Electrolytes for stable cycling of high capacity lithium based batteries
Electrolytes are described with additives that provide good shelf life with improved cycling stability properties. The electrolytes can provide appropriate high voltage stability for high capacity positive electrode active materials. The core electrolyte generally can comprise from about 1.1M to about 2.5M lithium electrolyte salt and a solvent that consists essentially of fluoroethylene carbonate and/or ethylene carbonate, dimethyl carbonate and optionally no more than about 40 volume percent methyl ethyl carbonate, and wherein the lithium electrolyte salt is selected from the group consisting of LiPF 6 , LiBF 4 and combinations thereof. Desirable stabilizing additives include, for example, dimethyl methylphosphonate, thiophene or thiophene derivatives, and/or LiF with an anion complexing agent.
1. An electrolyte composition comprising solvent, from about 1.1M to about 2.5M lithium electrolyte salt, from about 0.001 weight percent to about 0.4 weight percent LiF and an anion complexing agent in an amount by moles from about 0.25 to about 2 times the molar amount of LiF, wherein the solvent consists essentially of fluoroethylene carbonate and/or ethylene carbonate, dimethyl carbonate and optionally methyl ethyl carbonate, and wherein the lithium electrolyte salt is selected from the group consisting of LiPF 6 , LiBF 4 and combinations thereof.
2. The electrolyte composition of claim 1 comprising from about 0.0025 to about 0.25 weight percent LiF.
3. The electrolyte composition of claim 1 wherein the anion complexing agent is tris(1,1,1,3,3,3-hexafluoro-propan-2-yl)borate, tris(1,1,1,3,3,3-hexafluoro-2-phenyl-propan-2-yl)borate, tris(1,1,1,3,3,3-hexafluoro-2-(trifluoromethyl)propan-2-yl)borate, triphenyl borate, tris(4-fluorophenyl)borate, tris(2,4-difluorophenyl)borate, tris(2,3,5,6-tetrafluorophenyl)borate, tris(pentafluorophenyl)borate, tris(3-trifluoromethylphenyl)borate, tris(3,5-bis(trifluoromethyl)phenyl)borate, tris(pentafluorophenyl)borane, 2-(2,4-difluorophenyl)-4-fluoro-1,3,2-benzodioxaborole, 2-(3-trifluoromethylphenyl)-4-fluoro-1,3,2-benzodioxaborole, 2,5-bis(trifluoromethyl)phenyl-4-fluoro-1,3,2-benzodioxaborole, 2-(4-fluorophenyl)-tetrafluoro-1,3,2-benzodioxaborole, 2-(2,4-difluorophenyl)-tetrafluoro-1,3,2-benzodioxaborole, 2-(pentafluorophenyl)-tetrafluoro-1,3,2-benzodioxaborole, 2-(2-trifluoromethyl)phenyl-tetrafluoro-1,3,2-benzodioxaborole, 2,5-bis(trifluoromethyl)phenyl-tetrafluoro-1,3,2-benzodioxaborole, 2-phenyl-4,4,5,5-tetrakis(trifluoromethyl)-1,3,2-benzodioxaborolane, 2-(3,5-difluorophenyl)-4,4,5,5-tetrakis(trifluoromethyl)-1,3,2-dioxaborolane, 2-pentafluorophenyl-4,4,5,5-tetrakis(trifluoromethyl)-1,3,2-dioxaborolane, bis(1,1,1,3,3,3-hexafluoroisopropyl)phenylboronate, bis(1,1,1,3,3,3-hexafluoroisopropyl)-3,5-difluorophenylboronate, bis(1,1,1,3,3,3-hexafluoroisopropyl)(pentafluorophenyl)boronate, or a mixture of any two or more thereof.
4. The electrolyte composition of claim 1 wherein the anion complexing agent is tris(pentafluorophenyl)borane, pentafluorophenylboron oxalate, tris(2H-hexafluoroisopropyl) borate, 2-(pentafluorophenyl)-tetrafluoro-1,3,2-benzodioxaborole, 2-(pentafluorophenyl)-4,4,5,5-tetrakis(trifluoromethyl)-1,3,2-dioxaborolane, and combinations thereof.
5. The electrolyte composition of claim 1 comprising from about 0.025 weight percent to about 0.1 weight percent LiF and anion complexing agent in an amount by moles from about 0.5 to about 1.25 times the molar amount of LiF.
6. The electrolyte composition of claim 1 wherein the electrolyte comprises from about 1.15M to about 1.6M lithium electrolyte salt.
7. The electrolyte composition of claim 1 further comprising from about 0.1 weight percent to about 5 weight percent LiBOB, LiDFOB or a combination thereof.
8. The electrolyte composition of claim 1 further comprising from about 1 to about 5 weight percent LiBOB, LiDFOB or a combination thereof.
9. The electrolyte composition of claim 1 wherein the solvent consists essentially of ethylene carbonate and dimethyl carbonate at a weight ratio from about 1:1 to about 1:4 and methyl ethyl carbonate at a concentration relative to the total electrolyte weight from 0 to about 30 weight percent.
10. The electrolyte composition of claim 1 wherein the solvent consists essentially of fluoroethylene carbonate and dimethyl carbonate at a weight ratio from about 1:1 to about 1:4.
11. The electrolyte composition of claim 1 wherein the solvent comprises no more than about 40 volume percent methyl ethyl carbonate.
12. The electrolyte composition of claim 1 wherein the solvent consists essentially of fluoroethylene carbonate, dimethyl carbonate and methyl ethyl carbonate.
13. The electrolyte composition of claim 12 wherein the solvent comprises no more than about 40 volume percent methyl ethyl carbonate.
14. The electrolyte composition of claim 1 further comprising from about 0.01 to about 0.4 weight percent dimethyl methylphosphonate.
15. A lithium ion battery comprising a positive electrode, a negative electrode, a separator separating the positive electrode, and an electrolyte of claim 1 , wherein the positive electrode comprises an active material comprising a lithium rich metal oxide,
wherein the positive electrode active material has a specific capacity of at least about 140 mAh/g at a 1C rate discharged from 4.35V to 2V and wherein the battery has a capacity at the 500th cycle that is at least about 97.5% of the 5th cycle capacity when cycled at a discharge rate of 1C from 4.35V to 2.5V.
16. The lithium ion battery of claim 15 wherein the negative electrode comprises graphitic carbon.
17. The lithium ion battery of claim 15 wherein the negative electrode comprises a silicon based active material.