| abstract |
A lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution, wherein the positive electrode includes a first lithium composite oxide and a second lithium composite oxide expressed by the following equation (1), as a positive electrode active material, and a charge capacity (vs lithium metal) per unit volume during a charge and discharge of a first cycle is larger in the second lithium composite oxide compared to the first lithium composite oxide, and a discharge voltage (vs lithium metal) during the charge and discharge of the first cycle is lower in the second lithium composite oxide compared to the first lithium composite oxide, Li 1+a (Mn b Co c Ni 1-b-c ) 1-a O 2 . . . ( 1 ), where a, b, and c satisfy relationships of 0<a≦0.25, 0.5≦b<0.7, and 0≦c<1−b. |