In situ diffuse reflectance infrared Fourier-transformed spectroscopy study of solid electrolyte interphase formation from lithium bis(trifluoromethanesulfonyl)imide in 1,2-dimethoxyethane and 1,3-dioxolane with and without lithium nitrate additive over lithium and copper metal anodes

DRIFTS (diffuse reflectance infrared Fourier-transformed spectroscopy) is applied to study the surface reactions over Li foil and Cu foil anodes when using the electrolyte of LiTFSI (LiN(SO2CF3)2) salt in DME (1,2-dimethoxyethane) and DOL (1,3-dioxolane) solvents, with/without LiNO3 (LN) additive. The DRIFTS spectra at open circuit potential (OCV) indicate that DME and DOL are stable, while LiTFSI is chemically decomposed over Li but stable over Cu anode. The absorbance bands suggest that LiSO2CF3 and Li2NSO2CF3 species formed from LiTFSI decomposition over Li. LN is chemically decomposed over both Li and Cu anodes into LiNO2 with Li2O as the likely accompanying species at OCV. During LSV (linear scan voltammetry) these surface species and also DOL and DME can be electrochemically reduced forming ROLi (CH3CH2OCH2Li/CH3OCH2CH2OLi and CH3OLi, respectively, from DOL and DME), Li3N (from TFSI− and LiNO3), LiF and Li2SO2 (from TFSI−), and Li2O (from LiNO3).