A lithium secondary battery comprising: a positive electrode plate which is a lithium complex oxide sintered plate; a negative electrode layer which has a size larger than the size of the positive electrode plate and contains carbon; a separator which is interposed between the positive electrode plate and the negative electrode layer and has a size larger than the sizes of the positive electrode plate and the negative electrode layer; an electrolytic solution with which the positive electrode plate, the negative electrode layer, and the separator are impregnated; and a pair of exterior films having outer peripheral edges sealed with each other to form an internal space, the internal space accommodating the positive electrode plate, the negative electrode layer, the separator, and the electrolytic solution, wherein the separator has an outer peripheral portion in close contact with at least the outer peripheral edge of the exterior film on the positive electrode plate side or a peripheral region in the vicinity thereof, so as to separate a compartment accommodating the positive electrode and a compartment accommodating the negative electrode from each other, wherein the lithium secondary battery comprises: a body in which a multi-layer structure including the positive electrode plate, the separator, the negative electrode layer, and the pair of exterior films exists throughout the entire area of the body; and an outer extension which is located outwardly of the outer peripheral edge of the positive electrode plate and includes the separator, the negative electrode layer, and the pair of exterior films, wherein the portions of the negative electrode layer and the separator corresponding to the outer extension are deviated toward the positive electrode plate side from the portions of the negative electrode layer and the separator corresponding to the body, wherein the portions of the negative electrode layer and the separator corresponding to the outer extension enter the outer region around the positive electrode plate, and wherein the positive electrode plate has a thickness of 70 to 120 μm and the negative electrode layer has a thickness of 70 to 160 μm. a positive electrode plate which is a lithium complex oxide sintered plate; a negative electrode layer which has a size larger than the size of the positive electrode plate and contains carbon; a separator which is interposed between the positive electrode plate and the negative electrode layer and has a size larger than the sizes of the positive electrode plate and the negative electrode layer; an electrolytic solution with which the positive electrode plate, the negative electrode layer, and the separator are impregnated; and a pair of exterior films having outer peripheral edges sealed with each other to form an internal space, the internal space accommodating the positive electrode plate, the negative electrode layer, the separator, and the electrolytic solution, wherein the separator has an outer peripheral portion in close contact with at least the outer peripheral edge of the exterior film on the positive electrode plate side or a peripheral region in the vicinity thereof, so as to separate a compartment accommodating the positive electrode and a compartment accommodating the negative electrode from each other, wherein the lithium secondary battery comprises: a body in which a multi-layer structure including the positive electrode plate, the separator, the negative electrode layer, and the pair of exterior films exists throughout the entire area of the body; and an outer extension which is located outwardly of the outer peripheral edge of the positive electrode plate and includes the separator, the negative electrode layer, and the pair of exterior films, wherein the portions of the negative electrode layer and the separator corresponding to the outer extension are deviated toward the positive electrode plate side from the portions of the negative electrode layer and the separator corresponding to the body, a body in which a multi-layer structure including the positive electrode plate, the separator, the negative electrode layer, and the pair of exterior films exists throughout the entire area of the body; and an outer extension which is located outwardly of the outer peripheral edge of the positive electrode plate and includes the separator, the negative electrode layer, and the pair of exterior films, wherein the portions of the negative electrode layer and the separator corresponding to the outer extension are deviated toward the positive electrode plate side from the portions of the negative electrode layer and the separator corresponding to the body, wherein the portions of the negative electrode layer and the separator corresponding to the outer extension enter the outer region around the positive electrode plate, and wherein the positive electrode plate has a thickness of 70 to 120 μm and the negative electrode layer has a thickness of 70 to 160 μm.