Stabilizing the Solid Electrolyte Interphase of SiOx Negative Electrodes: The Role of Fluoroethylene Carbonate in Enhancing Electrochemical Performance

This study examined the role of fluoroethylene carbonate (FEC) in stabilizing the solid electrolyte interphase (SEI) and enhancing the electrochemical performance of SiOx-based composite negative electrodes in lithium-ion batteries. Two electrolyte systems were used: 1.0 mol dm-3 (M) LiPF6 in a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with 0.5 wt.% VC, and 1.0 M LiPF6 in a mixture of EC and EMC with 1.0 wt.% VC and 10 wt.% FEC. These systems enabled the investigation of how FEC contributes to SEI stabilization and cycling stability. FEC promotes the formation of a LiF-rich SEI layer, which mitigates volume expansion and enhances capacity retention. Additionally, the accumulation of Li2CO3 and Li2O in the SEI was found to increase interfacial resistance, as observed through electrochemical impedance spectroscopy (EIS). Among the SiOx contents tested (0%, 3%, and 7.8%), the 3% SiOx content exhibited the best balance between SiOx and carbon nanotubes, resulting in improved SEI formation and enhanced electrochemical performance. These results offer insights into the optimization of electrolyte formulations for long-term cycling stability in SiOx-based lithium-ion batteries.