Exceptional cycling performance of a graphite/Li1.1Ni0.25Mn0.65O2 battery at high voltage with ionic liquid-based electrolyte

An electrolyte composed of lithium difluoro(oxalate)borate (LiDFOB) as lithium salt, N-propyl-N-methylpiperidinium bis(trifuoromethansulfonyl) imide (PP13TFSI) ionic liquid and dimethylcarbonate (DMC) as co-solvent and fluoroethylene carbonate (FEC) as additive is reported in this study. It is found that the resulted ionic liquid-based electrolyte demonstrates high ionic conductivity, low polarization and high safety performance. The Li/Li1.1Ni0.25Mn0.65O2 and Li/Graphite half-cells with the electrolyte exhibit excellent electrochemical performance, retaining capacities of more than 186 mA h g−1 and 361.6 mA h g−1 after 100 cycles, respectively. Such outstanding energy storage performance is ascribed to the joint oxidative decomposition of LiDFOB and FEC, which can form stable and low impedance solid electrolyte interface (SEI) on the Li-rich cathode and graphite anode. Besides, the SEI layer can prevent transition metal dissolution, enabling excellent cycling stability for the high voltage graphite/Li1.1Ni0.25Mn0.65O2 full cell. As a result, the full cell with the ionic liquid based electrolyte maintains a discharge capacity and capacity retention of 180 mAh g−1 and 87.54% after 100 cycles at 0.5 C and 40 °C, far superior to that obtained for commercial electrolyte. All these characteristics make the electrolyte a promising candidate for safe, high performance lithium-ion battery electrolyte.