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EP-3825337-B1 - COPOLYMER FOR BINDER FOR NON-AQUEOUS BATTERY ELECTRODE, AND SLURRY FOR PRODUCING NON-AQUEOUS BATTERY ELECTRODE

EP3825337B1EP 3825337 B1EP3825337 B1EP 3825337B1EP-3825337-B1

Inventors

  • KURATA, TOMONORI
  • MARUTA, Shuhei
  • KUNANURUKSAPONG, KIRIDA
  • HANASAKI, MITSURU

Dates

Publication Date
20260506
Application Date
20190712

Claims (13)

  1. A copolymer for a binder for a non-aqueous battery electrode, which is a copolymer (P) of a monomer mixture (M) comprising: a monomer (A) represented by general formula (1); a (meth)acrylic acid monomer (B); and a monomer (C) represented by general formula (2), wherein the content of a structure derived from the monomer (A) in the copolymer (P) is 0.5 to 20.0 mass% and the content of a structure derived from the monomer (C) in the copolymer (P) is 0.5 to 5.0 mass%, wherein R 1 and R 2 each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, wherein R 3 , R 4 , R 5 , and R 6 each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and n is an integer of 1 or more, m is an integer of 0 or more, and (n + m) ≥ 40.
  2. The copolymer for a binder for a non-aqueous battery electrode according to claim 1, wherein in the general formula (2), (n + m) ≦ 500.
  3. The copolymer for a binder for a non-aqueous battery electrode according to claim 1 or claim 2, wherein the monomer mixture (M) further comprises an ethylenically unsaturated monomer (D) having a polar functional group, and the polar functional group is at least one selected the group consisting of a carboxy group, a hydroxy group, an amide group, and a cyano group.
  4. The copolymer for a binder for a non-aqueous battery electrode according to any one of claims 1 to 34, wherein the monomer (A) is N-vinylformamide or N-vinylacetamide.
  5. The copolymer for a binder for a non-aqueous battery electrode according to any one of claims 1 to 4, wherein the weight-average molecular weight is in the range of 1,000,000 to 10,000,000, and the weight-average molecular weight is a pullulan-converted value calculated using gel permeation chromatography (GPC).
  6. The copolymer for a binder for a non-aqueous battery electrode according to any one of claims 3 to 5, wherein the content of a structure derived from the monomer (B) is 60.0 to 98.5 mass% in the copolymer (P).
  7. The copolymer for a binder for a non-aqueous battery electrode according to any one of claims 3 to 6, wherein the content of a structure derived from the monomer (D) is 0.5 to 60.0 mass% in the copolymer (P).
  8. A slurry for producing a non-aqueous battery electrode, the slurry comprising: the copolymer for a binder for a non-aqueous battery electrode according to any one of claims 1 to 7; an electrode active material; and an aqueous medium.
  9. The slurry for producing a non-aqueous battery electrode according to claim 8, wherein the electrode active material is a negative electrode active material.
  10. The slurry for producing a non-aqueous battery electrode according to claim 8 or 9, wherein a content of the copolymer (P) is 0.1 to 5.0 mass% with respect to total mass of the electrode active material and the copolymer (P).
  11. A non-aqueous battery electrode, comprising: a current collector; and an electrode active material layer formed on a surface of the current collector, wherein the electrode active material layer comprises the copolymer for a binder for a non-aqueous battery electrode according to any one of claims 1 to 7, and an electrode active material.
  12. The non-aqueous battery electrode according to claim 11 wherein the electrode active material is a negative electrode active material.
  13. A non-aqueous battery comprising the non-aqueous battery electrode according to claim 11 or 12.

Description

TECHNICAL FIELD The present invention relates to a copolymer for a binder for a non-aqueous battery electrode, a slurry for producing a non-aqueous battery electrode, a non-aqueous battery electrode formed by using the slurry for producing a non-aqueous battery electrode, and a non-aqueous battery provided with the non-aqueous battery electrode. BACKGROUND TECHNOLOGY Non-aqueous batteries using non-aqueous electrolytes are superior to aqueous batteries in terms of higher voltage, smaller size, and lighter weight. For this reason, non-aqueous batteries are widely used as power sources for notebook PCs, mobile phones, power tools, and electronic and communications equipment. In recent years, non-aqueous batteries have also been used for electric vehicles and hybrid vehicles from the viewpoint of environmentally friendly vehicle application, but there is a strong demand for higher output, higher capacity, and longer life. As a non-aqueous battery, a lithium ion secondary battery is used as a representative example. A non-aqueous battery includes a positive electrode using a metal oxide or the like as an active material, a negative electrode using a carbon material such as graphite as an active material, and a non-aqueous electrolyte solution containing mainly carbonates or flame-retardant ionic liquids. The non-aqueous battery is a secondary battery in which the battery is charged and discharged by the movement of ions between the positive electrode and the negative electrode. Specifically, the positive electrode is obtained by coating a slurry comprising a metal oxide and a binder on the surface of a positive electrode current collector such as an aluminum foil, drying the slurry-coating current collector, and cutting it to an appropriate size. The negative electrode is obtained by coating a slurry comprising a carbon material and a binder on the surface of a negative electrode current collector such as a copper foil, drying the slurry-coating current collector and cutting it to an appropriate size. The binder is used to bind the active material together and to bind the active material with the current collector in the positive electrode and the negative electrode, thereby preventing the active material from being separated from the current collector. As a binder, a polyvinylidene fluoride (PVDF) binder in which an organic solvent N-methyl-2-pyrrolidone (NMP) is used as a solvent is well known (Patent Document 1). However, the binder has low binding properties between the active materials and between the active materials and the current collector, and a large amount of binder is required for actual use. Therefore, there is a disadvantage that the capacity of the non-aqueous battery is reduced. In addition, since NMP, which is an expensive organic solvent, is used for a binder, there are also problems in the price of the final product and in the maintenance of the working environment during the preparation of the slurry or the current collector. As a method for solving these problems, a water-dispersible binder has been conventionally developed, and, for example, a styrene-butadiene rubber (SBR)-based water dispersion in which carboxymethylcellulose (CMC) is used in combination as a thickener is known (Patent Document 2). Since the SBR-based dispersion is an aqueous dispersion, it is inexpensive and advantageous from the viewpoint of conserving the working environment. Further, the active materials and the current collector have relatively good binding properties. Therefore, the electrode can be produced in a smaller amount than that of the PVDF-based binder, and the non-aqueous battery can have a higher output and a higher capacity. Therefore, SBR-based dispersions are widely used as binders for non-aqueous battery electrodes. However, since the SBR-based binder needs to be used in combination with carboxymethyl cellulose as a thickener, the slurry preparation process is complicated. In addition, when using this binder, there is a problem that the binding properties between the active materials and between the active materials and the current collector are insufficient, and when the electrode is produced with a small amount of binder, a part of the active material is peeled off in the process of cutting the current collector. Patent Document 3 discloses an adhesive composition for a patch material containing a sodium acrylate-N-vinylacetamide copolymer (copolymerization ratio: sodium acrylate/N-vinylacetamide = 40/60 by mass). Patent Document 4 discloses a composition for a hydrous gel containing a sodium acrylate-N-vinylacetamide (55/45 (molar ratio)) copolymer. These sodium acrylate-N-vinylacetamide copolymers contain many components derived from N-vinylacetamide. When such a polymer was mixed with a negative electrode active material (difficult-to-graphitize carbon) and water to form a slurry for producing a non-aqueous battery electrode, aggregates were present in the slurry, and the internal resistance o