Negative electrode active material for nonaqueous electrolyte secondary battery

1. A negative electrode active material for a secondary battery, comprising:

secondary particles each formed of primary particles bonded to each other,

wherein the primary particles contain carbon material particles and a lithium ion-conductive solid electrolyte which covers the surfaces of the carbon material particles,

wherein the solid electrolyte is a lithium compound,

the lithium compound is a lithium salt of a polyanion including an element M and an element A,

M is at least one selected from the group consisting of P, Si, B, V, Nb, W, Ti, Zr, Al, Ba, La, and Ta, and A is at least one selected from the group consisting of F, S, O, N, and Br,

wherein at each of the interfaces between the carbon material particles and the lithium compound, a compound having an M-C bond is formed, and

wherein the primary particles are bonded to each other by the solid electrolyte interposed therebetween to thereby form the secondary particle.

2. The negative electrode active material for a secondary battery according to claim 1 ,

wherein the lithium compound is a polyoxometalate compound.

3. The negative electrode active material for a secondary battery according to claim 2 ,

wherein the polyoxometalate compound is at least one selected from the group consisting of Li 3 PO 4 , Li 4 SiO 4 , Li 2 Si 2 O 5 , Li 2 SiO 3 , Li 3 BO 3 , Li 3 VO 4 , LiNbO 3 , and Li 3 NbO 4 .

4. The negative electrode active material for a secondary battery according to claim 3 ,

wherein the polyoxometalate compound includes at least Li 4 SiO 4 .

5. The negative electrode active material for a secondary battery according to claim 1 ,

wherein the carbon material particles are at least one selected from the group consisting of graphite and hard carbon.

6. The negative electrode active material for a secondary battery according to claim 1 ,

wherein the average particle diameter of the carbon material particles is 0.5 to 5 μm.

7. The negative electrode active material for a secondary battery according to claim 1 ,

wherein at least some of the carbon material particles are each an aggregate of fine particles.

8. The negative electrode active material for a secondary battery according to claim 1 ,

wherein the porosity P satisfies a relationship: 0≤P<50, the porosity P being calculated by P=100×Ssp/(Ssp+Sen),

where a space region in the secondary particle is Ssp and another region occupied with the primary particles is Sen in the cross-sectional photo of the secondary particle processed by binarization.

9. The negative electrode active material for a secondary battery according to claim 1 ,

wherein the average particle diameter of the secondary particles is 10 to 25 μm.

10. The negative electrode active material for a secondary battery according to claim 1 , wherein the amount of the solid electrolyte contained in the secondary particle with respect to 100 parts by mass of the carbon material particles is 1 to 300 parts by mass.