Lithium ion secondary battery

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 said porous film comprises a plurality of films and a content of said resin binder in the total of said filler and said resin binder contained in a film positioned at said second surface side is higher than a content of said resin binder in the total of said filler and said resin binder contained in a film positioned at said first surface side.