Monomer B is preferably methyl methacrylate. That is, the second polymer portion is preferably polymethyl methacrylate (PMMA).
  • 90 mol % or more (e.g., 95 mol % or more) of the monomer units constituting the second polymer portion may be monomer unit B. That is, 10 mol % or less (e.g., 5 mol % or less) of the monomer units constituting the second polymer portion may be a monomer unit other than monomer unit B (e.g., monomer unit A).
  • the block copolymer may satisfy the following conditions (1) and/or (2): (1)
  • the monomer unit A is any one of a styrene unit, an ethylene unit, a butylene unit, and a propylene unit.
  • the monomer unit B is any one of a methyl methacrylate unit, an ethyl methacrylate unit, a propyl methacrylate unit, an ethylene glycol unit, a propylene glycol unit, a butylene glycol unit, and a methacrylic acid unit.
  • the block copolymer may satisfy the following condition (1a) and/or (2a): Furthermore, the block copolymer may satisfy the following condition (1c): (1a) Monomer unit A is a styrene unit. (2a) Monomer unit B is a methyl methacrylate unit. (1c) The block copolymer is an ABA type triblock copolymer in which a second polymer segment is attached to both ends of a first polymer segment.
  • the number average molecular weight of the first polymer portion may be smaller than the number average molecular weight of the second polymer portion. This configuration makes it easier to prepare the coating liquid for forming the protective layer.
  • the block copolymer may satisfy at least one of the following conditions (3) to (5): For example, the block copolymer may satisfy condition (3) and further satisfy conditions (4) and/or (5).
  • (3) The number average molecular weight of the first polymer portion is less than the number average molecular weight of the second polymer portion.
  • (4) The number average molecular weight of the first polymer portion is 1,000 or more and 100,000 or less.
  • (5) The number average molecular weight of the second polymer portion is 10,000 or more and 500,000 or less.
  • the number average molecular weight of the first polymer portion may be 1,000 or more, or 10,000 or more, and may be 100,000 or less, or 50,000 or less.
  • the number average molecular weight of the second polymer portion may be 10,000 or more, or 100,000 or more, and may be 500,000 or less, or 200,000 or less.
  • the average thickness of the protective layer may be 0.1 ⁇ m or more and 5 ⁇ m or less, or 0.5 ⁇ m or more and 2 ⁇ m or less.
  • the average thickness of the protective layer can be measured by the following procedure. First, a cross-sectional image of the protective layer is obtained using a scanning electron microscope (SEM). Next, the thickness of any 10 points on the protective layer is measured using the cross-sectional image. The average thickness of the protective layer is determined by arithmetically averaging the thicknesses measured at the 10 points.
  • the protective layer may contain a lithium salt.
  • the protective layer contains a lithium salt, the charge-discharge reaction proceeds more easily when the battery is first used.
  • the lithium salt is preferably contained in the protective layer when the protective layer is formed.
  • the protective layer is preferably formed using a material containing the above-mentioned polymer and lithium salt.
  • the lithium salt may include at least one selected from the group consisting of LiBF 4 , LiPF 6 , LiClO 4 , LiCF 3 SO 3 , LiC(CF 3 SO 2 ) 3 , LiN(SO 2 C 2 F 5 ) 2 , LiN(SO 2 CF 3 ) 2 , Li (SO 2 F) 2 , LiPF 3 (CF 2 CF 3 ) 3 , and LiPF 3 (CF 3 ) 3 , or may be any one selected from the group.
  • the protective layer may contain materials other than fluorinated polymers and block copolymers.
  • materials include resins other than fluorinated polymers and block copolymers, and inorganic particles.
  • resins include polyolefin resins, silicone resins, and epoxy resins.
  • the inorganic particles are particles made of an inorganic material (e.g., metal oxide, metal hydroxide, metal composite oxide, metal nitride, metal carbide, metal fluoride, etc.).
