Targeted research on the single role of lithium Bis(oxalate)borate in the film-forming process through a novel lithium salt-free electrolyte system

A blank comparison group of lithium salt-free electrolyte system, replacing the lithium salt of electrolyte with a redox shuttle agent, is constructed to give targeted research on the single role of lithium bis(oxalate)borate (LiBOB) salt, especially of bis(oxalate)borate anions (BOB − ) in the film-forming process. By combining and comparing all available studies, such as attenuated total reflectance (IR-ATR), X-Ray photoelectron diffraction spectrum (XPS), electrochemical impedance spectrum (EIS), scanning electron microscopy (SEM) tests and quantum chemical calculation , the formation mechanism of the solid electrolyte interphase (SEI) film is proposed. Results reveal that the prior reduction of BOB − anions can postpone the reduction potential and hinder the decomposition rate of carbonate solvents, but promote the formation of a dense, conductive and effective SEI film. This work provides a novel way to investigate the film-forming mechanism and has guiding significance for revealing the effect of other kinds of lithium salts on the surface film formation.