Negative active material, method for preparing the same, and related secondary battery, battery module, battery pack and apparatus

1. A negative active material comprising a core material and a polymer-modified coating layer on at least a part of its surface, wherein the core material comprises one or more of silicon-based material and tin-based materials; the coating layer comprises sulfur element and carbon element; in a Raman spectrum of the negative active material, the negative active material has scattering peaks at the Raman shifts of 900 cm −1 ˜960 cm −1 , 1300 cm −1 ˜1380 cm −1 and 1520 cm −1 ˜1590 cm −1 , respectively, in which the scattering peak at the Raman shift of 900 cm −1 ˜960 cm −1 has a peak intensity recorded as I l , the scattering peak at the Raman shift of 1520 cm −1 ˜1590 cm −1 has a peak intensity recorded as I G , and I l and I G satisfy 0.2≤I l /I G ≤0.8.

2. The negative active material according to claim 1 , wherein I l and I G satisfy 0.22≤I l /I G ≤0.6.

3. The negative active material according to claim 1 , wherein the negative active material has a Raman spectrum comprising a scattering peak at the Raman shift of 1300 cm −1 ˜1380 cm −1 , in which the scattering peak at the Raman shift of 1300 cm′!˜1380 cm′! has a peak intensity recorded as I D , and I D and I G satisfy 1.05≤I D /I G ≤1.50.

4. The negative active material according to claim 1 , wherein a full width at half maxima of the scattering peak at the Raman shift of 1300 cm −1 ˜1380 cm −1 in the Raman spectrum of the negative active material is from 120 cm −1 to 160 cm −1 .

5. The negative active material according to claim 1 , wherein a mass percentage of the sulfur element in the negative active material is from 0.5% to 3%; and/or,

a mass percentage of the carbon element in the negative active material is from 0.1% to 4%.

6. The negative active material according to claim 1 , wherein the negative active material has an X-ray diffraction pattern comprising a diffraction peak at the diffraction angle 2 8 of 19° to 27° and the diffraction peak has a full width at half maxima of 4° to 12°.

7. The negative active material according to claim 1 , wherein the particle size distribution of the negative active material satisfies: 0.5≤(D v 90−D v 10)/D v 50≤2.5.

8. The negative active material according to claim 1 , wherein the negative active material has a volume average particle diameter D v 50 of from 2 μm-12 μm, and/or

the negative active material has a specific surface area of from 0.5 m 2 /g-5 m 2 /g.

9. The negative active material according to claim 1 , wherein the negative active material has a tap density of 0.8 g/cm 3 to 1.3 g/cm 3 ; and/or

the negative active material has a compacted density of 1.2 g/cm 3 to 1.5 g/cm 3 measured under a pressure of 5 tons (equivalent to 49 KN).

10. The negative active material according to claim 1 , wherein the silicon-based material is selected from one or more of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen compounds, and silicon alloys; optionally, the silicon-based material is selected from silicon-oxygen compounds;

the tin-based material is selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

11. A method for preparing the negative active material according to claim 1 , comprising the following steps:

providing a solution containing a polymer;

mixing a core material with the solution to obtain a mixed slurry, wherein the core material comprises one or more of silicon-based materials and tin-based materials;

drying the mixed slurry under an inert atmosphere to obtain a solid powder;

mixing the solid powder with sulfur powder and performing a heat treatment in an inert atmosphere to obtain a negative active material.

12. The method according to claim 11 , wherein the polymer comprises one or more of polyaniline, polyacetylene, polyacrylonitrile, polystyrene, polyvinyl chloride, and polyethylene.

13. The method according to claim 11 , wherein, in the solution containing the polymer, the ratio of the mass of the polymer to the volume of the solvent is from 0.1 g/L to 10 g/L.

14. The method according to claim 11 , wherein a mass ratio of the core material to the polymer in the mixed slurry is from 10 to 200.

15. The method according to claim 11 , wherein the step of mixing the solid powder and the sulfur powder satisfies: the ratio of the mass of the sulfur powder to the mass of the polymer in the solid powder is from 1 to 5.

16. The method according to claim 11 , wherein the heat-treatment temperature is from 200° C. to 450° C.

17. The method according to claim 16 , wherein the heat-treatment time is from 2 h to 8 h.

18. A secondary battery comprising the negative active material according to claim 1 .