  • the mixture of the polymer and inorganic particles in the protective layer tends to increase the lithium ion conductivity of the protective layer. As a result, lithium ions move smoothly between the negative electrode and the non-aqueous electrolyte through the protective layer during charge and discharge.
  • the density of the inorganic particles may be 6 g/ cm3 or more.
  • the density of the inorganic particles may be 3.5 times or more the density of the areas of the protective layer occupied by materials other than the inorganic particles.
  • the inorganic particles tend to be deposited thinly and densely when forming the protective layer.
  • uneven distribution of the inorganic particles due to aggregation is suppressed, and the thickness and strength of the protective layer tend to be uniform.
  • Examples of inorganic materials constituting the inorganic particles include copper oxide, bismuth oxide, tungsten oxide, indium oxide, and silver oxide.
  • the inorganic particles may include at least one selected from the group consisting of copper oxide particles and bismuth oxide particles. In this case, it is easy to make the density of the inorganic particles 6 g/cm3 or more . Furthermore, in this case, it is easy to make the density of the inorganic particles 3.5 times or more the density of the region of the protective layer occupied by materials other than the inorganic particles.
  • the proportion of the block copolymer in the total of the fluoropolymer, block copolymer, and resin material may be 80% or more (e.g., 90% or more, or 95% or more) by mass.
  • the proportion of inorganic particles in the protective layer may be 50% by mass or less, 35% by mass or less, or 20% by mass or more. The proportion may also be 5% by mass or more and 20% by mass or less. When the proportion of inorganic particles in the protective layer is within the above range, the flexibility, strength, and lithium ion conductivity of the protective layer are sufficiently ensured.
  • the method for forming the protective layer is not particularly limited.
  • the protective layer may be formed by the following method.
  • a coating liquid for forming the protective layer is prepared.
  • the coating liquid can be prepared by mixing a fluorinated polymer, a block copolymer, a liquid component, and, as necessary, other materials (lithium salt, resin, inorganic particles, etc.).
  • the liquid component is not particularly limited, and N-methyl-2-pyrrolidone, dimethyl ether, tetrahydrofuran, etc. may be used.
  • the coating liquid is applied to the negative electrode current collector (or negative electrode substrate) and then dried.
  • the application and drying methods are not particularly limited, and known methods may be used. For example, application may be performed using a bar coater, applicator, gravure coater, etc. In this manner, the protective layer is formed.
  • the fluoropolymer and block copolymer may be present in the protective layer in the form of particles. However, if the fluoropolymer and block copolymer are present in the protective layer in the form of particles, their respective properties will not be fully exhibited. Therefore, it is preferable that the fluoropolymer and block copolymer are not present in the protective layer in the form of particles. In other words, it is preferable that the fluoropolymer and block copolymer are present in the protective layer in a non-particulate state. Therefore, it is preferable to form the protective layer using a coating liquid containing the fluoropolymer and block copolymer in a non-particulate state.
  • a space be formed between the negative electrode and positive electrode in which lithium metal can be deposited.
  • This space can be formed by placing a spacer between the negative electrode and positive electrode.
  • the spacer may be made of the same material as the protective layer.
  • the thickness of the protective layer may be increased in parts, and the thicker parts may be used as spacers.
  • the spacers may be integrated with the protective layer.
  • a spacer-forming coating liquid may be applied linearly onto the protective layer to form linear convex portions (spacers).
  • the coating liquid for forming the protective layer may be used as the spacer-forming coating liquid.
  • the spacer may be formed on the positive electrode, the protective layer, or the separator.
  • the spacer may be disposed between the positive electrode and the separator, or between the protective layer and the separator.
  • the spacer may be composed of linear convex portions and/or dot-shaped convex portions.
  • the linear convex portions may be arranged in a striped pattern or in a mesh pattern (e.g., a honeycomb pattern).
  • the height of the spacer may be 10 ⁇ m or more and 100 ⁇ m or less.
