Active material for battery, nonaqueous electrolyte battery, and battery pack

1. An active material, comprising: a niobium composite oxide represented by the formula Li x M (1-y) Nb y Nb 2 O (7+δ) ,

wherein M represents at least one kind selected from the group consisting of Ti and Zr,

x, y, and δ are numbers respectively satisfying the following: 0≤x≤6, 0≤y≤1, and −1≤δ≤1,

wherein carbonate ions are arranged on at least one part of the surface of the active material, and

wherein a content of a carbon originated from the carbonate ions is from 0.01 to 3% by mass based on a total amount of the active material.

2. The active material according to claim 1 , wherein lithium carbonate is arranged on at least one part of the surface of the active material.

3. The active material according to claim 1 , wherein a specific surface area of the active material for a battery is from 0.5 to 50 m 2 /g.

4. The active material according to claim 1 , wherein a specific surface area of the active material for a battery is from 3 to 30 m 2 /g.

5. The active material according to claim 1 , wherein a crystal structure of the niobium composite oxide belongs to a monoclinic system.

6. The active material according to claim 1 , wherein the crystal structure of the niobium composite oxide belongs to a space group C2/m or P12/m1.

7. The active material according to claim 1 , wherein the active material has a peak belonging to the carbonate ion in the range of 1430±30, the range of 1500±30, or the range of 2350±30 cm −1 in an infrared reflectance spectrum with Fourier transform infrared spectrophotometer.

8. A nonaqueous electrolyte battery, comprising:

a positive electrode;

a negative electrode comprising the active material according to claim 1 ; and

a nonaqueous electrolyte.

9. A battery pack, comprising one or more nonaqueous electrolyte batteries according to claim 8 .

10. The battery pack according to claim 9 , wherein a plurality of nonaqueous electrolyte batteries are connected electrically to each other, and the battery pack further comprises a protective circuit that can detect the voltage of each of the nonaqueous electrolyte batteries.

11. The battery pack according to claim 9 , further comprising:

an external energizing terminal.

12. The battery pack according to claim 9 , wherein the nonaqueous electrolyte batteries are connected in series, in parallel or with a combination of series connection and parallel connection.

13. The active material according to claim 1 , wherein the surface of the active material is covered with the carbonate ions.