Quaternary Ammonium Room-Temperature Ionic Liquid/Lithium Salt Binary Electrolytes: Electrochemical Study

To determine the properties of the quaternary ammonium cation room-temperature ionic liquid [ -diethyl- -methyl- -(2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) amide (DEMETFSA)] used in lithium secondary battery electrolytes, the lithium ionic transport properties of electrolytes, the characteristics of the interface of a cathode and a metallic lithium anode, and battery performance were widely investigated. A DEMETFSA-LiTFSA binary electrolyte showed high chemical stability with lithium metal electrode and a relatively high lithium cationic transport number (0.13), as determined by electrochemical measurements. The prepared [ cathode∣DEMETFSA-LiTFSA binary electrolyte∣lithium metal anode] cell showed sufficient charge/discharge reversibility over (voltage range, ). Moreover, the reversibility of capacities and coulombic efficiencies degraded with increasing upper cutoff voltage owing to cathode/electrolyte interfacial degradation, which were analyzed in detail by impedance measurements.