Negative active material, preparation method thereof, and related secondary battery, battery module, battery pack and apparatus

1. A method for preparing a negative active material, comprising the following steps (1), (2), (3), optional step (2-1), and optional step (3-1):

(1) dissolving a certain mass of a polymer in a solvent to obtain a solution; wherein the polymer is selected from at least one of polyacrylonitrile, polyaniline, polyethylene, polyacetylene, polyvinyl chloride and polystyrene;

(2-1) crushing SiO x material to obtain SiO x particles with a certain particle size, in which 0<x<2;

(2) mixing the SiO x particles with the solution obtained in step (1) to obtain a mixture, in which 0<x<2;

(3-1) drying the mixture obtained in step (2) to obtain a solid;

(3) mixing the mixture obtained in step (2) or the solid obtained in step (3-1) with a certain mass of sulfur powder, and then performing heat treatment in an inert atmosphere to obtain a negative active material.

2. The method according to claim 1 , wherein in step (1), a ratio of the mass of the polymer to a volume of the solvent is from 0.1 g/L to 10 g/L, optionally from 1 g/L to 5 g /L.

3. The method according to claim 1 , wherein a mass ratio of the SiOx particles in step (2) to the polymer in step (1) is from 10 to 200, and optionally from 20 to 100.

4. The method according to claim 1 , wherein a ratio of the mass of the sulfur powder to the mass of the polymer is (1˜5):1, optionally (2˜4):1.

5. The method according to claim 1 , wherein a heat-treatment temperature is from 250° C. to 450° C., optionally from 300° C. to 450° C., or from 380° C. to 430° C.

6. The method according to claim 1 , wherein a heat treatment time is for 2-8 hours, optionally 3-5 hours.

7. A negative active material obtained by the method according to claim 1 , wherein the negative active material comprises SiO x particles and a modified polymer coating layer covering the SiO x particles, in which 0<x<2;

wherein the negative active material has a peak intensity I 1 at the Raman shift ranging from 280 cm −1 to 345 cm −1 , a peak intensity I 2 at the Raman shift ranging from 450 cm −1 to 530 cm −1 , and a peak intensity I 3 at the Raman shift ranging from 900 cm −1 to 960 cm −1 , and I 1 , I 2 and I 3 satisfy 0.1≤I 1 /I 2 ≤0.6, and 0.2≤I 3 /I 2 ≤1.0.

8. The negative active material according to claim 7 , wherein 0.15≤I 1 /I 2 ≤0.4.

9. The negative active material according to claim 7 , wherein 0.3≤I 3 /I 2 ≤0.8.

10. The negative active material according to claim 7 , wherein the negative active material has a peak intensity I D at the Raman shift ranging from 1300 cm −1 to 1380 cm −1 and a peak intensity I G at the Raman shift ranging from 1520 cm −1 to 1590 cm −1 , and the peak intensity I D and the peak intensity I G satisfy 1.05≤I D /I G ≤1.50; optionally, 1.1≤I D /I G ≤1.45.

11. The negative active material according to claim 7 , wherein a full width at half maxima of the negative active material at the Raman shifts of 1300 cm −1 ˜1380 cm −1 is from 120 cm −1 to 160 cm −1 , optionally from 128 cm −1 to 152 cm −1 .

12. The negative active material according to claim 7 , wherein the modified polymer coating layer comprises sulfur element and carbon element.

13. The negative active material according to claim 12 , wherein a mass percentage of the sulfur element is from 0.5% to 3% of the mass of the negative active material, optionally from 0.8% to 1.5%; and/or,

a mass percentage of the carbon element is from 0.1% to 4% of the mass of the negative active material, optionally from 0.5% to 3%.

14. The negative active material according to claim 7 , wherein the negative active material has an X-ray diffraction pattern comprising a diffraction peak at the diffraction angle 2 θ of 19° to 27° and the diffraction peak has a full width at half maxima of 4° to 12°, and optionally 5° to 10°.

15. The negative active material according to claim 7 , wherein the negative active material has a volume average particle diameter Dv50 of 2 μm-12 μm, optionally 4 μm-8 μm.

16. The negative active material according to claim 7 , wherein the negative active material has a volume particle size distribution Dv10, a volume average particle size Dv50, and a volume particle size distribution Dv90 satisfying: 0.5≤(Dv90−Dv10)/Dv50≤2.5; optionally, 0.8≤(Dv90−Dv10)/Dv50≤2.0.

17. The negative active material according to claim 7 , wherein the negative active material has a specific surface area of 0.5 m 2 /g to 5 m 2 /g, optionally 0.8 m 2 /g-3 m 2 /g.

18. The negative active material according to claim 7 , wherein the negative active material has a tap density of 0.8 g/cm 3 to 1.3 g/cm 3 , optionally 0.9 g/cm 3 to 1.2 g/cm 3 .

19. The negative active material according to claim 7 , wherein the negative active material has a compacted density of 1.1 g/cm 3 to 1.6 g/cm 3 measured under a pressure of 5 tons (equivalent to 49 KN), optionally 1.2 g/cm 3 to 1.5 g/cm 3 .

20. A secondary battery comprising the negative active material according to claim 7 .