The present embodiment provides a lithium ion secondary battery including a positive electrode containing LiaNixCoyMzO2 (0.9≤a≤1.2, 0.3≤x≤0.8, 0.2≤y+z≤0.7, where M is a metal element other than Li, Ni, and Co) as a positive active material, and a negative electrode containing non-graphitic carbon as a negative active material. In this lithium ion secondary battery, at a portion where the positive electrode and the negative electrode face each other, a basis weight (P) of the positive active material and a basis weight (N) of the negative active material satisfy a relational expression of 0.65≤P/N≤1.05.