Patent ID: 7758998

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 8 parts by weight per 100 parts by weight of said filler, and an amount of said resin binder is smaller in a first surface side where said porous film is in contact with said surface of said electrode, and larger in a second surface side opposite to said first surface side, wherein a content of said filler in the total of said filler and said resin binder contained in a surface portion of said second surface side of said porous film is 70 to 98 wt %, and a thickness of said surface portion is 20% of the thickness of said porous film.