  • the width of the spacer may be 200 ⁇ m or more and 2000 ⁇ m or less.
  • the method for manufacturing the lithium secondary battery (B) is not particularly limited.
  • the lithium secondary battery (B) may be formed by combining the method described in this specification with a known method.
  • Examples of the components of the lithium secondary battery (B) will be specifically described below. Note that the components described below are merely examples, and the components of the lithium secondary battery (B) of this embodiment are not limited to the following examples. Known components may be used for components other than those characteristic of this embodiment.
  • the lithium secondary battery (B) may include an electrode group composed of a positive electrode, a negative electrode, and a separator.
  • the electrode group may be of a wound type or a laminated type.
  • a wound electrode group is formed by winding a positive electrode, a negative electrode, and a separator.
  • the negative electrode includes a negative electrode current collector.
  • lithium metal is deposited on the surface of the negative electrode upon charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode upon charging, becoming lithium metal and depositing on the surface of the negative electrode. The deposited lithium metal dissolves as lithium ions in the non-aqueous electrolyte upon discharging.
  • the lithium ions contained in the non-aqueous electrolyte may be derived from a lithium salt added to the non-aqueous electrolyte or may be supplied from the positive electrode active material.
  • a protective layer covers the surface of the negative electrode current collector.
  • a protective layer covers the surface of the lithium metal.
  • a conductive sheet can be used for the negative electrode current collector.
  • the conductive sheet may be a metal foil.
  • the material of the negative electrode current collector (conductive sheet) may be a conductive material other than lithium metal or a lithium alloy.
  • the conductive material may be a metal material.
  • the conductive material may be a material that does not react with lithium.
  • the conductive material may be a material that does not form an alloy with lithium or an intermetallic compound with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), alloys containing these metal elements, and graphite with its basal surface preferentially exposed. Examples of alloys include copper alloys and stainless steel (SUS). Copper and copper alloys are preferred materials for the negative electrode current collector because of their high conductivity.
  • the negative electrode current collector may be copper foil, copper alloy foil, or stainless steel foil.
  • the thickness of the negative electrode current collector is not particularly limited and may be 5 ⁇ m or more and 300 ⁇ m or less.
  • the negative electrode may include a negative electrode current collector and lithium-containing metal layers laminated on both sides of the negative electrode current collector.
  • a protective layer can be formed on the lithium-containing metal layer.
  • the lithium-containing metal layer laminated on the negative electrode current collector is a lithium metal layer or a lithium alloy layer.
  • the lithium alloy layer contains trace amounts of elements other than lithium (10 atomic % or less). Examples of elements other than lithium contained in lithium alloys include aluminum, magnesium, indium, and zinc.
  • Forming a lithium-containing metal layer can suppress the decrease in discharge capacity due to repeated charge and discharge. Furthermore, forming a lithium-containing metal layer can suppress the dendritic deposition of lithium metal.
  • the method for forming the lithium-containing metal layer is not particularly limited, and it can be formed by known methods.
  • the lithium-containing metal layer can be formed by pressing a lithium metal foil or a lithium alloy foil onto the negative electrode current collector.
  • the lithium-containing metal layer is dense, which distinguishes it from the lithium metal (generally porous) that precipit
  • the positive electrode includes a positive electrode mixture layer containing a positive electrode active material.
  • the positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector.
  • the positive electrode mixture layer may include a positive electrode active material and additives (such as a conductive material, a binder, or a thickener).
  • the positive electrode mixture layer may be formed on only one side of the positive electrode current collector, or on both sides of the positive electrode current collector.
  • the positive electrode can be formed using known methods. For example, first, a positive electrode mixture slurry containing a positive electrode active material and additives is prepared. Next, the positive electrode mixture slurry is applied to a positive electrode current collector and then dried to form a coating. Next, the laminate consisting of the positive electrode current collector and coating is rolled to obtain a positive electrode. The formed positive electrode is then cut to a specified size as necessary.
