Core shell active material of monoclinic niobium-titanium composite oxide, nonaqueous electrolyte battery and battery pack
According to one embodiment, there is provided an active material. The active material includes particles. Each of the particles includes a core phase and a shell phase surrounding at least a part of the core phase. The core phase includes a first monoclinic niobium-titanium composite oxide. The shell phase includes a second monoclinic niobium-titanium composite oxide. An oxidation number of titanium in the core phase is larger than an oxidation number of titanium in the shell phase, and/or an oxidation number of niobium in the core phase is larger than an oxidation number of niobium in the shell phase.
1. An active material comprising:
particles each comprising
a core phase comprising a first monoclinic niobium-titanium composite oxide represented by a formula of Nb 2 TiO 7 or Nb 2 TiO 7-δ , 0<δ≤0.3, the core being in a form of an aggregate of particles; and
a shell phase comprising a second monoclinic niobium-titanium composite oxide and surrounding at least a part of the core phase, the second monoclinic niobium-titanium composite oxide being represented by a formula of Nb 1.33 Ti 0.67 O 4 ,
wherein the shell phase is a layer partially surrounding the core phase.
2. The active material according to claim 1 , wherein the particles each comprising the core phase and the shell phase have a molar ratio of niobium to titanium Nb/Ti within a range of 0<Nb/Ti≤2.
3. The active material according to claim 1 , further comprising a carbon layer covering the particles each comprising the core phase and the shell phase.
4. A nonaqueous electrolyte battery comprising:
a negative electrode comprising the active material according to claim 1 ;
a positive electrode; and
a nonaqueous electrolyte.
5. A battery pack comprising:
the nonaqueous electrolyte battery according to claim 4 .
6. The battery pack according to claim 5 , further comprising a protective circuit which detects a voltage of the nonaqueous electrolyte battery.
7. A battery pack comprising a plurality of nonaqueous electrolyte batteries, each of the plurality of nonaqueous electrolyte batteries comprising:
a positive electrode;
a negative electrode comprising the active material according to claim 1 ; and
a nonaqueous electrolyte,
wherein the plurality of nonaqueous electrolyte batteries are electrically connected to each other in series and/or parallel.
8. The active material according to claim 1 , wherein a material of the shell phase is a reduced product of a material of the core phase.
9. The active material according to claim 1 , wherein the shell phase has a thickness within a range from 1 nm to 50 nm.
10. The active material according to claim 1 , wherein the shell phase has a thickness corresponding to 0.6% or more and 30% or less with respect to a particle diameter of the particles each comprising the core phase and the shell phase.