Negative electrode active material for nonaqueous electrolyte secondary batteries
In order to propose a new negative electrode for nonaqueous electrolyte secondary batteries having excellent dispersibility even with a negative electrode active material having a relatively small particle size, there is proposed a negative electrode active material for nonaqueous electrolyte secondary batteries, the negative electrode active material containing silicon and having negative electrode active material particles that have a D50 based on a volume-based particle size distribution obtainable by measurement by a laser diffraction scattering type particle size distribution analysis method, of 0.1 μm to 5.0 μm, and include a surface layer containing oxygen, silicon and carbon on the entire surface or a portion of the active material surface.
1. A negative electrode active material for nonaqueous electrolyte secondary batteries, the negative electrode active material containing silicon and comprising negative electrode active material particles that have a D50 based on a volume-based particle size distribution obtainable by measurement by a laser diffraction scattering type particle size distribution analysis method, of 0.1 μm to 5.0 μm, and include a surface layer containing oxygen, silicon, and carbon over the entire surface or a portion of the active material surface, and an amount of water per unit specific surface area (120° C. to 300° C.) obtained by following measurement method is 50 ppm/(m 2 /g) to 250 ppm/(m 2 /g);
the measurement method of an amount of water per unit specific surface area comprising: heating the negative electrode active material at temperature increase rate of 10° C./min using a moisture vaporizing apparatus, the amount of water released when the active material is heated to 120° C. to 300° C. is measured using a moisture meter, and then the amount of water released when the active material was heated to 120° C. to 300° C. thus measured and obtained is calculated by dividing by the specific surface area,
wherein the thickness of the surface layer is 0.1 nm to 10 nm, and
the negative electrode active material particles further comprise an intermediate layer between the active material surface and the surface layer, wherein said intermediate layer comprises silicon dioxide as a main component, and said intermediate layer has a thickness of 0.1 nm to 2.0 nm.
2. The negative electrode active material for nonaqueous electrolyte secondary batteries according to claim 1 , wherein a specific surface area is 1.0 m 2 /g to 15.0 m 2 /g.
3. The negative electrode active material for nonaqueous electrolyte secondary batteries according to claim 2 , wherein an amount of carbon in the surface layer is 0.01 wt % to 0.5 wt % of the negative electrode active material particles.
4. The negative electrode active material for nonaqueous electrolyte secondary batteries according to claim 2 , wherein a total content of iron (Fe), aluminum (Al), calcium (Ca), phosphorus (P) and oxygen (O) is 0.1 mass % to 2.5 mass %.
5. The negative electrode active material for nonaqueous electrolyte secondary batteries according to claim 1 , wherein an amount of carbon in the surface layer is 0.01 wt % to 0.5 wt % of the negative electrode active material particles.
6. The negative electrode active material for nonaqueous electrolyte secondary batteries according to claim 5 , wherein a total content of iron (Fe), aluminum (Al), calcium (Ca), phosphorus (P) and oxygen (O) is 0.1 mass % to 2.5 mass %.
7. The negative electrode active material for nonaqueous electrolyte secondary batteries according to claim 1 , wherein a total content of iron (Fe), aluminum (Al), calcium (Ca), phosphorus (P) and oxygen (O) is 0.1 mass % to 2.5 mass %.
8. The negative electrode active material for nonaqueous electrolyte secondary batteries according to claim 1 , wherein the negative electrode active material is obtainable according to a production method that includes a step of surface treating a silicon-containing material having an amount of surface water per unit specific surface area (200° C. to 300° C.) of 0.1 ppm/(m 2 /g) to 20 ppm/(m 2 /g), with a silane coupling agent.
9. The negative electrode active material for nonaqueous electrolyte secondary batteries according to claim 8 , wherein the silane coupling agent includes an organosilicon compound having an amino group in a side chain.
10. A negative electrode for nonaqueous electrolyte secondary batteries, the negative electrode comprising the active material for nonaqueous electrolyte secondary batteries according to claim 1 , and a binder.
11. The negative electrode for nonaqueous electrolyte secondary batteries according to claim 10 , wherein the binder is a polyimide.
12. A nonaqueous electrolyte secondary battery, comprising a negative electrode according to claim 10 .
13. A negative electrode for nonaqueous electrolyte secondary batteries, the negative electrode comprising the active material for nonaqueous electrolyte secondary batteries according to claim 1 as a first negative electrode active material, graphite as a second negative electrode active material, and a binder.