Active material, electrode, nonaqueous electrolyte secondary battery, battery pack and production method of active material
The active material for a nonaqueous electrolyte secondary battery of the present embodiment includes a core particle and a carbon layer. The core particle is formed of silicon particles having a twinned crystal in part of a surface. The carbon layer coats the core particle.
1. An active material, comprising:
a core particle which is formed of one or more silicon particles having a twinned crystal in part of a surface; and
a carbon layer which coats the core particle.
2. The active material according to claim 1 , wherein the core particle has a silicon particle group formed by bonding the one or more silicon particles.
3. The active material according to claim 1 , further comprising:
a silicon compound layer in part of a space between the one or more silicon particles and the carbon layer.
4. The active material according to claim 3 , wherein the silicon compound layer comprises a carbon-containing silicon compound.
5. The active material according to claim 3 , wherein a thickness of the silicon compound layer is within a range of 1 nm or more and 10 nm or less.
6. An electrode, comprising:
a current collector; and
an active material supported on one surface or both surfaces of the current collector,
wherein the active material is the active material according to claim 1 .
7. A nonaqueous electrolyte secondary battery, comprising the electrode according to claim 6 .
8. A battery pack, comprising the nonaqueous electrolyte secondary battery according to claim 7 .
9. A production method of the active material according to claim 1 , the method comprising:
pretreating, by subjecting one or more silicon microparticles to a thermal treatment at a temperature of 1000° C. to 1300° C., to thereby form a silicon-sintered body in which the one more silicon microparticles are bonded in a form of twinned crystal;
forming a slurry, by mixing the silicon-sintered body with a carbon material and crushing the silicon-sintered body to obtain crushed particles, to thereby form a slurry containing the crushed particles and the carbon material;
performing a complexing, in which the slurry is fired to form a complex of the crushed particles and a carbon precursor; and
firing, in which the complex is fired for 10 minutes to 12 hours at a temperature of 700° C. to 1200° C.
10. The active material according to claim 1 , wherein the one or more silicon particles do not contain a silicon compound.