Method for producing sulfur charged carbon nanotubes and cathodes for lithium ion batteries
A method for making sulfur charged carbon nanotubes, the structure of the sulfur charged carbon nanotubes, and a cathode including the sulfur charged carbon nanotubes are described herein. The method comprises dissolving sublimed sulfur in a solvent to create a solution. The method further comprises adding carbon nanotubes to the solution. The method further comprises adding a polar protic solvent to the solution. The method further comprises removing the solvent from the solution.
1. A method for making sulfur charged carbon nanotubes comprising
dissolving sublimed sulfur in an initial solvent to create a solution;
adding carbon nanotubes to the solution, each having an exterior wall;
adding a polar protic solvent to the solution; and
removing the initial solvent from the solution to form the sulfur charged carbon nanotubes, wherein
a first plurality of sulfur particles is contained within each sulfur charged carbon nanotube; and
a second plurality of sulfur particles is directly pi-bonded to the exterior walls of the sulfur charged carbon nanotubes.
2. The method of claim 1 , wherein the initial solvent comprises carbon disulfide.
3. The method of claim 1 , wherein dissolving the sublimed sulfur in the initial solvent comprises at least one of sonicating the solution, stirring the solution, and heating the solution.
4. The method of claim 1 , wherein removing the initial solvent comprises
evaporating a first portion of the initial solvent by heating the solution; and
removing a second portion of the initial solvent by air drying the solution.
5. The method of claim 1 , wherein adding the carbon nanotubes comprises at least one of sonicating the solution, stirring the solution, and heating the solution.
6. The method of claim 1 , wherein adding the polar protic solvent comprises drop-wise adding the polar protic solvent at a controlled rate.
7. The method of claim 1 , wherein at least a portion of the sublimed sulfur fills the plurality of carbon nanotubes by nanocapillary action.
8. The method of claim 1 , where the addition of the polar protic solvent results in a substantially uniform size distribution of the first and second pluralities of sulfur particles.
9. The method of claim 1 , wherein the step of dissolving sublimed sulfur in the initial solvent occurs at a temperature of 32° C. to 33° C.
10. The method of claim 1 , wherein the sublimed sulfur is about 50 to 98 percent of the final combined sulfur-nanotube mixture by weight.
11. The method of claim 1 , wherein the carbon nanotubes are about 2 to 50 percent by weight of a combined mixture of the initial solution and the carbon nanotubes.
12. The method of claim 1 , wherein the carbon nanotubes are double walled carbon nanotubes.
13. The method of claim 1 , wherein the carbon nanotubes are less than about 5 micrometers in length.
14. The method of claim 5 , wherein the solution is heated to 32° C. to 33° C.