Lithium salt mixture and uses thereof as a battery electrolyte

1. An electrolyte composition, comprising:

(i) at least three lithium salts, the at least three lithium salts being:

lithium bis(fluorosulfonyl)imide;

from 5 mol % to 40 mol % lithium 2-trifluoromethyl-4,5-dicyanoimidazolate; and

lithium hexafluorophosphate;

(ii) only one solvent or solvent mixture consisting of ethers, carbonates, esters, ketones, partially hydrogenated hydrocarbons, nitriles, amides, alcohols, nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone and 3-methyl-2-oxazolidinone; and

(iii) optionally at least one electrolytic additive.

2. The composition as claimed in claim 1 , wherein the lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate and lithium 2-trifluoromethyl-4,5-dicyanoimidazolate salts represent 100% of all of the salts present in the composition.

3. The composition as claimed in claim 1 , wherein the molar concentration of the mixture is less than or equal to 5 mol/l.

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

at least 0.05 mol/l of lithium bis(fluorosulfonyl)imide; and/or

at least 0.05 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate; and/or

at least 0.05 mol/l of lithium hexafluorophosphate.

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

i)

from 0.05 to 0.90 mol/l of lithium bis(fluorosulfonyl)imide;

from 0.05 to 0.90 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate; and

from 0.05 to 0.90 mol/l of lithium hexafluorophosphate;

or

ii)

from 0.2 to 0.90 mol/l of lithium bis(fluorosulfonyl)imide;

from 0.05 to 0.60 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate; and

from 0.05 to 0.60 mol/l of lithium hexafluorophosphate;

or

iii)

from 0.3 to 0.70 mol/l of lithium bis(fluorosulfonyl)imide;

from 0.1 to 0.50 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate; and

from 0.1 to 0.50 mol/l of lithium hexafluorophosphate;

or

iv)

from 0.35 to 0.60 mol/l of lithium bis(fluorosulfonyl)imide;

from 0.15 to 0.50 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate; and

from 0.15 to 0.50 mol/l of lithium hexafluorophosphate;

or

v)

from 0.35 to 0.50 mol/l of lithium bis(fluorosulfonyl)imide;

from 0.20 to 0.40 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate; and

from 0.20 to 0.40 mol/l of lithium hexafluorophosphate;

or

vi)

from 0.35 to 0.45 mol/l of lithium bis(fluorosulfonyl)imide;

from 0.25 to 0.35 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate; and

from 0.25 to 0.35 mol/l of lithium hexafluorophosphate;

or

vii)

0.40 mol/l of lithium bis(fluorosulfonyl)imide;

0.30 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate; and

0.30 mol/l of lithium hexafluorophosphate;

or

viii)

0.50 mol/l of lithium bis(fluorosulfonyl)imide;

0.20 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate; and

0.30 mol/l of lithium hexafluorophosphate.

6. The composition as claimed in claim 1 , wherein the solvent is a solvent mixture consisting of any combination of ethers, carbonates, esters, ketones, partially hydrogenated hydrocarbons, nitriles, amides, alcohols, nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, or 3-methyl-2-oxazolidinone.

7. The composition as claimed in claim 1 , wherein the solvent is a mixture of carbonates.

8. The composition as claimed in claim 1 , wherein the composition comprises the electrolytic additive, wherein 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, t-butylphenol, di-t-butylphenol, tris(pentafluorophenyl)borane, 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.

9. The composition as claimed in claim 1 , chosen from one of the following compositions comprising:

i) 0.40 mol/l of lithium bis(fluorosulfonyl)imide, 0.30 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate, and 0.30 mol/l of LiPF 6 , with fluoroethylene carbonate as the optional electrolytic additive;

ii) 0.50 mol/l of lithium bis(fluorosulfonyl)imide, 0.20 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate, and 0.30 mol/l of LiPF 6 , with fluoroethylene carbonate as the optional electrolytic additive;

iii) 0.45 mol/l of lithium bis(fluorosulfonyl)imide, 0.20 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate, and 0.35 mol/l of LiPF 6 , with fluoroethylene carbonate as the optional electrolytic additive;

iv) 0.50 mol/l of lithium bis(fluorosulfonyl)imide, 0.10 mol/l of lithium 2-trifluoromethyl-4,5-dicyanoimidazolate, and 0.40 mol/l of LiPF 6 , with fluoroethylene carbonate as the optional electrolytic additive.

10. A Li-battery comprising the composition according to claim 1 .

11. An electrochemical cell comprising a negative electrode, a positive electrode and the 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 .