Ethylene sulfite and vinylene carbonate additives in acetonitrile-containing electrolytes for lithium-ion batteries: SEI impedance and XPS investigation

Electrolyte solvents play a crucial role in extending the operating temperature range of Li-ion batteries. This article emphasizes the importance of precise adjustment of the amount of vinylene carbonate (VC) additive when incorporated with ethylene sulfite (ES) into a 20 vol% acetonitrile-containing carbonate electrolyte, with the aim to achieve enhanced LiNi 0.5 Mn 0.3 Co 0.2 O 2 /graphite pouch cell power performance at −5 °C. After determining the intrinsic characteristics of the electrolyte, including its ionic conductivity, viscosity, and lithium cation solvation shell using Raman spectroscopy analysis, the Li + cation transport properties within the SEI are meticulously examined through the study of the distribution of relaxation times (DRT) extracted from electrochemical impedance spectroscopy (EIS) spectra and its composition elucidated by infrared (IR) and X-ray photoelectron spectroscopy (XPS). This study reveals significant information about the reduction reaction mechanisms leading to varying amounts of ES, VC, lithium bis(fluorosulfonyl)imide (LiFSI), acetonitrile and carbonate reduction compounds in the SEI, some of which are suspected to be the main compounds responsible for the observed differences in power performance.