Ionic liquid additive for lithium-ion battery

1. An ionic liquid for adding to an electrolyte of a lithium-ion battery, wherein the ionic liquid comprises a compound with a dual core structure having the general formula (I):

Z 1 X 1 YX 2 Z 2 (formula I),

wherein Z 1 and Z 2 are selected from the group consisting of PF 6 − (hexafluorophosphate), POF 2 − (difluorophosphate), BF 4 − (tetrafluoroborate), B(C 2 O 4 ) 2 − (BOB − , bis(oxalato) borate), BF 2 (C 2 O 4 ) − (ODFB − , difluoro(oxalato)borate), CF 3 BF 3 − (trifluoromethyltrifluoroborate), (FSO 2 ) 2 N − (FSI − , bis(fluorosulfonyl)imide), (CF 3 SO 2 ) 2 N − (TFSI − , bis(trifluoromethane)sulfonamide), CH 3 SO 4 − (MeSO 4 − , methyl sulfate) and

wherein X 1 YX 2 is selected from the group consisting of

1,5-[(1-methylpyrrolidium 1-yl) (triethylamine N-yl)] pentane

1,5-[(1-methylpiperidinium 1-yl) (triethylamine N-yl)] pentane

Bis [2-(1-methylpyrrolidinium 1-yl) ethyl] carbonate

1,5-Bis(1-methylpyrrolidinium 1-yl) pentan-3-one

and

Bis[2-(1-methylpyrrolidinium 1-yl) ethyl] butanedioate

wherein an overall amount of ionic liquid added to the electrolyte is 0.1-15 wt. %.

2. A lithium ion battery comprising a positive electrode, a negative electrode, a separator, an electrolyte and one or more ionic liquid as claimed in claim 1 .

3. The lithium ion battery as claimed in claim 2 further comprising a stabilizer, wherein the stabilizer is a cyclophosphazene compound.

4. The lithium ion battery as claimed in claim 3 , wherein the stabilizer is selected from the group consisting of:

Hexafluoro cyclotriphosphazene; and

Ethoxy (pentafluoro) cyclotriphosphazene.

5. The lithium ion battery as claimed in claim 3 , wherein an amount of the stabilizer added to the electrolyte is 0.1-2.9 wt. %.

6. The lithium ion battery as claimed in claim 2 , wherein a SEI film forming agent is added to the electrolyte.

7. The lithium ion battery as claimed in claim 6 , wherein the SEI film forming agent is selected from the group consisting of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfite (ES), propylene sulfite (PS), and ethylene sulfate (DTD), and combinations thereof.

8. The lithium ion battery as claimed in claim 6 , wherein an amount of the SEI film forming agent added to the electrolyte is 0.1-5 wt. %.

9. The lithium ion battery as claimed in claim 2 , wherein the electrolyte is a non-aqueous electrolyte; wherein optionally, the non-aqueous electrolyte comprises a lithium salt selected from the group consisting of LiPF 6 , LiClO 4 , LiBF 4 , LiSO 3 CF 3 , LiN(SO 2 F) 2 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 CF 2 CF 3 ) 2 , LiAsF 6 , LiAlCl 4 , LiNO 3 , LiPOF 2 , LiB(C 2 O 4 ) 2 , LiBF 2 (C 2 O 4 ), LiCF 3 BF 3 , and combinations thereof; and

wherein optionally, a concentration of the lithium salt in the electrolyte is 0.5˜1.5 mol/L.

10. The lithium ion battery as claimed in claim 9 , wherein the nonauqeous electrolyte comprises an organic solvent selected from the group consisting of carbonate, carboxylate, ether, ketone, and combinations thereof;

wherein optionally, the carbonate is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), dipropyl carbonate, dibutyl carbonate, and a combination thereof;

wherein optionally, the carboxylate is carboxylic acid ester;

wherein optionally, the carboxylic acid ester comprises at least one of methyl acetate, ethyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate and propyl acetate, and a combination thereof; and

wherein optionally, the positive electrode comprises an active material being which is a lithium metal complex oxide compound.

11. The lithium ion battery as claimed in claim 10 , wherein a metal element of the lithium metal complex oxide is selected from the group consisting of a transition metal and a non-transition metal;

wherein optionally, the transition metal is selected from the group consisting of vanadium, titanium, chromium, copper, iron, nickel and cobalt; and

wherein optionally, the non-transition metal is selected from the group consisting of aluminum and manganese.

12. The lithium ion battery as claimed in claim 2 , wherein the negative electrode comprises an active material selected from the group consisting of soft carbon, hard carbon, artificial graphite, natural graphite, meso carbon micro bead (MCMB), silicon, silicon oxide compounds, silicon carbon composites, lithium titanate oxide, and metals that form alloys with lithium;

wherein optionally, the negative electrode comprises an active material that is carbon-based, silicon-based or tin-based;

wherein optionally, the separator comprises a membrane; and

wherein optionally, the membrane comprises a material selected from the group consisting of polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), ceramic material, glass fiber and combinations thereof.