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The present invention relates to an improvement in lithium secondary batteries comprised of a negative electrode, a positive electrode, a separator, and a lithium-based electrolyte carried in an aprotic solvent and to the electrolyte compositions. The improvement resides in the use of a lithium salt

The present invention relates to an improvement in lithium secondary batteries comprised of a negative electrode, a positive electrode, a separator, and a lithium-based electrolyte carried in an aprotic solvent and to the electrolyte compositions. The improvement resides in the use of a lithium salt of the formula: description="In-line Formulae" end="lead"Li2B12FxZ12-x description="In-line Formulae" end="tail" wherein x greater than or equal to 4 and Z represents H, Cl, and Br.

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The invention claimed is: 1. A secondary battery comprising: a positive electrode, a negative electrode, an organic solvent comprising at least one carbonate, a lithium salt of the formula: description="In-line Formulae" end="lead"Li2B12FxZ12-x description="In-line Formulae" end="tail" where x

The invention claimed is: 1. A secondary battery comprising: a positive electrode, a negative electrode, an organic solvent comprising at least one carbonate, a lithium salt of the formula: description="In-line Formulae" end="lead"Li2B12FxZ12-x description="In-line Formulae" end="tail" where x is greater than or equal to 8 and less than or equal to 12 and Z is Cl, or Br; and at least one member selected from the group consisting of LiPF6, lithium per chlorate, lithium hexafluoroaresenate, lithium tetrafluoroborate and lithium hexafluroantimonate. 2. The battery of claim 1 wherein x is 12. 3. The battery of claim 1 wherein x is less than 12 and Z is Cl, or Br. 4. The battery of claim 1 wherein the lithium salt is selected from the group consisting of Li2B12F8H4, Li2B12F9H3, Li2B12F10H2, Li2B12F11H. 5. The battery of claim 2 wherein the concentration of said lithium salt in said solvent is from 0.01 to 1 molar. 6. The battery of claim 1 wherein said lithium salt is selected from the group consisting of Li2B12FxCl12-x and Li2B12FxBr12-x where x is 10 or 11. 7. The battery of claim 1 wherein said solvent is selected from the group consisting of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl trifluoroethyl carbonate, dimethoxyethane, diglyme, and triglyme, propylene carbonate, trifluoropropylene carbonate, chloroethylene carbonate, vinylene carbonate, butylene carbonate, dimethylvinylene carbonate, and aprotic gel polymers. 8. The battery of claim 1 wherein x is 10 and at least one Z is Cl. 9. The battery of claim 7 wherein x is 10 or 11 and Z is Cl or Br. 10. The battery of claim 1 wherein the positive electrode comprises at least one oxide. 11. The battery of claim 1 wherein the negative electrode comprises at least one member selected from the group consisting of carbon, tin oxide, silicon and germanium compounds. 12. The battery of claim 1 wherein the battery retains at least 75% of its charge capacity after being maintained at a temperature of 85 C for 72 hours. 13. An electrolyte for a secondary lithium battery comprising a first lithium salt, and at least one carbonate solvent, said first lithium salt comprising: description="In-line Formulae" end="lead"Li2B12FxZ12-x description="In-line Formulae" end="tail" wherein x is at least 10 but not more than 12 and Z is H, Cl, or Br, and at least one other lithium based salt. 14. The lithium electrolyte of claim 13 wherein x is at least 11. 15. The lithium electrolyte of claim 13 wherein the solvent is selected from the group consisting of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl trifluoroethyl carbonate, dimethoxyethane, diglyme, and triglyme, propylene carbonate, trifluoropropylene carbonate, chloroethylene carbonate, vinylene carbonate, butylene carbonate, dimethylvinylene carbonate, and an aprotic gel polymer, or polymer matrix. 16. The lithium electrolyte of claim 13 wherein the solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate. 17. The lithium electrolyte of claim 13 wherein x is 10 or 11 and Z is Cl or Br. 18. The lithium electrolyte of claim 13 wherein x is 12. 19. The lithium electrolyte of claim 13 wherein said first lithium salt is selected from the group consisting of Li2B12F10H2, and Li2B12F11H. 20. The lithium electrolyte of claim 13 wherein said at least one other lithium based salt comprises at least one member selected from the group consisting of LiPF6, lithium per chlorate, lithium hexafluoroaresenate, lithium tetrafluoroborate and lithium hexafluroantimonate. 21. The lithium electrolyte of claim 20 wherein said at least one member comprises LiPF6. 22. The electrolyte of claim 13 wherein said electrolyte has a conductivity of greater than about 4 mS/cm. 23. The electrolyte of claim 15 wherein the solvent comprises vinylene carbonate. 24. A secondary battery comprising: a positive electrode comprising at least one oxide, a negative electrode, an organic solvent comprising at least one carbonate, a first lithium salt of the formula: description="In-line Formulae" end="lead"Li2B12FxZ12-x description="In-line Formulae" end="tail" where x is greater than or equal to 10 and less than or equal to 12 and Z is H, Cl, or Br; and at least one other lithium based salt. 25. The battery of claim 24 wherein the positive electrode comprises a lithium composite oxide. 26. The battery of claim 24 wherein the lithium composite oxide comprises lithium manganese spinel. 27. The battery of claim 26 wherein the negative electrode comprises carbon.