| 摘要 |
PROBLEM TO BE SOLVED: To provide a square lithium ion secondary battery having high safety.SOLUTION: Assuming that the width dimension and the height dimension of a battery case 111 are A (mm) and B (mm), respectively, and that the distance from the inner side face of the battery case 111 to a wound electrode body 150 is C (mm), then a combination of a value A/B and a value C (A/B, C) fall inside an inner region G of a square PQRS formed by linking four points (A/B, C)=(1.3,1), (2.2, 2.5), (2.2,7), (1.6,7) with a straight line in that order in a coordinate plane representing the relationship between A/B and C; Young's modulus E1 (GPa) of the case body 111 and a thickness T (mm) of the case body 111 satisfy the relationship E1×T≥28; and a weld penetration depth Dmin (mm) in a portion where a weld penetration depth D is smallest out of a welded section 110b between the case body 111 and a lid member 112 and Young's modulus E2 (GPa) of the welded section 110b satisfy the relationship Dmin×E2≥20. |
