Patent ID: 7700234

Claim:
A binder for electrode of lithium ion secondary battery, which comprises a copolymer comprising: 15 to 80 weight % of units from an ethylenically unsaturated monomer (A) whose homopolymerization yields a polymer soluble in N-methylpyrrolidone (NMP); and 20 to 85 weight % of units from an ethylenically unsaturated monomer (B) whose homopolymerization yields a polymer insoluble in NMP; which copolymer exhibits a swelling degree of 4 or below in an electrolyte obtained by dissolving LiPF 6 in the concentration of 1 mole/liter into a solvent of 1:2 (volume ratio at 20° C.) mixture of ethylene carbonate (EC) and diethyl carbonate (DEC).