Superior compatibility of silicon nanowire anodes in ionic liquid electrolytes

Silicon nanowire anodes were investigated in lithium-metal cells using different electrolyte formulations based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI) and N-trimethyl-N-butyl-ammonium bis(fluoro sulfonyl)imide (N1114FSI) ionic liquids. The lithium insertion process in the silicon anode was analyzed by cyclic voltammetry measurements, performed at different scan rates and for prolonged cycles, combined with impedance spectroscopy analysis. A galvanostatic charge-discharge cycling test was performed to analyze the electrochemical performances using different types of ionic liquids. A study of the SEI (Solid Electrochemical Interface) layer on the silicon nanowire electrode surface was carried out through X-ray photoelectron spectroscopy (XPS). In general, the silicon anodes in EMIFSI-based electrolytes show very good reversibility, reproducibility, and efficiency in the lithiation process even at high scan rates and exhibits a reversible capacity exceeding 1000 mA h g-1 after 2000 charge-discharge cycles, corresponding to 46 % of the initial value.