LITHIUM ION SECONDARY BATTERY

摘要

PROBLEM TO BE SOLVED: To suppress the reduction in the initial capacity of a lithium ion secondary battery owing to the variation in separator size.SOLUTION: A lithium ion secondary battery 1 comprises: a positive electrode 12 extending along a first direction; a negative electrode 11 extending along the first direction and facing the positive electrode 12 in a second direction orthogonal to the first direction; and a separator 13 extending along the first direction, provided between the positive electrode 12 and the negative electrode 11, and having crosslinked structure. The separator 13 includes: a first region (13a) facing the positive electrode 12 and the negative electrode 11 in the second direction; and a second region (13b) which is not facing the positive electrode and/or the negative electrode in the second direction. The first region (13a) has a first porosity, and the second region (13b) has a second porosity lower than the first porosity.SELECTED DRAWING: Figure 3