  • the positive electrode active material can be a material capable of reversibly absorbing and releasing lithium ions.
  • positive electrode active materials include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Lithium-containing transition metal oxides are preferred because of their low manufacturing costs and high average discharge voltage.
  • transition metal elements contained in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W.
  • the lithium-containing transition metal oxides may contain only one type of transition metal element, or may contain two or more types.
  • the transition metal element may be at least one selected from the group consisting of Co, Ni, and Mn.
  • the lithium-containing transition metal oxides may contain one or more typical elements. Examples of typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, Bi, and B.
  • Carbon materials can be used as the conductive material.
  • Examples of carbon materials include carbon black (acetylene black, ketjen black, etc.), carbon nanotubes, and graphite.
  • binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, rubber-like polymers, etc.
  • fluororesins include polytetrafluoroethylene and polyvinylidene fluoride, etc.
  • Cellulose derivatives and the like can be used as thickeners.
  • cellulose derivatives include carboxymethyl cellulose (CMC) and its modified forms, methyl cellulose, etc.
  • modified CMC include salts of CMC.
  • salts include alkali metal salts (e.g., sodium salts) and ammonium salts.
  • a conductive sheet can be used for the positive electrode current collector.
  • Examples of conductive sheets include metal foil.
  • the surface of the positive electrode current collector may be coated with a carbon material.
  • Examples of materials for the positive electrode current collector include metal materials containing Al, Ti, Fe, etc.
  • the metal material may also be Al, Al alloy, Ti, Ti alloy, Fe alloy (e.g., stainless steel), etc.
  • the thickness of the positive electrode current collector is not particularly limited and may be in the range of 5 to 300 ⁇ m.
  • the separator is made of a porous sheet having ion permeability and insulating properties.
  • the porous sheet include a microporous membrane, a woven fabric, and a nonwoven fabric.
  • the material of the separator is not particularly limited and may be a polymer material.
  • the polymer material include an olefin resin, a polyamide resin, and cellulose.
  • the olefin resin include polyethylene, polypropylene, and a copolymer of ethylene and propylene.
  • the separator may contain additives (such as an inorganic filler) as needed.
  • the thickness of the separator is not particularly limited and may be 5 ⁇ m or more and 20 ⁇ m or less (e.g., 10 ⁇ m or more and 20 ⁇ m or less).
  • the non-aqueous electrolyte may be a non-aqueous electrolyte having lithium ion conductivity.
  • the non-aqueous electrolyte may be liquid or gel-like.
  • a liquid non-aqueous electrolyte can be prepared by dissolving a lithium salt in a non-aqueous solvent. When the lithium salt dissolves in the non-aqueous solvent, lithium ions and anions are generated.
  • the gel-like non-aqueous electrolyte may contain a lithium salt and a matrix polymer, or may contain a lithium salt, a non-aqueous solvent, and a matrix polymer.
  • the matrix polymer may be a polymer material that absorbs the non-aqueous solvent and gels. Examples of polymer materials include fluororesin, acrylic resin, and polyether resin.
  • non-aqueous solvents can be used as the non-aqueous solvent.
  • non-aqueous solvents that can be used include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, chain ethers, fluorinated chain ethers, cyclic ethers, and fluorinated cyclic ethers.
  • cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC).
  • chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).
  • cyclic carboxylic acid esters examples include gamma-butyrolactone (GBL) and gamma-valerolactone (GVL).
  • chain carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.
  • cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran.
  • chain ethers examples include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.
  • One type of nonaqueous solvent may be used alone, or two or more types may be used in combination.
  • lithium salts of chlorine-containing acids LiClO4 , LiAlCl4 , LiB10Cl10 , etc.
  • lithium salts of fluorine-containing acids LiPF6 , LiPF2O2 , LiBF4 , LiSbF6, LiAsF6 , LiCF3SO3 , LiCF3CO2 , etc.
