FEC-LiTFSI-Pyr<sub>1A</sub>TFSI Ionic Liquid Electrolyte to Improve Low Temperature Performance of Lithium-Ion Batteries

N-methyl-N-allylpyrrolidinium bis (trifluoromethanesulfonyl) imide (PYR 1A TFSI) with substantial supercooling behavior is synthesized to develop low temperature electrolyte for lithium-ion batteries. Additive fluoroethylene carbonate (FEC) in LiTFSI/PYR 1A TFSI/EC/PC/EMC is found that it can reduce the freezing point. LiFePO 4 /Li coin cells with the FEC-PYR 1A TFSI electrolyte exhibit good capacity retention, reversible cycling behavior at low temperatures. The good performance can be attributed to the decrease in the freezing point and the polarization of the composite electrolyte.