Preparation and Properties of Ionic-Liquid Mixed Solutions as a Safety Electrolyte for Lithium Ion Batteries

The safety of lithium ion batteries becomes an obstacle technique for application of Electric vehicles (EVs), ionic liquids (ILs) are thought as one of the most promising means to solve this problem. In this paper, the mixed ILs is prepared from N-propyl-N-methyl pyrrolidinium bis (trifluoromethanesulfonyl) imide (PYR13TFSI), N-ethyl-N-methyl imidazolium bis (trifluoromethanesulonyl) imide (EMITFSI) (9:1, 7:3, 1:1, v/v). Impedance spectroscopy and linear sweep voltammogram studies show the well stability of mixed ILs to lithium. The cells using 0.2M LiTFSI / EMITFSI-PYR13TFSI (1:1, v/v) electrolyte show good performances and higher coulomb efficiencies (the reversible capacities were 132 mAhg-1 for LiFePO4, 134mAhg-1 for Li4Ti5O12 and 275 mAhg-1 for carbon material). The ionic conductivity and lithium transference number of 0.2M LiTFSI / EMITFSI-PYR13TFSI (1:1, v/v) at room temperature are 4×10−3 S cm−1 and 0.3, respectively. Thermal stability of all ILs is higher than 350°C, all ILs show non-flammability by the burning tests.