  • lithium salts of fluorine-containing acid imides LiN(FSO2) 2 , LiN(CF3SO2 )2 , LiN( CF3SO2 ) ( FSO2 ), LiN( CF3SO2 ) ( C4F9SO2 ) , LiN ( C2F5SO2 ) ) .
  • lithium salts may be used alone or in combination of two or more.
  • the concentration of the lithium salt in the non-aqueous electrolyte may be 0.5 mol/L or more, 1.0 mol/L or more, or 1.5 mol/L or more, and may be 3.5 mol/L or less, 2.0 mol/L or less, or 1.5 mol/L or less.
  • the non-aqueous electrolyte may contain additives (e.g., known additives).
  • additives include 1,3-propane sultone, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, and fluorobenzene.
  • the exterior housing accommodates the nonaqueous electrolyte and the electrode group.
  • the exterior housing is not particularly limited, and known exterior housings can be used.
  • the shape of the exterior housing is selected according to the shape of the lithium secondary battery (B).
  • the shape of the lithium secondary battery (B) is not limited, and may be cylindrical, prismatic, or any other shape.
  • the exterior housing may include a cylindrical battery case with a bottom, and a sealing body and a gasket that seal the opening of the battery case.
  • lithium secondary battery (B) of this embodiment will be described in detail with reference to the drawings.
  • the components described above can be applied to the components of the example lithium secondary battery described below.
  • the components of the example described below can be modified based on the above description.
  • the matters described below may be applied to the above embodiment.
  • components that are not essential for the lithium secondary battery (B) according to the present disclosure may be omitted.
  • FIG. 1 is a longitudinal cross-sectional view schematically illustrating an example of a lithium secondary battery according to Embodiment 1.
  • the cylindrical lithium secondary battery 10 shown in FIG. 1 includes a cylindrical battery case and an electrode group 14 and a nonaqueous electrolyte (not shown) housed in the battery case.
  • the electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator 13.
  • the electrode group 14 is a wound electrode group formed by winding the positive electrode 11, the negative electrode 12, and the separator 13.
  • the separator 13 is disposed between the positive electrode 11 and the negative electrode 12.
  • the positive electrode 11 is electrically connected to a cap 26, which also serves as a positive electrode terminal, via a positive electrode lead 19.
  • the negative electrode 12 is electrically connected to a case body 15, which also serves as a negative electrode terminal, via a negative electrode lead 20.
  • the battery case includes a case body 15, which is a cylindrical metal container with a bottom, and a sealing body 16 that seals the opening of the case body 15.
  • a gasket 27 is disposed between the case body 15 and the sealing body 16. The gasket 27 ensures the airtightness of the battery case.
  • insulating plates 17 and 18 are disposed at both ends of the electrode group 14 in the winding axis direction.
  • the case body 15 has a step portion 21.
  • the sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26.
  • the lower valve body 23 and the upper valve body 25 are connected at their respective centers.
  • An insulating member 24 is disposed between the peripheral edge of the lower valve body 23 and the peripheral edge of the upper valve body 25.
  • the filter 22 and the lower valve body 23 are connected at their respective peripheral edges.
  • the upper valve body 25 and the cap 26 are connected at their respective peripheral edges. All of the components constituting the sealing body 16, except for the insulating member 24, are electrically connected.
  • the lower valve body 23 has a vent hole. Therefore, if the internal pressure of the battery case increases due to abnormal heat generation or the like, the upper valve body 25 bulges toward the cap 26 and separates from the lower valve body 23. This cuts off the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure increases further, the upper valve body 25 breaks, and gas is released from the opening formed in the cap 26.
  • FIG. 2 shows an example in which lithium metal is not deposited on the surface of the negative electrode current collector.
  • the negative electrode 12 includes a negative electrode current collector 32.
  • the surface of the negative electrode current collector 32 is covered with a protective layer 40.
  • the protective layer 40 includes a fluorinated polymer and a block copolymer.
