Structure Property and Reaction Mechanism of Boron-Based High-Voltage Electrolyte Additives via First-Principles Calculations

Abstract

Boron-based additives are currently the mainstream film-forming additives. They generate B–F-containing species and then participate in the formation of the cathode–electrolyte interphase (CEI) film. However, little is known about their oxidative decomposition mechanisms, reaction processes, and the relationship between their molecular structure and interface stability in electrolyte. Here, the reaction mechanisms and processes of trimethyl borate (TMB) with fluorides (F–, PF6–, HF, and PF5) in electrolyte were calculated and studied by combining theoretical and experimental methods. TMB was found to be capable of reacting with fluorides and self-dimerize in a nucleophilic manner. In addition, a comparative study was performed with tris(2-cyanoethyl) borate (TCEB), structurally similar to TMB. TMB and TCEB had the same reaction sites and almost the same energy barriers, and they participated in similar reaction processes. The decomposition of boron-based additives was analyzed through simulations and experiments to fill the gap in the information on the reaction mechanisms and processes of boron-based additives. This work also explored the influence of molecular structure on the mechanism of film formation, thus providing theoretical guidance for the molecular structure design of high-pressure additives and offering ideas for developing electrolyte additives.