Lithium ion secondary battery

摘要

The present invention intends to provide a lithium ion secondary battery that has a high capacity and excellent charge/discharge cycle characteristics. A lithium ion secondary battery includes: a positive electrode; and a negative electrode, wherein the negative electrode includes a negative electrode active material of which initial charge capacity is 1800 mAh/g or more and initial efficiency (initial discharge capacity/initial charge capacity) is 0.70 to 0.85, the positive electrode includes a positive electrode active material of which initial charge capacity is 160 mAh/g or more and initial efficiency (initial discharge capacity/initial charge capacity) is 0.75 to 0.90, and an initial discharge capacity ratio of the negative electrode and the positive electrode (initial discharge capacity of the negative electrode/initial discharge capacity of the positive electrode) is 0.90 to 1.30.