Improving Safe Properties of Pp13TFSI Based Electrolyte for High-Voltage Graphite/Li[Li<sub>0.2</sub>Mn<sub>0.54</sub>Ni<sub>0.13</sub>Co<sub>0.13</sub>]O<sub>2</sub> Battery

Safety is the key-feature of high energy density lithium-ion batteries and thermal stability of the electrolytes is crucial. In this work, the thermal and flammability properties of mixed electrolytes based on the conventional ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) (1:1:1 v/v/v), 1M LiPF 6 and the hydrophobic ionic liquid (IL) N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (Pp13TFSI) have been investigated. The mixed electrolyte is observed to be nonflammable at the Pp13TFSI contents of more than 40 vol.%. And physical and electrochemical characteristics of high energy density lithium ion batteries based on Li [Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 as the cathode and artificial graphite as the anode with mixed electrolyte are also investigated. The cell of graphite/ Li [Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 with 1 mol/L LiPF6/40%Pp13TFSI + 60% (EC+DMC+EMC) (1/1/1,v/v/v) electrolyte shows first charge capacity of 313.8 mAh g-1 and discharge capacity of 201.8 mAh g-1, respectively. Moreover, the nail penetration tests are carried out on the charged lithium-ion cells after formation, and the results show no explosion, ignition, or thermal runaway. These results suggest that the IL has potential to improve the safety of lithium ion batteries and can be used to fabricate the high energy density lithium ion batteries for electric vehicles and hybrid electric vehicles.