Room Temperature Ionic Liquid as Electrolyte for Lithium-Ion Battery

Abstract

Applicability of RTIL as electrolyte for lithium ion battery was assessed using coin-cells with Li[Li0.2Mn0.54Ni0.13Co0.13]O2 as cathode, metallic lithium foil as anode, Cellgard 2300 as separator and LiTFSI-Py14TFSI as electrolyte. Those with LiTFSI higher than 0.4 M showed a high initial discharge capacity (190 mAh/g at 0.2 C) and good cycling stability (> 98% coulombic efficiencies) after first cycle. Change upon cycling and storage was investigated by impedance measurement at open circuit potential (ca. 3 V) with results showing a relatively high resistance, 10 ~ 20 Ω for electrolyte resistance (Re) and 100 ~ 200 Ω for SEI and charge transfer resistance (Rsei + Rct). As the total resistance is stable after storage for 30 days, good stability of the cathode/IL electrolyte and Li/IL electrolyte interface is indicated. The use of Py14TFSI-added mixed electrolyte system to enhance current rating and reduce fire hazards were studied with results discussed.