Ionic liquid electrolyte for lithium-ion batteries
The ionic liquids disclosed herein are salts comprising a nitrogen or phosphorus such as a quaternary ammonium ion, a quaternary phosphonium ion, or an N-alkylated nitrogen heterocycle, and which include at least one functional substituent, e.g., a fluoro, cyano, carbonate ester, an alkenyl group, or an alkynyl group bonded to a carbon atom the cation. In a preferred embodiment, the cation is represented by the structure of Formula (I) as described herein.
1. An ionic liquid comprising a cation of Formula (I) and a counter anion:
wherein:
Z 1 is N or P;
x is 1;
R 1 and R 2 together with Z 1 constitute a non-aromatic 5-membered heterocyclic ring;
each of R 3 and R 4 independently comprises an a hydrocarbyl group; and
the non-aromatic 5-membered heterocyclic ring bears at least one substituent selected from the group consisting of a fluoro, cyano, a carbonate ester, alkenyl group, and alkynyl group;
wherein the anion of the ionic liquid is N(SO 2 F) 2 1− (FSI).
2. The ionic liquid of claim 1 , wherein the non-aromatic 5-membered heterocyclic ring is selected from the group consisting of a pyrrolidine and a 3-pyrrolidone.
3. The ionic liquid of claim 1 , wherein one or more carbon of the non-aromatic 5-membered heterocyclic ring bears at least one fluoro substituent.
4. The ionic liquid of claim 1 , wherein Z 1 is N.
5. The ionic liquid of claim 3 , wherein Z 1 is N.
6. An ionic liquid comprising a nitrogen or phosphorous cation and a counter anion, wherein the cation ion has a formula consisting of Formula (III):
wherein:
Z 1 is N or P;
n is an integer from 1 to 8;
each X 2 independently is F, CN, alkenyl, fluoro-substituted alkyl, or cyano-substituted alkyl;
each of R 3 and R 4 independently comprises an a hydrocarbyl group; and
the anion of the ionic liquid is N(SO 2 F) 2 1− (FSI).
7. The ionic liquid of claim 6 , wherein X 2 is F.
8. The ionic liquid of claim 6 , wherein Z 1 is N.
9. The ionic liquid of claim 6 , wherein Z 1 is N, and X 2 is F.
10. An electrolyte for a lithium ion battery comprising a lithium salt dissolved in the ionic liquid of claim 1 .
11. The electrolyte of claim 10 , wherein the lithium salt is selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imidate, lithium 2-trifluoromethyl-4,5-dicyanoimidazolate, lithium 4,5-dicyano-1,2,3-triazolate, lithium trifluoromethanesulfonate, lithium perchlorate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium thiocyanate, lithium bis(fluorosulfonyl)imidate, lithium bis(pentafluoroethylsulfonyl)imidate, lithium tetracyanoborate, lithium nitrate, and a combination of two or more thereof.
12. The electrolyte of claim 10 , wherein the lithium salt is present at a concentration in the range of about 1 molar (M) to about 5 M.