Patent ID: 7989107

Claim:
A lithium-ion secondary battery which is provided with an electrode group where a positive electrode plate obtained by applying positive electrode mixture mainly including positive electrode active material to a foil and a negative electrode plate obtained by applying negative electrode mixture mainly including negative electrode active material to a foil are disposed so as to sandwich a separator, where an end portion of the foil of at least one of the positive electrode plate and the negative electrode plate projects from an end face of the electrode group, a current collecting member for collecting current from the foil of said at least one of the positive and negative electrode plate is disposed so as to face the end face of the electrode group, and a joint portion obtained by joining the current collecting member and an end portion of the foil is formed so as to project from a face of the current collecting member which faces the electrode group, wherein the current collecting member, which has a disc-like shape which is the same shape as the end face of the electrode group, includes a plurality of projecting ridge portions with an approximately trapezoidal shape in section extending from a central portion of the current collecting member toward an outer edge portion thereof on a face thereof positioned on a side opposite to the electrode group, the current collecting member further having flat portions facing the electrode group which are provided at positions corresponding to the projecting ridge portions, wherein the joint portion between the end portion of the foil and the flat portions is formed from melted ridge portions that project from the flat portions into the end portion of the foil.