  • FIG. 3 shows an example of a state in which lithium metal is not deposited on the surface of the negative electrode current collector.
  • the example electrode group 14 shown in Figure 3 differs from the electrode group 14 shown in Figure 2 in that it includes a spacer 50. Duplicate explanations of matters explained in Figure 2 may be omitted.
  • the surface of the negative electrode current collector 32 (negative electrode 12) is covered with a protective layer 40.
  • the protective layer 40 contains a fluorinated polymer and a block copolymer.
  • a spacer 50 is disposed between the protective layer 40 and the separator 13.
  • the spacer 50 is composed of linear protrusions arranged along the longitudinal direction of the separator 13.
  • a space 51 is formed between the negative electrode 12 and the separator 13 by the spacer 50.
  • the lithium metal that deposits on the negative electrode current collector 32 during charging is pressed by the separator 13 and accommodated in the space 51 between the negative electrode 12 and the separator 13.
  • the lithium metal is accommodated in the space 51 between the negative electrode 12 and the separator 13, the apparent volume change of the electrode group due to the deposition of lithium metal during charge/discharge cycles is reduced. This also reduces the stress applied to the negative electrode current collector 32. Furthermore, pressure is applied from the separator 13 to the lithium metal accommodated between the negative electrode 12 and the separator 13. As a result, the deposited lithium metal is less likely to become isolated, and a decrease in charge/discharge efficiency is suppressed.
  • a lithium secondary battery A positive electrode and a negative electrode; a non-aqueous electrolyte; the negative electrode is an electrode in which lithium metal is deposited during charging and in which the lithium metal dissolves during discharging, a protective layer is disposed on the surface of the negative electrode; the protective layer comprises a fluorinated polymer and a block copolymer; the block copolymer comprises a first polymer portion having repeating units of monomer unit A and a second polymer portion having repeating units of monomer unit B; The lithium secondary battery, wherein the fluorinated polymer and the block copolymer are present in the protective layer as separate molecules.
  • Technology 2 2.
  • a ratio Mf/Ms of a mass of the fluorinated polymer Mf to a total mass Ms of the fluorinated polymer and the block copolymer is in the range of 0.20 to 0.95.
  • the negative electrode includes a layer containing LiF on a surface in contact with the protective layer.
  • the fluorinated polymer is polyvinylidene fluoride.
  • the block copolymer is an ABA triblock copolymer in which the first polymer portion is bonded to both ends of the second polymer portion.
  • the monomer unit A is any one of a styrene unit, an ethylene unit, a butylene unit, and a propylene unit;
  • the monomer unit B is any one of a methyl methacrylate unit, an ethyl methacrylate unit, a propyl methacrylate unit, an ethylene glycol unit, a propylene glycol unit, a butylene glycol unit, and a methacrylic acid unit.
  • the lithium secondary battery according to the present disclosure will be described in more detail below based on examples. However, the present disclosure is not limited to the following examples. In these examples, several lithium secondary batteries with different protective layers were fabricated and evaluated.
  • the positive electrode active material was a layered rock salt lithium-containing transition metal oxide containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al was 1.0).
  • a positive electrode was formed, comprising a positive electrode current collector and positive electrode mixture layers formed on both sides of the positive electrode current collector.
  • the ratio Mf/Ms of the mass of the fluorinated polymer (Mf) to the total mass Ms of the fluorinated polymer and the block copolymer was set to the value shown in Table 1.
  • the amount of lithium salt added was 1/10 of the sum of Mf and Ms.
  • the block copolymer used was an ABA triblock copolymer (PS-PMMA-PS) in which the first polymer moiety, polystyrene (PS, number-average molecular weight: 9,000), was bonded to both ends of the second polymer moiety, polymethyl methacrylate (PMMA, number-average molecular weight: 19,000).
  • the lithium salt used was lithium bis(fluorosulfonyl)imide.
