Lithium salt mixture and uses thereof as a battery electrolyte

1. An electrolyte composition comprising a lithium salt mixture, wherein the lithium salt mixture comprises:

from 85 mol % to 99.9 mol % of lithium bis(fluorosulfonyl)imide; and

from 0.1 mol % to 15 mol % of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate,

wherein the electrolyte composition further comprises at least one solvent and at least one electrolytic additive in addition to the lithium salt mixture,

wherein the at least one solvent is chosen from the group consisting of dimethoxyethane, dioxolane, dioxane, dibutyl ether, tetrahydrofuran, carbonates, esters, ketones, partially hydrogenated hydrocarbons, nitriles, amides, alcohols, sulfoxides, sulfolane, nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)- pyrimidinone, 3-methyl-2-oxazolidinone and their mixtures,

wherein the content of the electrolytic additive in the electrolyte composition is between 0.01 wt % and 10 wt %.

2. The composition as claimed in claim 1 , comprising:

lithium bis(fluorosulfonyl)imide in one of the following molar percentages: from 85% to 99%, from 85% to 98.5%, from 85% to 98%, from 85% to 97.5%, from 85% to 97%, from 85.5% to 99.9%, from 86% to 99.9%, from 86% to 99.5%, from 86.5% to 99.5%, from 87% to 99.5%, from 87% to 99%, from 87.5% to 99.9%, from 87.5% to 99.5%, from 87.5% to 99%, from 88% to 99.9%, from 88% to 99.5%, from 88% to 99%, from 89% to 99.9%, from 89% to 99.5%, from 89% to 99%, from 89.5% to 99.9%, from 89.5% to 99.5%, from 89.5% to 99%, from 90% to 99.9%, from 90% to 99.5%, from 90% to 99.5%, from 90% to 99%, from 90% to 98.5%, from 90% to 98%, from 90% to 97.5%, from 90% to 97%, from 90% to 96.5%, from 90% to 96%, from 91% to 99.9%, from 91% to 99.5%, from 91% to 99%, from 91% to 98.5%, from 91% to 98%, from 91% to 97.5%, from 91% to 97%, from 91% to 96.5%, from 91% to 96%, from 92% to 99.9%, from 92% to 99.5%, from 92% to 99%, from 92% to 98.5%, from 92% to 98%, from 92% to 97.5%, from 92% to 97%, from 92% to 96.5%, from 92% to 96%, from 93% to 99.9%, from 93% to 99.5%, from 93% to 99%, from 93% to 98.5%, from 93% to 98%, from 93% to 97.5%, from 93% to 97%, from 93% to 96.5%, from 93% to 96%, from 94% to 99.9%, from 94% to 99.5%, from 94% to 99%, from 94% to 98.5%, from 94% to 98%, from 94% to 97.5%, from 94% to 97%, from 94% to 96.5%, from 94% to 96%, from 95% to 99.9%, from 95% to 99.5%, or from 95% to 99%; and

lithium 2-trifluoromethyl-4,5-dicyanoimidazolate in one of the following molar percentages: from 15% to 1%, from 15% to 1.5%, from 15% to 2%, from 15% to 2.5%, from 15% to 3%, from 14.5% to 0.1%, from 14% to 0.1%, from 14% to 0.5%, from 13.5% to 0.5%, from 13% to 0.5%, from 13% to 1%, from 12.5% to 0.1%, from 12.5% to 0.5%, from 12.5% to 1%, from 12% to 0.1%, from 12% to 0.5%, from 12% to 1%, from 11% to 0.1%, from 11% to 0.5%, from 11% to 1%, from 10.5% to 0.1%, from 10.5% to 0.5%, from 11.5% to 1%, from 10% to 0.1%, from 10% to 0.5%, from 10% to 1%, from 10% to 1.5%, from 10% to 2%, from 10% to 2.5%, from 10% to 3%, from 10% to 3.5%, from 10% to 4%, from 9% to 0.1%, from 9% to 0.5%, from 9% to 1%, from 9% to 1.5%, from 9% to 2%, from 9% to 2.5%, from 9% to 3%, from 9% to 3.5%, from 9% to 4%, from 8% to 0.1%, from 9% to 0.5%, from 8% to 1%, from 8% to 1.5%, from 8% to 3%, from 8% to 2.5%, from 8% to 3%, from 8% to 3.5%, from 8% to 4%, from 7% to 0.1%, from 7% to 0.5%, from 7% to 1%, from 7% to 1.5%, from 7% to 2%, from 7% to 2.5%, from 7% to 3%, from 7% to 3.5%, from 7% to 4%, from 6% to 0.1%, from 6% to 0.5%, from 6% to 1%, from 6% to 1.5%, from 6% to 2%, from 6% to 2.5%, from 6% to 3%, from 6% to 3.5%, from 6% to 4%, from 5% to 0.1%, from 5% to 0.5%, or from 5% to 1%.

3. The composition as claimed in claim 1 , in which:

the molar percentage of lithium bis(fluorosulfonyl)imide is greater than or equal to 95%; and

the molar percentage of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate is between 0.1% and 5% .

4. The composition as claimed in claim 1 , comprising:

from 86 mol % to 99.9 mol % of lithium bis(fluorosulfonyl)imide; and

from 14 mol % to 0.1 mol % of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate.

5. The composition as claimed in claim 1 , in which the molar concentration of lithium bis(fluorosulfonyl)imide and lithium 2-trifluoromethyl-4,5-dicyanoimidazolate in the electrolyte composition is between 0.85 mol/l and 5 mol/l.

6. The composition as claimed in claim 1 , comprising:

from 0.85 to 0.999 mol/l of lithium bis(fluorosulfonyl)imide; and

from 0.15 to 0.001 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate.

7. The composition as claimed in claim 1 , comprising:

from 0.86 to 0.999 mol/l of lithium bis(fluorosulfonyl)imide; and

from 0.14 to 0.001 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate.

8. The composition as claimed in claim 1 , in which the solvent is chosen from carbonates and their mixtures.

9. The composition as claimed in claim 1 , in which the electrolytic additive is chosen from the group consisting of fluoroethylene carbonate, vinylene carbonate, 4-vinyl-1,3-dioxolan-2-one, pyridazine, vinylpyridazine, quinoline, vinylquinoline, butadiene, sebaconitrile, LiB(C 2 O 4 ) 2 , lithium nitrate, alkyl disulfides, fluorotoluene, 1,4-dimethoxytetrafluorotoluene, oximes, aliphatic epoxides, halogenated biphenyls, methacrylic acids, allyl ethyl carbonate, vinyl acetate, divinyl adipate, acrylonitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, phosphonates, silane compounds containing a vinyl, 2-cyanofuran, and mixtures thereof.

10. A method of operating a Li-ion battery, the battery comprising an electrolyte composition as claimed in claim 1 , wherein the method comprises operating the battery at a temperature range of between −30° C. and 65° C.

11. An electrochemical cell comprising a negative electrode, a positive electrode and an electrolyte composition as claimed in claim 1 , interposed between the negative electrode and the positive electrode.

12. A battery comprising at least one electrochemical cell as claimed in claim 11 .

13. The composition as claimed in claim 1 , wherein the mixture comprises:

from 95 mol % to 99.9 mol % of lithium bis(fluorosulfonyl)imide; and

from 0.1 mol % to 5 mol % of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate.

14. A method of operating a Li-ion battery, the battery comprising the composition as claimed in claim 13 , wherein the method comprises operating the battery at a temperature range of between −30° C. and 65° C.