Active material, nonaqueous electrolyte battery, and battery pack
According to one embodiment, there is provided an active material including monoclinic niobium titanium composite oxide particles and a carbon material layer. The monoclinic niobium titanium composite oxide particles can absorb and release Li ions or Na ions and satisfy Formula (1) below. The carbon material layer covers at least a part of surfaces of the niobium titanium composite oxide particles and satisfies Formula (2) below: 0.5≤(α/β)≤2 (1) 0≤(γ/σ)≤0.1 (2)
1. An active material, comprising:
monoclinic niobium titanium composite oxide particles which satisfy formula (1) and are capable of absorbing and releasing Li ions or Na ions; and
a carbon material layer which covers at least a part of surfaces of the niobium titanium composite oxide particles and satisfies formula (2):
0.5≤(α/β)≤2 (1)
0≤(γ/σ)≤0.1 (2)
wherein
in the formula (1), α represents a mole number of Nb of the niobium titanium composite oxide particles and β represents a mole number of Ti of the niobium titanium composite oxide particles,
in the formula (2), γ represents a number of hydrogen atoms in the carbon material layer and σ represents a number of carbon atoms in the carbon material layer,
an average primary particle diameter of the monoclinic niobium titanium composite oxide particles covered with the carbon material layer ranges from 0.1 to 1 μm, and
the niobium titanium composite oxide particles comprise a monoclinic niobium titanium composite oxide represented by A x TiM y Nb 2−y O 7±z , wherein 0≤x≤5, 0≤y≤0.5, −0.3≤z≤0.3, M represents at least one kind of metal other than Ti and Nb, and A represents Li or Na.
2. The active material according to claim 1 , wherein the M is at least one metal selected from the group consisting of Mg, Al, V, Fe, Mo, Sn, and W.
3. The active material according to claim 1 , wherein:
0.8≤(α/β)≤1.9
0≤(γ/σ)≤0.05.
4. The active material according to claim 1 , wherein an amount of the carbon material layer is from 0.1 to 5% by weight.
5. A nonaqueous electrolyte battery, comprising:
a positive electrode;
a negative electrode comprising the active material according to claim 1 ; and
a nonaqueous electrolyte.
6. The battery according to claim 5 , wherein the positive electrode comprises at least one selected from the group consisting of lithium iron phosphate having an olivine crystal structure, lithium manganese phosphate, lithium manganese iron phosphate, fluorinated lithium iron sulfate, lithium nickel cobalt manganese oxide, and lithium manganese oxide having a spinel crystal structure.
7. The battery according to claim 5 , wherein the positive electrode comprises at least one member selected from the group consisting of LiFePO 4 , LiMnPO 4 , LiMn 1−x Fe x PO 4 where 0<x≤0.5, LiFeSO 4 F, LiNi a Co b Mn 1−a−b O 2 where 0<a<1, 0<b<1, and 0<(1−a−b)<1, LiMn 2 O 4 , and LiMn 1.5 Ni 0.5 O 4 .
8. A battery pack, comprising:
the nonaqueous electrolyte battery according to claim 5 .
9. A vehicle, comprising:
the battery pack according to claim 8 .
10. The active material according to claim 1 , wherein
0<(γ/σ)≤0.1.
11. The active material according to claim 1 , wherein
0.01≤(γ/σ)≤0.1.
12. The active material according to claim 1 , wherein
0.8≤(α/β)≤1.875.
13. The active material according to claim 1 , wherein the monoclinic niobium titanium composite oxide particles covered with the carbon material layer have an average primary particle diameter of from 0.1 to 0.3 μm.
14. The active material according to claim 1 , wherein the monoclinic niobium titanium composite oxide particles covered with the carbon material layer have an average secondary particle diameter of from 1 to 3 μm.
15. The active material according to claim 1 , wherein the monoclinic niobium titanium composite oxide particles covered with the carbon material layer have an average secondary particle diameter of from 1 to 20 μm.