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

Abstract 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 LiPF 6 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.