Lithium-ion electrolytes containing flame retardant additives for increased safety characteristics
The invention discloses various embodiments of Li-ion electrolytes containing flame retardant additives that have delivered good performance over a wide temperature range, good cycle life characteristics, and improved safety characteristics, namely, reduced flammability. In one embodiment of the invention there is provided an electrolyte for use in a lithium-ion electrochemical cell, the electrolyte comprising a mixture of an ethylene carbonate (EC), an ethyl methyl carbonate (EMC), a fluorinated co-solvent, a flame retardant additive, and a lithium salt. In another embodiment of the invention there is provided an electrolyte for use in a lithium-ion electrochemical cell, the electrolyte comprising a mixture of an ethylene carbonate (EC), an ethyl methyl carbonate (EMC), a flame retardant additive, a solid electrolyte interface (SEI) film forming agent, and a lithium salt.
1. An electrolyte for use in a lithium-ion electrochemical cell, the electrolyte comprising a mixture of:
an ethylene carbonate (EC);
an ethyl methyl carbonate (EMC);
a fluorinated co-solvent selected from a group consisting of fluorinated carbonates, fluorinated ester co-solvents, and fluorinated ethers;
a flame retardant additive selected from a group consisting of fluorinated phosphate flame retardant additives, phosphite flame retardant additives, and phosphonate flame retardant additives; and,
a lithium salt
wherein the electrolyte comprises from about 5% to about 30% by volume flame retardant additive.
2. The electrolyte of claim 1 wherein the fluorinated co-solvent is selected from the group consisting of 2,2,2-trifluoroethyl butyrate (TFEB), di-2,2,2-trifluoroethyl carbonate (DTFEC), 2,2,2-trifluoroethyl methyl carbonate (TFEMC), mono-fluoroethylene carbonate (FEC), ethyl trifluoroacetate (ETFA), 2,2,2-trifluoroethyl acetate (TFEA), 2,2,2-trifluoroethyl propionate (TFEP), ethyl-2,2,2-trifluoroethyl carbonate (ETFEC), propyl-2,2,2-trifluoroethyl carbonate (PTFEC), methyl-2,2,2,2′,2′,2′-hexafluoro-i-propyl carbonate (MHFPC), ethyl-2,2,2,2′,2′,2′-hexafluoro-i-propyl carbonate (EHFPC), fluoropropylene carbonate (FPC), trifluoropropylene carbonate (TFPC), methyl nonafluorobutyl ether, 2,2,3,3,3-pentafluoropropyl methyl ether, 1,1,3,3,3-pentafluoro-2-trifluoromethyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, and perfluoropolyether.
3. The electrolyte of claim 1 wherein the flame retardant additive is selected from the group consisting of bis(2,2,2-trifluoroethyl) methyl phosphonate (BTFEMP/TFMPo), triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, tris(2,2,2-trifluoroethyl) phosphite, diethyl ethylphosphonate, and diethyl phenylphosphonate.
4. The electrolyte of claim 1 wherein the lithium salt is selected from the group consisting of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium bis(oxalate) borate (LiBOB), lithium hexafluoroarensate (LiAsF 6 ), lithium perchlorate (LiClO 4 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bistrifluoromethanesulfonate sulfonyl imide (LiN(SO 2 CF 3 ) 2 ), and mixtures thereof.
5. The electrolyte of claim 1 wherein the electrolyte comprises from about 10% to about 60% by volume fluorinated co-solvent.
6. The electrolyte of claim 1 wherein the electrolyte comprises from about 5% to about 15% by volume flame retardant additive.
7. The electrolyte of claim 1 wherein the electrolyte comprises 1.0 M LiPF 6 in 20% by volume ethylene carbonate (EC) plus 55% by volume ethyl methyl carbonate (EMC) plus 20% by volume 2,2,2-tri-fluoroethyl butyrate (TFEB) plus 5% by volume triphenyl phosphite.
