Composition analysis of the solid electrolyte interphase film on carbon electrode of lithium-ion battery based on lithium difluoro(oxalate)borate and sulfolane

As a promising salt for lithium-ion batteries, lithium difluoro(oxalate)borate (LiODFB) has become a research hotspot in recently. In this work, LiODFB-based electrolytes are studied. When used in Li/MCMB (mesophase carbon microbeads) cells, cell with 0.9 M LiODFB–ethyl methyl carbonate (EMC)/sulfolane (SL) (1:1, v/v) electrolyte shows lower impedance than ones with 0.9 M LiODFB–EMC/ethylene carbonate (EC) (1:1, v/v) electrolyte. Reduction of impedance mainly dues to the fitting nature of solid electrolyte interphase (SEI) film on carbon electrode of lithium-ion battery. The changing morphologies of SEI films with increased circulation numbers were analyzed by scanning electron microscope (SEM). And C2H5OLi, C2H5CO3Li, Li2CO3, RSO3Li, Li2SO3, LiF, C2H5F and some complicated mesh compounds based on >B–O– bond, were found in SEI film by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was believed that the root of impedance reduction benefits from both the rich existence of sulfurous compounds and the low content of LiF in SEI film.

► When used in Li/MCMB cells LiODFB–EMC/SL electrolyte exhibit low impedance of SEI film.
► SEI film undergoes a smoothing and destroying process as cycling.
► Compositions of the SEI film in Li/MCMB cell with LiODFB–EMC/SL electrolyte contain at least C2H5OLi, C2H5CO3Li, Li2CO3, RSO3Li, Li2SO3, LiF, C2H5F and some complicated mesh compounds based on >B–O– bond.
► Impedance reduction benefits from both the rich existence of sulfurous compounds and the low content of LiF in SEI film.