Binder composition for lithium ion secondary battery electrodes and use thereof

• US 6,770,397 B1
• Filed: 01/14/2002
• Issued: 08/03/2004
• Est. Priority Date: 07/15/1999
• Status: Active Grant

• Current Assignee: ZEON Corporation
• Original Assignee: ZEON Corporation
• Inventors: Yamakawa, Masahiro, Nakamura, Katsuya, Takano, Fumio, Maeda, Kouichirou
• Primary Examiner(s): Harlan, Robert D.
• Application Number:
  US10/030,086
• Time in Patent Office: 932 Days
• Field of Search: 429/217, 429/209, 429/213, 429/214, 429/215, 429/216, 249/231.95, 526/319, 252/182.1
• US Class Current: 429/217
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 4/621 Binders
• CPC Class Codes: H01M 4/622 being polymers
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A binder composition comprising a polymer dispersed in a liquid dispersion medium, wherein the polymer comprises structural units represented by the following formula:

wherein R¹ is hydrogen, C1-4 alkyl group, or halogen, R² is C1-20 alkyl group or C6-30 aryl group, R³ and R⁴ are hydrogen or methyl group, provided that R³ and R⁴ are not simultaneously methyl group, and n is an integer of 1-50. A lithium ion secondary battery having an electrode made by using this binder composition exibibits excellent characteristics at repetition of a charge-discharge cycle.

Claims

1. A binder composition for an electrode for a lithium-ion secondary battery, comprising a polymer and a liquid dispersion medium;

characterized in that said polymer comprises structural units represented by the following general formula (1) and is dispersed in the liquid dispersion medium;

wherein R¹ is hydrogen, a straight chain or branched alkyl group having 1 to 4 carbon atoms, or halogen, R² is a straight chain, branched or cyclic alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 30 carbon atoms, R³ and R⁴ are hydrogen or a methyl group, provided that R³ and R⁴ are not simultaneously a methyl group, and n is an integer of 1 to 50; and

said polymer has a gel content of 50% to 100%, as calculated as a ratio in % of insoluble matter to an electrolyte solution, which is a one mole/liter solution of LiPF₆ in a mixed solvent comprised of ethylene carbonate/diethyl carbonate at a ratio of 50/50 by volume as measured at 20°

C.

2. The binder composition according to claim 1, wherein said polymer comprises 0.1 to 100% by weight of the structural units of formula (1), 0 to 99.9% by weight of acrylic acid ester or methacrylic acid ester structural units represented by the following formula (3), 0 to 50% by weight of structural units derived from a polar monomer and 0 to 20% by weight of units derived from a crosslinking monomer:

wherein R⁵ is hydrogen or a methyl group, and R⁶ is an alkyl group having 1 to 20 carbon atoms.

3. The binder composition according to claim 2, wherein the polar monomer is at least one monomer selected from the group consisting of cyano group-containing monoethylenically unsaturated monomers, alkyl acrylate and alkyl methacrylate monomers, the alkyl group having 1 to 20 carbon atoms and having at least one substituent selected from the group consisting of a hydroxyl group, an amino group and alkylamino groups, and ethylenically unsaturated monocarboxylic acids.

4. The binder composition according to claim 1, wherein the content of the polymer is in the range of 0.2 to 80% by weight based on the weight of the binder composition.

5. The binder composition according to claim 1, wherein the liquid dispersion medium is a dispersion medium having a boiling point of 80 to 350°

C. at normal pressure.

6. The binder composition according to claim 1, wherein the polymer has a gel content of 50 to 100% in the liquid dispersion medium.

7. A slurry for an electrode for a lithium-ion secondary battery, characterized by comprising a binder composition as claimed in claim 1, and an active material.

8. The slurry for an electrode according to claim 7, wherein the amount of the active material is in the range of 1 to 1,000 times by weight of the amount of the solid content in the binder composition.

9. An electrode for a lithium-ion secondary battery, characterized as being made by coating a collector with a slurry as claimed in claim 8, and then drying a coating of the slurry.

10. The electrode for a lithium-ion secondary battery according to claim 9, which has an active material layer having a thickness of 0.005 to 5 mm.

11. A lithium-ion secondary battery, characterized in that one of a positive and a negative electrode of the battery is an electrode as claimed in claim 9.