Patent ID: 7128998

Claim:
A nonaqueous electrolyte secondary battery, comprising: an electrode group prepared by winding spirally or in a flattened shape a laminate structure including a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes; and a nonaqueous electrolyte held by the electrode group; wherein an edge portion of the separator in a direction perpendicular to a winding direction protrudes outward from edges of the positive and negative electrodes in the direction perpendicular to the winding direction, and the separator satisfies conditions given by formulas (1) to (3) given below: 0 ≦X 1≦( Y 1/1.5)≦10 (1) X2≦10 (2) X 2 ≦Y 2 ≦20 (3) where Y 1 represents a thermal shrinking rate (%) in the winding direction at 90° C. of the separator, X 1 represents a thermal shrinking rate (%) in the direction perpendicular to the winding direction at 90° C. of the separator, Y 2 represents a thermal shrinking rate (%) in the winding direction at 110° C. of the separator, and X 2 represents a thermal shrinking rate (%) in the direction perpendicular to the winding direction at 110° C. of the separator.