Method of preparing negative active material for rechargeable lithium battery, and negative active material and rechargeable lithium battery prepared from the same

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

preparing a solution including spherically shaped natural graphite particles and a solvent;

ultrasonic wave-treating the solution;

drying the ultrasonic wave-treated solution to prepare graphite modified particles; and

heat-treating the graphite modified particles to prepare graphite modified composite particles after preparing the graphite modified particles,

wherein the spherically shaped natural graphite particles are prepared by assembling flake-shaped natural graphite particles into a spherical shape, and

wherein ultrasonic waves are radiated at an intensity of about 100 to about 1000 W for about 1 to about 10 minutes.

2. The method of claim 1 , wherein the spherically shaped natural graphite particles have an average particle diameter (D50) of about 3 to about 40 μm.

3. The method of claim 1 , wherein the solvent comprises at least one selected from water, N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methylethylketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, and ethyl acetate.

4. The method of claim 1 , wherein the spherically shaped natural graphite particles are included in an amount of about 0.1 to about 200 parts by weight based on 100 parts by weight of the solvent.

5. The method of claim 1 , wherein the ultrasonic waves have a frequency of about 10 to about 40 kHz.

6. The method of claim 1 , wherein the drying is performed using at least one spray dry method selected from rotary spray, nozzle spray, and ultrasonic wave spray methods; a drying method using a rotary evaporator; a vacuum-dry method; or a natural drying method.

7. The method of claim 1 , wherein the solution further comprises a carbon precursor, and the carbon precursor comprises at least one selected from citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxylmethyl cellulose (CMC), hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, a phenolic resin, a furan resin, furfuryl alcohol, polyacrylic acid, sodium polyacrylate, polyacrylonitrile, polyimide, an epoxy resin, cellulose, styrene, polyvinyl alcohol, polyvinylchloride, coal-based pitch, petroleum-based pitch, mesophase pitch, low molecular weight heavy oil, glucose, gelatin, and saccharides.

8. The method of claim 1 , wherein the heat-treating is performed at a temperature of about 500 to about 2500° C.

9. The method of claim 1 , wherein the heat-treating is performed under an atmosphere including nitrogen, argon, hydrogen, air, oxygen, or a mixed gas thereof, or under vacuum.

10. The method of claim 1 , wherein the solution further comprises a carbon precursor, and the carbon precursor is included in an amount of about 0.1 to about 80 parts by weight based on 100 parts by weight of the spherically shaped natural graphite particles.

11. The method of claim 1 , wherein the solution further comprises a lithium compound, and

the method further comprises heat-treating the graphite modified particles to prepare graphite modified composite particles after preparing the graphite modified particles.

12. The method of claim 11 , wherein the lithium compound comprises at least one selected from lithium hydroxide including LiOH or LiOH.(H 2 O); lithium nitrate (LiNO 3 ); lithium acetate including CH 3 COO.Li or CH 3 COO.Li.2(H 2 O); lithium carbonate (Li 2 CO 3 ); and lithium fluoride (LiF).

13. The method of claim 11 , wherein the heat-treating is performed at a temperature of about 150 to about 2500° C.

14. The method of claim 11 , wherein the lithium compound is included in an amount of about 0.1 to about 50 parts by weight based on 100 parts by weight of the spherically shaped natural graphite particles.