Negative electrode active material, negative electrode including the same and lithium secondary battery including the same

1. A negative electrode active material comprising:

secondary particles having a plurality of primary particles comprising a silicon oxide composite including

i) Si,

ii) a silicon oxide represented by SiO x (0<x≤2), and

iii) a metal silicate containing Si and a metal (M), wherein M comprises at least one of Li or Mg; and

a first carbon coating layer disposed partially or totally on the surfaces of the primary particles to interconnect and fix the primary particles; and

a second carbon coating layer disposed on an entire outer surfaces of the secondary particles,

wherein the second carbon coating layer has higher crystallinity as compared to the first carbon coating layer, and

the primary particles have an average particle diameter (D 50 ) of 0.1-3.5 μm.

2. The negative electrode active material according to claim 1 , wherein a full width at half-maximum (FWHM) value of a D band in Raman spectroscopy of the first carbon coating layer is at least 1.3 times larger than the FWHM value of a D band in Raman spectroscopy of the second carbon coating layer.

3. The negative electrode active material according to claim 1 , wherein an average particle diameter (D 50 ) of the negative electrode active material is 5-15 μm.

4. A method for preparing a negative electrode active material according to claim 1 , comprising the steps of:

preparing a plurality of primary particles which include comprising a silicon oxide composite including i) Si, ii) a silicon oxide represented by SiO x (0<x≤2), and iii) a metal silicate containing Si and a metal (M), wherein M comprises at least one of Li or Mg;

mixing and firing the primary particles with a first carbonaceous material to prepare secondary particles having a first carbon coating layer disposed partially or totally on the surfaces of the primary particles to interconnect and fix the primary particles; and

injecting a second carbonaceous material gas into the secondary particles and carrying out heat treatment at 850-1,150° C. for 30 minutes to 8 hours to form a second carbon coating layer surrounding the secondary particles.

5. The method for preparing a negative electrode active material according to claim 4 , wherein the step of preparing a plurality of primary particles comprises:

carrying out a reaction of SiO x (0<x<2) gas with at least one metal gas selected from Li and Mg, and cooling a reaction mixture at 400-900° C. to deposit a silicon oxide composite; and

pulverizing the deposited silicon oxide composite.

6. The method for preparing a negative electrode active material according to claim 5 , wherein the SiO x (0<x<2) gas is prepared by allowing Si and SiO 2 to evaporate at 1,000-1,800° C., and the metal gas is prepared by allowing at least one metal selected from Li and Mg to evaporate at 800-1,600° C.

7. The method for preparing a negative electrode active material according to claim 4 , wherein the step of mixing and firing the primary particles with the first carbonaceous material comprises the steps of:

mixing the primary particles with the first carbonaceous material to form secondary particle shapes and carrying out a low-temperature heat treatment at 600-700° C. for 2-6 hours; and

carbonizing a low-temperature heat treated product under a nitrogen atmosphere at a temperature of 900-1,200° C. for 0.5-8 hours.

8. A negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer comprising the negative electrode active material according to claim 1 , disposed on at least one surface of the negative electrode current collector.

9. A lithium secondary battery comprising the negative electrode according to claim 8 .

10. The negative electrode active material according to claim 1 , wherein the primary particles comprise a plurality of silicon phases comprising crystalline silicon and a matrix comprising the silicon oxide composite.

11. The negative electrode active material according to claim 10 , wherein a crystallite size of the silicon phase is 15 nm or less.

12. The negative electrode active material according to claim 2 , wherein the D band is a band appearing at about 1360 cm −1 , which is a peak representing sp 3 binding of the carbon coating layers.

13. The negative electrode active material according to claim 2 , wherein the FWHM value of the D band of the first carbon coating layer is a 1.3-3 times larger than the FWHM value of the D band of the second carbon coating layer.

14. The negative electrode active material according to claim 2 , wherein the FWHM value of the D band of the first carbon coating layer is a 1.3-2 times larger than the FWHM value of the D band of the second carbon coating layer.

15. The negative electrode active material according to claim 1 , wherein a content of the first carbon coating layer is 3-15 parts by weight based on 100 parts by weight of the primary particles.

16. The negative electrode active material according to claim 1 , wherein a content of the first carbon coating layer is 3-10 parts by weight based on 100 parts by weight of the primary particles.

17. The negative electrode active material according to claim 1 , wherein a content of the first carbon coating layer is 3-8 parts by weight based on 100 parts by weight of the primary particles.

18. The negative electrode active material according to claim 1 , wherein the metal (M) is present in an amount of 3-20 wt % based on 100 wt % of the silicon oxide composite.

19. The negative electrode active material according to claim 1 , wherein the metal (M) is present in an amount of 4-15 wt % based on 100 wt % of the silicon oxide composite.

20. The negative electrode active material according to claim 1 , wherein a 50% particle diameter (D50) of the primary particles is 0.1-3.5 μm.