Active Mechanism of the Interphase Film-Forming Process for an Electrolyte Based on a Sulfolane Solvent and a Chelato-Borate Complex

Electrolytes based on sulfolane (SL) solvents and lithium bis(oxalato)borate (LiBOB) chelato-borate complexes have been reported many times for use in advanced lithium-ion batteries due to their many advantages. This study aims to clarify the active mechanism of the interphase film-forming process to optimize the properties of these batteries by experimental analysis and theoretical calculations. The results indicate that the self-repairing film-forming process during the first cycle is divided into three stages: the initial film formation with an electric field force of ∼1.80 V, the further growth of the preformation solid electrolyte interphase (SEI) film at ∼1.73 V, and the final formation of a complete SEI film at a potential below 0.7 V. Additionally, we can deduce that the decomposition of LiBOB and SL occurs throughout nearly the entire process of the formation of the SEI film. The decomposition product of BOB- anions tends to form films with an irregular structure, whereas the decomposition product of SL is in favor of the formation of a uniform SEI film.