Patent ID: 7396612

Claim:
A lithium ion secondary battery comprising: a positive electrode capable of absorbing and desorbing lithium ion; a negative electrode capable of absorbing and desorbing lithium ion; a porous film interposed between said positive electrode and said negative electrode; and a non-aqueous electrolyte; wherein said porous film is adhered to a surface of at least one of said positive electrode and said negative electrode, said porous film comprises a filler and a resin binder, a content of said resin binder in said porous film is 1.5 to 4 parts by weight per 100 parts by weight of said filler, and said resin binder comprises a plurality of resin binders including core-shell type rubber particles and other resin binder, said rubber particles have an adhesive surface portion including at least an acrylonitrile unit, an acrylate unit, or a methacrylate unit, said other resin binder comprises at least one selected from the group consisting of fluorocarbon resins, cellulose resins, and polyvinyl pyrrolidone, and the ratio of said core-shell type rubber particles to the total amount of resin binders is 20 to 80 wt. %.