  • the coating solution was applied to both sides of the negative electrode and dried to form a protective layer (thickness: 2 ⁇ m).
  • a non-aqueous electrolyte was prepared by dissolving LiPF6 and LiBF2 ( C2O4 ) in the non-aqueous solvent so that the concentration of LiPF6 was 1 mol/L and the concentration of LiBF2 ( C2O4 ) was 0.1 mol/L.
  • the electrode group was housed in a bag-shaped exterior body. At this time, the ends of the positive electrode lead and the negative electrode lead were exposed to the outside of the exterior body. After non-aqueous electrolyte was injected into the exterior body, the opening of the exterior body was sealed. In this way, Battery A1 (lithium secondary battery) was produced.
  • the battery was charged at a constant current of 10 mA per unit area (cm 2 ) of the electrode until the battery voltage reached 4.3 V, and then charged at a constant voltage of 4.3 V until the current value per unit area of the electrode reached 1 mA.
  • the battery was discharged at a constant current of 10 mA per unit area (cm 2 ) of the electrode until the battery voltage reached 3 V.
  • Capacity maintenance rate (%) (C2/C1) x 100
  • Batteries A2, A3, C2, and C3 were fabricated in the same manner and under the same conditions as those for fabricating Battery A1, except that when forming the protective layer, the ratio Mf/Ms of the mass of the fluoropolymer Mf to the total mass Ms of the fluoropolymer and the block copolymer was changed as shown in Table 1. No block copolymer was added to the protective layer of Battery C2. No fluoropolymer was added to the protective layer of Battery C3.
  • Battery C1 was fabricated in the same manner and under the same conditions as those for Battery A1, except that no protective layer was formed.
  • the capacity retention rate of the fabricated batteries A2-A3 and C1-C3 was measured in the same manner as for battery A1. Some of the manufacturing conditions and evaluation results are shown in Table 1.
  • Mf/Ms indicates the ratio of the mass of the fluoropolymer (Mf) to the total mass of the fluoropolymer and the block copolymer (Ms). A high capacity retention rate is preferable.
  • Batteries A1 to A3 are lithium secondary batteries (B) according to the present disclosure. Batteries C1 to C3 are comparative examples. As shown in Table 1, Batteries A1 to A3 had significantly higher capacity retention rates than Batteries C1 to C3. While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.
  • This disclosure can be used in lithium secondary batteries.

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  • Chemical Kinetics & Catalysis (AREA)
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Abstract

La batterie secondaire au lithium de l'invention contient une électrode positive (11), une électrode négative (12) et un électrolyte non-aqueux. L'électrode négative (12) est telle qu'un lithium métallique est précipité lors de la charge, et est dissous lors de la décharge. Une couche protectrice (40) est disposée à la surface de l'électrode négative (12). Cette couche protectrice (40) contient un polymère fluoré et un copolymère séquencé. Le copolymère séquencé contient une première portion polymère ayant une structure de répétition d'une unité monomère (A), et une seconde portion polymère ayant une structure de répétition d'une unité monomère (B). Le polymère fluoré et le copolymère séquencé sont présents dans la couche protectrice (40) en tant que molécules séparées.
PCT/JP2025/007020 2024-02-29 2025-02-27 Batterie secondaire au lithium Pending WO2025183131A1 (fr)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005129535A (ja) * 2003-10-23 2005-05-19 Samsung Sdi Co Ltd リチウムポリマー二次電池
JP2005142156A (ja) * 2003-10-31 2005-06-02 Samsung Sdi Co Ltd リチウム金属二次電池用負極及びその製造方法並びにそれを含むリチウム金属二次電池

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005129535A (ja) * 2003-10-23 2005-05-19 Samsung Sdi Co Ltd リチウムポリマー二次電池
JP2005142156A (ja) * 2003-10-31 2005-06-02 Samsung Sdi Co Ltd リチウム金属二次電池用負極及びその製造方法並びにそれを含むリチウム金属二次電池

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