Various materials are known to be used as positive electrode active materials of secondary batteries, and further a secondary battery in which a plurality of materials are used as positive electrode active materials is also known.
For example, Patent Literature 1 and 2 each specifically discloses a lithium ion secondary battery in which LiNi1/3CO1/3Mn1/3O2 and LiFePO4 are used as positive electrode active materials. Patent Literature 3 specifically discloses a lithium ion secondary battery in which LiNi0.8CO0.1Mn0.1O2 and LiV2/3PO4 are used as positive electrode active materials.
These literature states that LiNi1/3Co1/3Mn1/3O2 or LiNi0.8Co0.1Mn0.1O2 is a positive electrode active material having a high capacity, and LiFePO4 or LiV2/3PO4 is a positive electrode active material having excellent safety. In these literature, in producing a specific lithium ion secondary battery, blending ratios of the two types of the positive electrode active materials are defined on a mass basis.
Here, a battery having a higher blending ratio of LiFePO4 or LiV2/3PO4, which has excellent safety, is considered to have higher safety.