Patent ID: 8758917

Claim:
A secondary battery comprising: a wound electrode body comprising a strip-shaped positive electrode sheet, a strip-shaped negative electrode sheet, and a strip-shaped separator, the positive and negative electrode sheets stacked and wound with the separator interposed therebetween; and a battery case enclosing the wound electrode body, the positive electrode sheet comprising: a strip-shaped positive electrode current collector; an uncoated portion provided in the positive electrode current collector along one lateral-side edge of the positive electrode current collector; and a positive electrode mixture layer comprising a positive electrode mixture, coated on both surfaces of the positive electrode current collector except the uncoated portion and containing a positive electrode active material; the negative electrode sheet comprising: a strip-shaped negative electrode current collector; an uncoated portion provided in the negative electrode current collector along one lateral-side edge of the negative electrode current collector; and a negative electrode mixture layer comprising a negative electrode mixture, coated on both surfaces of the negative electrode current collector except the uncoated portion so as to be wider than the positive electrode mixture layer and containing a positive electrode active material; wherein the positive electrode sheet and the negative electrode sheet are opposed to each other so that the positive electrode mixture layer is covered by the negative electrode mixture layer, and the positive electrode sheet and the negative electrode sheet are stacked on each other so that the uncoated portion of the positive electrode sheet and the uncoated portion of the negative electrode sheet protrude in opposite lateral directions from the separator; wherein the wound electrode body is wound around a winding axis set in a lateral direction of the stacked positive electrode sheet; wherein the battery case has sidewalls facing toward respective side ends of the wound electrode body, the side ends being at opposite lateral sides of the positive electrode sheet, and of the sidewalls of the battery case, one of the sidewalls facing toward the uncoated portion of the positive electrode sheet is thicker than the other one of the sidewalls; and wherein the positive electrode current collector has a thermal conductivity less than that of the negative electrode current collector.