Positive electrode active material for electric device, positive electrode for electric device, and electric device
A positive electrode active material is provided for an electric device that contains a first active material comprising a transition metal oxide represented by formula (1): Li1.5[NiaCobMnc[Li]d]O3 (where a, b, c, and d satisfy the relationships: 0<d<0.5; a+b+c+d=1.5; and 1.0<a+b+c<1.5); and a second active material comprising a spinel transition metal oxide that has a crystal structure assigned to the space group Fd-3m, represented by formula (2): LiMa′Mn2−a′O4 (where M indicates at least one metal element having an atomic valence of 2-4, and a′ satisfies the relationship 0=a′<2.0). The fraction content of the first and second active material by mass ratio satisfies the relationship (3): 100:0 A:MB A indicates the mass of the first active material and MB indicates the mass of the second active material).
1. 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):
Li 1.5 [Ni a Co b Mn c [Li] d ]O 3 (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 Li 2 MnO 3 type crystal structure that is changed to spinel LiMn 2 O 4 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:
LiM a′ Mn 2−a′ O 4 (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<M A :M B <0:100 (3)
wherein M A is a mass of the first active material, and M B is a mass of the second active material;
a BET specific surface of the first active material is 0.8 m 2 /g or more to 10.0 m 2 /g or less; and
a median diameter of the first active material is 20 μm or less.
2. The positive electrode active material for an electric device according to claim 1 , wherein the content ratio of the first active material and the second active material satisfies, in the mass ratio, a relationship represented by expression (4):
100:0<M A :M B <50:50 (4)
wherein M A is the mass of the first active material and M B is the mass of the second active material.
3. The positive electrode active material for an electric device according to claim 1 , wherein the content ratio of the first active material and the second active material satisfies, in the mass ratio, a relationship represented by expression (5):
100:0<M A :M B <85:15 (5)
wherein M A is the mass of the first active material and M B is the mass of the second active material.
4. The positive electrode active material for an electric device according to claim 1 , wherein, in the formula (1), a, b, c and d of the first active material satisfy relationships: 0.15≦d≦0.25; a+b+c+d=1.5; and 1.25≦a+b+c≦1.35.
5. The positive electrode active material for an electric device according to claim 1 ,
wherein, in the formula (1), a, b, c and d of the first active material satisfy relationships: 0.15≦d≦0.25; a+b+c+d=1.5; and 1.25≦a+b+c≦1.35, and
the spinel structure change ratio is 0.65 or more to 0.85 or less.
6. The positive electrode active material for an electric device according to claim 1 , wherein a BET specific surface of the second active material is 0.2 m 2 /g or more to 3.0 m 2 /g or less, and
a median diameter of the second active material is 20 μm or less.
7. The positive electrode active material for an electric device according to claim 1 , wherein the first active material and the second active material satisfy a relationship represented by expression (6):
0<M B /(M A +M B )<0.45 (6)
wherein M A is the mass of the first active material and M B is the mass of the second active material.
8. A positive electrode for an electric device, comprising: the positive electrode active material according to claim 1 .
9. An electric device, comprising: the positive electrode for an electric device according to claim 8 .
10. The electric device according to claim 9 , wherein the electric device is a lithium ion secondary battery.