Patent ID: 8211574

Claim:
A lithium ion secondary battery comprising: a positive electrode for absorbing and desorbing lithium ion; a negative electrode for absorbing and desorbing lithium ion; a porous film interposed between said positive electrode and said negative electrode, the porous film having a thickness of 0.5 to 20 μm; a sheet separator interposed between said positive electrode and said porous film, the sheet separator having a thickness of 8 to 25 μm and being made of a polyolefin resin; and a non-aqueous electrolyte; wherein said porous film is adhered to a surface of at least said negative electrode, a total thickness of said sheet separator and said porous film is 15 to 30 μm, said porous film comprises an inorganic tiller and a first binder, said inorganic filler having an alkaline site on the surface thereof, a content of said first binder in said porous film being 1.5 to 4 parts by weight per 100 parts by weight of said filler, said first binder comprises core-shell type particles of acrylonitrile-acrylate copolymer having a polyacrylonitrile chain as a first rubber, said first rubber being water-insoluble and having a decomposition temperature of 250° C. or higher, said core-shell type particles each having an acidic group on the surface thereof, said acidic group bonding with the alkaline site of said inorganic filler, said negative electrode comprises a negative electrode active material for absorbing and desorbing lithium ion and a second binder, said second binder includes a second rubber particle comprising a polymer including a styrene unit and a butadiene unit, and a water-soluble polymer comprising a polymer including a methylcellulose unit, and a content of said second binder in said negative electrode is 1.5 to 3 parts by weight per 100 parts by weight of said negative electrode active material.