abstract |
A lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode has a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. The negative electrode current collector satisfies: n ( D 2/ D 1)≥0.968 (1),n n D 2≥21.947*( X/ 100)−24.643 (2),n n 110≤X≤125 (3), andn n where D1 is a first displacement amount in a first piercing test at a first piercing speed of 0.1 mm/min or more; D2 is a second displacement amount in a second piercing test at a second piercing speed of less than 0.1 mm/min; and X is an expansion coefficient (%) of the negative electrode active material layer. |