Active material containing an Nb2TiO7 phase, electrode, secondary battery, battery pack, and vehicle
An active material includes an Nb 2 TiO 7 phase and at least one Nb-rich phase selected from an Nb 10 Ti 2 O 29 phase, an Nb 14 TiO 37 phase, and an Nb 24 TiO 64 phase. The active material satisfies a peak intensity ratio represented by the following Formula (1): 0<I B /I A ≤0.25 (1). In Formula (1), I A is a peak intensity of the maximum peak attributed to the Nb 2 TiO 7 phase and appealing at 2θ of 26.0±0.1° in a wide angle X-ray diffraction pattern under CuKα rays as an X-ray source, and I B is a peak intensity of the maximum peak attributed to the at least one Nb-rich phase and appearing at 2θ of 24.9±0.2° in the diffraction pattern.
1. An active material comprising:
an Nb 2 TiO 7 phase; and
at least one Nb-rich phase selected from a would consisting of an Nb 10 Ti 2 O 29 phase, an Nb 14 TiO 37 phase, and an Nb 24 TiO 64 phase,
wherein the active material comprises mixed-phase active material particles comprising: a shell part formed of the Nb 2 TiO 7 phase; and a core part surrounded by the shell part and formed of the at least one Nb-rich phase,
the mixed-phase active material particles further comprises an intermediate part interposed between the core part and the shell part,
the intermediate part comprises the Nb 2 TiO 7 phase and the at least one Nb-rich phase and has a concentration gradient of the Nb 2 TiO 7 phase rising from a side of the core part to a side of the shell part, and
the active material satisfies a peak intensity ratio represented by Formula (I):
0< I B /I A ≤0.25 (1)
wherein in the Formula (1), I A is a peak intensity of a maximum peak attributed to the Nb 2 TiO 7 phase and appearing at 2θ of 26.0±0.1° in a wide angle X-ray diffraction pattern under a CuKα ray as an X-ray source, and I B is a peak intensity of a maximum peak attributed to the at least one Nb-rich phase and appearing at 2θ of 24.9±0.2° in the diffraction pattern.
2. The active material according to claim 1 , satisfying Formula (2):
0.01≤ I B /I A ≤0.25 (2)
3. The active material according to claim 1 , wherein the Nb 2 TiO 7 phase and the at least one Nb-rich phase interpenetrate each other in at least a part of the intermediate part.
4. An electrode comprising the active material according to claim 1 .
5. The electrode according to claim 4 , wherein the electrode comprises an active material-containing layer comprising the active material.
6. A secondary battery comprising:
a positive electrode;
a negative electrode; and
an electrolyte,
wherein the negative electrode is the electrode according to claim 4 .
7. A battery pack comprising the secondary battery according to claim 6 .
8. The battery pack according to claim 7 , further comprising:
an external power distribution terminal; and
a protective circuit.
9. The battery pack according to claim 7 , comprising
plural of the secondary battery, wherein the secondary batteries are electrically connected in series, in, parallel, or in a combination of in series and in parallel.
10. A vehicle comprising the battery pack according to claim 7 .
11. The vehicle according to claim 10 , which comprises a mechanism configured to convert kinetic energy of the vehicle into regenerative energy.