Additives for high voltage lithium ion batteries
This invention relates to a method for preparing an electrochemical cell comprising the sequential steps of preparing a solution of a lithium salt in an non-aqueous solvent containing an additive compound, and maintaining the solution at a temperature in the range of about 20 to about 30° C. for about 5 to 10 days to form an aged electrolyte; assembling an electrochemical cell from an anode, a cathode, and the aged electrolyte; and electrochemically subjecting the electrochemical cell to formation cycling. The additive compound comprises one or more compounds selected from the group consisting of: (R 3 SiO) 3 B, (R 3 SiO) 3 XY, (R 3 SiO) 3 P, (R′O) 3 PO, (R 3 Si) 3 X′, R 3 SiOS(O) 2 R′; (R 3 Si)OC(═O)R′; wherein each R and R′ independently is a hydrocarbyl group; X is P or B; Y is O or S; X is Ti or Al. Electrochemical cells and batteries also are described.
1. A method for preparing an electrochemical cell; the method comprising the sequential steps of:
(a) preparing a solution of a lithium salt in a non-aqueous solvent containing an additive compound, and maintaining the solution at a temperature in the range of about 20 to about 30° C. for about 5 to 10 days to form an aged electrolyte; wherein the lithium salt is present in the solution at a concentration in the range of about 0.1 molar (M) to about 3 M and the additive compound is present in the solution at a concentration in the range of about 0.0005 M to about 0.2 M;
(b) assembling an electrochemical cell by contacting an anode and a cathode with the aged electrolyte;
(c) electrochemically subjecting the electrochemical cell to formation cycling to form a solid electrolyte interface (SEI) on the anode thereof;
wherein the additive compound comprises one or more compounds selected from the group consisting of: (R 3 SiO) 3 B, (R 3 SiO) 3 XY, (R 3 SiO) 3 P, (R′O) 3 PO, (R 3 Si) 3 X′, R 3 SiOS(O) 2 R′; (R 3 Si)OC(═O)R; wherein each R and R′ independently is a hydrocarbyl group; X is P or B; Y is O or S; X′ is Ti or Al.
2. The method of claim 1 , wherein each R and R′ independently is a hydrocarbyl moiety selected from the group consisting of alkyl, aryl, aryl-substituted alkyl and alkyl-substituted aryl.
3. The method of claim 1 , wherein the additive compound comprises a compound of formula (R 3 SiO) 3 P, wherein each R independently is a hydrocarbyl group.
4. The method of claim 3 , wherein each R independently is a hydrocarbyl moiety selected from the group consisting of alkyl, aryl, aryl-substituted alkyl and alkyl-substituted aryl.
5. The method of claim 3 , wherein each R independently is a hydrocarbyl moiety selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl, and phenyl.
6. The method of claim 3 , wherein each R is methyl.
7. The method of claim 3 , wherein step (a) produces a compound of formula R 3 SiOP(O) n F 2 from the additive compound; wherein each R independently is a hydrocarbyl group; and n is 0 or 1; wherein the additive is substantially free from (R 3 SiO) 3 P(O) n and (R 3 SiO) 2 P(O) n F.
8. The method of claim 7 , wherein each R independently is a hydrocarbyl moiety selected from the group consisting of alkyl, aryl, aryl-substituted alkyl and alkyl-substituted aryl.
9. The method of claim 7 , wherein each R independently is a hydrocarbyl moiety selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl, and phenyl.
10. The method of claim 7 , wherein each R is methyl.
11. The method of claim 3 , wherein the lithium salt comprises at least on salt selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imidate (LiTFSI), lithium 2-trifluoromethyl-4,5-dicyanoimidazolate (LiTDI), lithium 4,5-dicyano-1,2,3-triazolate (LiDCTA), lithium trifluoromethanesulfonate (LiTf), lithium perchlorate (LiClO 4 ), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoroborate (LiBF 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium thiocyanate (LiSCN), lithium bis(fluorosulfonyl)imidate (LiFSI), lithium bis(pentafluoroethylsulfonyl)imidate (LBETI), lithium tetracyanoborate (LiB(CN) 4 ), and lithium nitrate.
12. The method claim 3 , wherein the lithium salt comprises LiPF 6 .
13. The method of claim 3 , wherein the non-aqueous solvent comprises at least one solvent selected from the group consisting of an ether, a carbonate ester, a nitrile, a sulfoxide, a sulfone, a fluoro-substituted linear dialkyl carbonate, a fluoro-substituted cyclic alkylene carbonate, a fluoro-substituted sulfolane, and a fluoro-substituted sulfone.
14. The method of claim 3 , wherein the non-aqueous solvent comprises a combination of an alkylene carbonate and a dialkyl carbonate.