Lithium ion secondary battery and method for manufacturing lithium ion secondary battery

A method of manufacturing a lithium ion secondary battery, wherein the lithium ion secondary battery includes:

• a power generation element having electrode plates each having a current collector and an active material layer that covers part of the current collector, the electrode plates being rolled together with a separator interposed therebetween, the power generation element configured to perform charging and discharging;
• and
• electrode terminals extending along an exposed region on the current collector that is not covered by the active material layer, the electrode terminals being welded to the current collector in a welded region that is included within the exposed region, wherein
• within a two-dimensional flat surface onto which the power generation element is projected, when a ratio La/Lb of a length La to a length Lb is defined as a first ratio and a ratio of Sa/Sb of an area Sa of the welded region to an area Sb of the exposed region is defined as a second ratio, the length La being a length from an end portion of the exposed region overlapping with the electrode terminal to a position in which the welded region is formed in a direction in which the electrode terminal extends, the length Lb being a length of the exposed region in the direction in which the electrode terminal extends,
• the first and second ratios are set to be positioned within a region surrounded by lines connecting five points P1 to P5 in a coordinate system in which the first and second ratios are taken as respective coordinate axes thereof,
• where the point P1 has a first ratio of 0.273 and a second ratio of 0.099,
• the point P2 has a first ratio of 0.636 and a second ratio of 0.099,
• the point P3 has a first ratio of 0.836 and a second ratio of 0.496,
• the point P4 has a first ratio of 0.545 and a second ratio of 0.496, and
• the point P5 has a first ratio of 0.236 and a second ratio of 0.215.