Ethylene bis-carbonates as telltales of SEI and electrolyte health,role of carbonate type and new additives
Résumé
The ethylene bis-carbonate compounds formation is responsible for the earliest change in electrolytecomposition which can be one of the reasons for battery performance decay. In this study, liquid GC/MStechnique is used to detect their formation in electrolytes based on solvent mixtures of EC and differentlinear carbonates (DMC, DEC and EMC), after the first cycle in full cells composed of synthetic graphitepowder/commercial positive films. These compounds stem from linear carbonate electrochemical reduc-tion leading to alkoxide compounds and can be quantified using a selective bicyclic boron ester Lewisacid as an electrolyte additive. Moreover, a quantitative study on ethylene bis-carbonate compounds forwhich the generation profile is different depending on the linear carbonate type, shows that either inbatteries or in a simple chemical mixture of electrolyte and lithium alkoxide, their formation stops whenit reaches a threshold concentration due to the thermodynamic equilibrium. The overall informationis useful for investigating the passivation ability and the dissolution of the Solid Electrolyte Interphase(SEI) that is formed on the negative electrode material. Finally, the passivation property of the SEI freshlyformed with four additives - Vinylene Carbonate (VC), Vinyl Ethylene Carbonate (VEC), Fluoro EthyleneCarbonate (FEC) and 1,3-Propane Sultone (1,3-PS)- is studied.