Quaternary Ammonium Ionic Liquid Electrolyte for a Silicon Nanowire-Based Lithium Ion Battery

The performance of a silicon nanowire battery anode was investigated in electrolytes consisting of butyl-trimethyl ammonium bis(trifluoromethylsulfonyl)imide (QATFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The lithiation capacity of silicon nanowires in 1 M LiTFSI/QATFSI was low due to the lack of a stable solid–electrolyte interface (SEI) layer. The addition of 10 wt % propylene carbonate to the ionic liquid electrolyte promoted the formation of a stable SEI layer and resulted in substantially higher lithiation capacity. Galvanostatic cycling at a rate of C/20 for silicon half-cells and Si/LiCoO 2 full cells showed good performance with a discharge capacity of ∼2000 mAh/g and Coulombic efficiency of 97% after 50 cycles. The effect of electrolyte additives, including ethylene carbonate and vinylene carbonate, was investigated by chronopotentiometry and electrochemical impedance spectroscopy. Results are discussed in terms of the SEI layer and its influence on battery capacity as well as cycle life.