Study of the Formation of a Solid Electrolyte Interphase (SEI) on a Silicon Nanowire Anode in Liquid Disiloxane Electrolyte with Nitrile End Groups for Lithium-Ion Batteries

The chemical compatibility of the various compounds and elements used in lithium-based batteries dictates their safe operation parameters and performance. The lithium salt Li-bis(trifluoromethanesulfonyl)imide (LiTFSI) has many advantages over the common LiPF₆ salt as it does not react with water impurities to form, for example, hydrofluoric acid. To further accommodate safe-operation chemistry, we use a non-volatile disiloxane-based solvent 1,3-bis(cyanopropyl)tetramethyldisiloxane (TmdSx-CN). This is a liquid disiloxane functionalized with terminal nitrile groups. In this paper, we report on the electrochemical characterization and the composition of the solid electrolyte interphase (SEI) of 1 mol kg⁻¹ LiTFSI dissolved in TmdSx-CN in silicon-lithium batteries. Specifically, we study the SEI formation on silicon nanowire anodes and its composition by several ex-situ surface techniques (XPS, SEM), and in-situ via polarization modulation infrared reflectance absorption spectroscopy (PM-IRRAS). We evaluate the potential application of TmdSx-CN to silicon-lithium batteries and conclude that the addition of fluoroethylene carbonate (FEC) at low concentrations (10 wt %) is essential to the formation of an effective SEI. We anticipate that our study will encourage the investigation, design and use of siloxane-based solvents as safer alternatives to common solvents used in Li-ion batteries, and specifically as candidate solvents in Li-metal and silicon-anode based batteries.