Negative electrode active material, method of preparing the same, and negative electrode and lithium secondary battery which include the negative electrode active material

1. A negative electrode active material comprising a silicon-based composite and a carbon-based material,

wherein the silicon-based composite comprises:

SiO x (0≤x≤2) including pores;

a polymer disposed in the pores; and

a metal compound disposed on a surface of the SiOx or on the surface and interior of the SiO x ,

wherein the metal compound comprises at least one element selected from the group consisting of lithium (Li), magnesium (Mg), calcium (Ca), and aluminum (Al),

the polymer comprises polyacrylate, and

the silicon-based composite has a Brunauer-Emmett-Teller (BET) specific surface area of 0.5 m 2 /g to 2.5 m 2 /g.

2. The negative electrode active material of claim 1 , wherein a ratio of the silicon-based composite to the carbon-based material is 1:99 to 50:50.

3. The negative electrode active material of claim 1 , wherein the carbon-based material comprises at least one selected from the group consisting of natural graphite, artificial graphite, graphitizable carbon, non-graphitizable carbon, carbon black, and graphite oxide.

4. The negative electrode active material of claim 1 , wherein the SiO x has a plurality of pores having a diameter of 50 nm to 1,000 nm.

5. The negative electrode active material of claim 1 , wherein the metal compound comprises at least one metal silicate selected from the group consisting of Li 2 Si 2 O 5 , Li 2 SiO 3 , Li 4 SiO 4 , Mg 2 SiO 4 , CaSiO 3 , 3Al 2 O 3 ·2SiO 2 , and MgSiO 3 .

6. The negative electrode active material of claim 1 , wherein the metal compound is included in an amount of 1 wt % to 30 wt % based on a total weight of the silicon-based composite.

7. The negative electrode active material of claim 1 , wherein the polymer further comprises polyacrylic acid.

8. The negative electrode active material of claim 1 , wherein the silicon-based composite further comprises a carbon coating layer disposed on the silicon-based composite.

9. The negative electrode active material of claim 1 , wherein the silicon-based composite has an average particle diameter (D 50 ) of 1 μm to 20 μm.

10. A method of preparing the negative electrode active material according to claim 1 , the method comprising:

mixing SiO x (0≤x≤2) with at least one element selected from the group consisting of lithium (Li), magnesium (Mg), calcium (Ca), and aluminum (Al) and performing a first heat treatment to dispose a metal compound on a surface of the SiO x or on the surface and interior of the SiO x ;

immersing the first heat-treated SiO x in an etching solution to form pores in the SiO x ;

mixing the SiO x having the pores formed therein with a polymer and performing a second heat treatment to form a silicon-based composite by disposing the polymer in the pores; and

mixing the silicon-based composite and a carbon-based material,

wherein the polymer comprises polyacrylate.

11. The method of claim 10 , wherein the first heat treatment is performed at 400° C. to 1,200° C. for 1 hour to 5 hours.

12. The method of claim 10 , wherein the etching solution comprises at least one selected from sodium hydroxide (NaOH) and potassium hydroxide (KOH).

13. The method of claim 10 , wherein the polymer further comprises polyacrylic acid.

14. The method of claim 10 , wherein the second heat treatment is performed at 200° C. to 500° C. for 1 hour to 5 hours.

15. The method of claim 10 , further comprising forming a carbon coating layer on the SiO x before the first heat treatment, after the first heat treatment, or after the formation of the pores in the SiO x .

16. A negative electrode comprising the negative electrode active material of claim 1 .

17. A secondary battery comprising:

the negative electrode of claim 16 ;

a positive electrode;

a separator disposed between the positive electrode and the negative electrode; and

an electrolyte.

18. The negative electrode active material of claim 1 , wherein the metal compound comprises at least one metal silicate selected from the group consisting of Mg 2 SiO 4 and MgSiO 3 .

19. The method of claim 10 , wherein the second heat treatment is performed at 300° C. to 400° C. for 2 hours to 3 hours.