Li

1. A method of preparing graphene-wrapped Li 2 S nanoparticles, the method comprising:

heating lithium metal and a carbon-sulfur source or lithium metal, a carbon source, and a sulfur source in a sealed container at a temperature to produce lithium vapors and vapors of the carbon-sulfur source, or lithium vapors, vapors of the carbon source, and vapors of the sulfur source; and

cooling the sealed container to produce the graphene-wrapped Li 2 S nanoparticles.

2. The method of claim 1 , wherein the temperature is about 180° C. to about 800° C.

3. The method of claim 1 , wherein the method comprises heating lithium metal and a carbon-sulfur source.

4. The method of claim 3 , wherein the carbon-sulfur source is CS 2 .

5. The method of claim 1 , wherein the graphene-wrapped Li 2 S nanoparticles have a Li 2 S loading of about 1 mg/cm 2 to about 15 mg/cm 2 .

6. The method of claim 1 , wherein the graphene-wrapped Li 2 S nanoparticles comprise Li 2 S nanoparticles encapsulated by graphene nanocages.

7. The method of claim 6 , wherein the graphene nanocages are about 50 nm to 100 nm wide.

8. The method of claim 6 , wherein the Li 2 S nanoparticles are uniformly distributed among and within the graphene nanocages.

9. The method of claim 6 , wherein the graphene nanocages comprise at least 5 graphene layers.

10. Graphene-wrapped Li 2 S nanoparticles prepared by the method of claim 1 .

11. A cathode comprising the graphene-wrapped Li 2 S nanoparticles of claim 10 .

12. The cathode of claim 11 , further comprising a current collector, a conductive carbon material, a binder, or any combination thereof.