Method of preparing negative active material containing a carbon-coated silicon core for a rechargeable lithium battery and a rechargeable lithium battery

1. A method of preparing a negative active material for a rechargeable lithium battery comprising the steps of:

a) mixing a silicon precursor of silicon halide, a surfactant comprising an ammonium halide salt having an organic group, an initiator, and a solvent;

b) heat-treating the mixture to form a reverse micelle structure in which silicon particles are surrounded by the surfactant;

c) cooling the heat-treated mixture to room temperature;

d) washing the cooled, heat-treated mixture; and

e) calcining the washed product,

wherein the negative active material for the rechargeable lithium battery has a particle diameter of 3 nm to 30 nm,

wherein the negative active material for the rechargeable lithium battery comprises a core comprising silicon;

wherein the surfactant is degraded by the calcination; and

wherein carbon atoms derived from the calcined surfactant form a coating layer on the surface of the core.

2. The method according to claim 1 , wherein the ammonium halide salt is represented by the following Chemical Formula 1:

wherein,

R 1 , R 2 , R 3 , and R 4 are the same or different from each other, and independently represent hydrogen, or a C 1 -C 30 aliphatic organic group, and

X is F, Cl, Br, or I.

3. The method according to claim 1 , wherein the mixture comprises 50 to 70 weight % of the silicon precursor, to 20 weight % of the surfactant, 10 to 45 weight % of the initiator, and the remaining weight % of the solvent.

4. The method according to claim 1 , wherein the initiator is sodium naphthalide.

5. The method according to claim 1 , wherein the solvent is hexane, isopropyl alcohol, or a mixture thereof.

6. The method according to claim 1 , wherein the heat-treatment is carried out at the temperature of 300° C. to 500° C.

7. The method according to claim 1 , wherein the washing process is carried out by using hexane, water, or a mixture thereof.

8. The method according to claim 1 , wherein the calcination step is carried out at a temperature of 600° C. to 1000° C.

9. The method according to claim 1 , further comprising the step of coating the surface of the calcined product with carbon.

10. The method according to claim 1 , wherein the particle diameter has a deviation of 2 nm or less.

11. The method according to claim 1 , wherein the silicon in the core is crystalline and the carbon in the coating layer is amorphous.

12. The method according to claim 1 , wherein the coating layer has a thickness of 0.5 nm to 5 nm.

13. The method according to claim 1 , wherein the negative active material for the rechargeable lithium battery has a dispersity of 70 to 95%.