8. A lithium-ion electrochemical cell comprising:
an anode;
a cathode;
an electrolyte interspersed between the anode and the cathode, wherein the electrolyte comprises a mixture of:
an ethylene carbonate (EC);
an ethyl methyl carbonate (EMC);
a fluorinated co-solvent selected from the group consisting 2,2,2-trifluoroethyl butyrate (TFEB), di-2,2,2-trifluoroethyl carbonate (DTFEC), 2,2,2-trifluoroethyl methyl carbonate (TFEMC), mono-fluoroethylene carbonate (FEC), ethyl trifluoroacetate (ETFA), 2,2,2-trifluoroethyl acetate (TFEA), 2,2,2-trifluoroethyl propionate (TFEP), ethyl-2,2,2-trifluoroethyl carbonate (ETFEC), propyl-2,2,2-trifluoroethyl carbonate (PTFEC), methyl-2,2,2,2′,2′,2′-hexafluoro-i-propyl carbonate (MHFPC), ethyl-2,2,2,2′,2′,2′-hexafluoro-i-propyl carbonate (EHFPC), fluoropropylene carbonate (FPC), trifluoropropylene carbonate (TFPC), methyl nonafluorobutyl ether, 2,2,3,3,3-pentafluoropropyl methyl ether, 1,1,3,3,3-pentafluoro-2-trifluoromethyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, and perfluoropolyether;
a flame retardant additive selected from the group consisting of triphenyl phosphate (TPhPh/TPP/TPPa), tributyl phosphate (TBuPh), triethyl phosphate (TEtPh), bis(2,2,2-trifluoroethyl) methyl phosphonate (TFMPo), triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, tris(2,2,2-trifluoroethyl) phosphite, diethyl ethylphosphonate, and diethyl phenylphosphonate; and,
a lithium salt,
wherein the electrochemical cell operates in a temperature range of from about −50 degrees Celsius to about 60 degrees Celsius and further wherein the electrolyte comprises from about 5% to about 30% by volume flame retardant additive.
9. A lithium-ion electrochemical cell comprising:
an anode;
a cathode;
an electrolyte interspersed between the anode and the cathode, wherein the electrolyte comprises a mixture of:
an ethylene carbonate (EC);
an ethyl methyl carbonate (EMC);
a fluorinated co-solvent selected from the group consisting 2,2,2-trifluoroethyl butyrate (TFEB), di-2,2,2-trifluoroethyl carbonate (DTFEC), 2,2,2-trifluoroethyl methyl carbonate (TFEMC), mono-fluoroethylene carbonate (FEC), ethyl trifluoroacetate (ETFA), 2,2,2-trifluoroethyl acetate (TFEA), 2,2,2-trifluoroethyl propionate (TFEP), ethyl-2,2,2-trifluoroethyl carbonate (ETFEC), propyl-2,2,2-trifluoroethyl carbonate (PTFEC), methyl-2,2,2,2′,2′,2′-hexafluoro-i-propyl carbonate (MHFPC), ethyl-2,2,2,2′,2′,2′-hexafluoro-i-propyl carbonate (EHFPC), fluoropropylene carbonate (FPC), trifluoropropylene carbonate (TFPC), methyl nonafluorobutyl ether, 2,2,3,3,3-pentafluoropropyl methyl ether, 1,1,3,3,3-pentafluoro-2-trifluoromethyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, and perfluoropolyether;
a flame retardant additive selected from the group consisting of triphenyl phosphate (TPhPh/TPP/TPPa), tributyl phosphate (TBuPh), triethyl phosphate (TEtPh), bis(2,2,2-trifluoroethyl) methyl phosphonate (TFMPo), triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, tris(2,2,2-trifluoroethyl) phosphite, diethyl ethylphosphonate, and diethyl phenylphosphonate; and,
a lithium salt,
wherein the electrochemical cell operates in a temperature range of from about −50 degrees Celsius to about 60 degrees Celsius and further wherein the electrolyte comprises 1.0 M LiPF 6 lithium salt in 20% by volume ethylene carbonate (EC) plus 55% by volume ethyl methyl carbonate (EMC) plus 20% by volume 2,2,2-tri-fluoroethyl butyrate (TFEB) plus 5% by volume triphenyl phosphate (TPhPh/TPP/TPPa).