Positive electrode active material for electric device, positive electrode for electric device, and electric device

A positive electrode active material for an electric device, the positive electrode active material comprising:

• a first active material composed of a transition metal oxide represented by compositional formula (1):
• Li1.5[NiaCobMnc[Li]d]O3 (1)
• wherein Li is lithium, Ni is nickel, Co is cobalt, Mn is manganese, O is oxygen, a, b, c and d satisfy relationships:
• 0.1≦d≦0.4;
• a+b+c+d=1.5;
• and 1.1≦a+b+c≦1.4, the first active material having:
• a layered crystal structure region that has been changed to a spinel type crystal structure by performing charge or charge/discharge in a potential range of 4.3V or more to 4.8V or less with a spinel type crystal structure change ratio of 0.25 or more to less than 1.0, the spinel type crystal structure change ratio representing an amount of Li2MnO3 type crystal structure that is changed to spinel LiMn2O4 type crystal structure in the layered structure;
• and
• a layered crystal structure region that is not changed to the spinel type crystal structure;
• and
• a second active material composed of a spinel-type transition metal oxide represented by compositional formula (2) and having a crystal structure belonging to a space group Fd-3m:
• LiMa′Mn2−a′O4 (2)
• wherein, in formula (2), Li is lithium, M is at least one selected from the group consisting of aluminum, magnesium and chromium, Mn is manganese, O is oxygen, and a′ satisfies a relationship:
• 0≦a′≦0.5, wherein:
• a content ratio of the first active material and the second active material satisfies, in a mass ratio, a relationship represented by expression (3):
• 100:0<MA:MB<0:100 (3)
• wherein MA is a mass of the first active material, and MB is a mass of the second active material;
• a BET specific surface of the first active material is 0.8 m2/g or more to 10.0 m2/g or less;
• and
• a median diameter of the first active material is 20 μm or less.