Lithium-sulfur batteries

1. A lithium-sulfur electrochemical cell comprising:

an anode;

a cathode comprising a polytetrafluoroethylene-coated carbon paper and sulfur wherein the sulfur is elemental sulfur embedded in the polytetrafluoroethylene-coated carbon paper; and

an electrolyte consisting essentially of a salt, a non-polar fluorinated ether solvent, and optionally a non-fluorinated co-solvent selected from the group consisting of 1,3-dioxolane (DOL); dimethoxyethane (DME), di(ethylene glycol) dimethyl ether, tri(ethylene glycol) dimethyl ether, tetra(ethylene glycol) dimethyl ether (TEGDME), oligo(ethylene glycol)-substituted siloxanes, oligo(ethylene glycol)-substituted silanes, or ionic liquids.

2. The lithium-sulfur electrochemical cell of claim 1 , wherein the non-polar fluorinated ether solvent is of formula R—O—R 1 , wherein R is a partially fluorinated, or perfluorinated alkyl group, and R 1 is a partially fluorinated, or perfluorinated alkyl group, R and R 1 optionally being interrupted by oxygen atoms, and R and R 1 may join to form a cyclic fluorinated ether.

3. The lithium-sulfur electrochemical cell of claim 1 , wherein the non-polar fluorinated ether solvent comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE); 1,1,2,2-tetrafluoroethyl-2,2,3,3,3-pentafluoropropyl ether; 2,2,2-trisfluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether; ethyl-1,1,2,3,3,3-hexafluoropropyl ether; difluoromethyl-2,2,3,3,3-pentafluoropropyl ether; or difluoromethyl-2,2,3,3-tetrafluoropropyl ether.

4. The lithium-sulfur electrochemical cell of claim 1 , wherein the non-polar fluorinated ether solvent comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE).

5. The lithium-sulfur electrochemical cell of claim 1 , wherein the anode comprises elemental lithium.

6. The lithium-sulfur electrochemical cell of claim 5 , wherein the non-polar fluorinated ether solvent is of formula R—O—R 1 , wherein R is a partially fluorinated, or perfluorinated alkyl group, and R 1 is a partially fluorinated, or perfluorinated alkyl group, R and R 1 optionally being interrupted by oxygen atoms, and R and R 1 may join to form a cyclic fluorinated ether.

7. The lithium-sulfur electrochemical cell of claim 5 , wherein the non-polar fluorinated ether solvent comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE); 1,1,2,2-tetrafluoroethyl-2,2,3,3,3-pentafluoropropyl ether; 2,2,2-trisfluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether; ethyl-1,1,2,3,3,3-hexafluoropropyl ether; difluoromethyl-2,2,3,3,3-pentafluoropropyl ether; difluoromethyl-2,2,3,3-tetrafluoropropyl ether; 2-fluoro-1,3-dioxolane; 2,2-difluoro-1,3-dioxolane; 2-trifluoromethyl-1,3-dioxolane; 2,2-bis(trifluoromethyl)-1,3-dioxolane; 4-fluoro-1,3-dioxolane; or 4,5-difluoro-1,3-dioxolane.

8. The lithium-sulfur electrochemical cell of claim 5 , wherein the non-polar fluorinated ether solvent comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE).

9. The lithium-sulfur electrochemical cell of claim 1 , wherein the non-fluorinated solvent comprises 1,3-dioxolane.

10. The lithium-sulfur electrochemical cell of claim 1 , wherein the salt is present in the electrolyte at a concentration from about 0.1 M to about 3 M.

11. The lithium-sulfur electrochemical cell of claim 1 , wherein the salt comprises a lithium salt.

12. The lithium-sulfur electrochemical cell of claim 11 , wherein the lithium salt comprises LiNO 3 , Li[BF 2 (C 2 O 4 )], LiPF 6 , LiClO 4 , Li(CF 3 SO 2 ) 2 N, LiC(SO 2 CF 3 ) 3 , (Li(C 2 F 5 SO 2 ) 2 N), LiCF 3 SO 3 , Li 2 B 12 X 12−n H n , Li 2 B 10 X 10−n′ H n′ , where X is a halogen, n is an integer from 0 to 12, and n′ is an integer from 0 to 10, LiAlF 4 , LiBF 4 , Li(FSO 2 ) 2 N, Li 2 SO 4 , or LiAsF 6 .

13. The lithium-sulfur electrochemical cell of claim 12 , wherein the LiNO 3 or Li[BF 2 (C 2 O 4 )] is present in the electrolyte at a concentration from about 0.1 M to about 0.4 M.