Patent ID: 7638230

Claim:
A lithium ion secondary battery comprising: an electrode group comprising a belt-shaped positive electrode and a belt-shaped negative electrode that are wound with a separator interposed therebetween; and a can with a bottom for accommodating said electrode group, wherein said positive electrode includes a positive electrode current collector and a positive electrode mixture layer carried on said positive electrode current collector, said negative electrode includes a negative electrode current collector and a negative electrode mixture layer carried on said negative electrode current collector, a porous heat-resistant layer is partially provided between said separator and at least one of said positive electrode mixture layer and said negative electrode mixture layer, said porous heat-resistant layer is positioned along at least one side of at least one of said positive electrode mixture layer and said negative electrode mixture layer, and is provided from an edge of winding initiation side to a given position on at least one of said positive electrode mixture layer and said negative electrode mixture layer, and when the area of said porous heat-resistant layer is represented by A and the area of said mixture layer is represented by B, the ratio A/B of the area A to the area B is 0.02 to 0.3.