Gas Chromatography/Mass Spectrometry As a Suitable Tool for the Li-Ion Battery Electrolyte Degradation Mechanisms Study

To allow electric vehicles to be powered by Li-ion batteries, scientists must understand further their aging processes in view to extend their cycle life and safety. For this purpose, we focused on the development of analytical techniques aiming at identifying organic species resulting from the degradation of carbonate-based electrolytes (EC-DMC/LiPF(6)) at low potential. As ESI-HRMS provided insightful information to the mechanism and chronological formation of ethylene oxide oligomers, we implemented "gas" GC/MS experiments to explore the lower mass range corresponding to highly volatile compounds. With the help of chemical simulation tests, we were able to discriminate their formation pathways (thermal and/or electrochemical) and found that most of the degradation compounds originate from the electrochemically driven linear alkyl carbonate reduction upon cycling and to a lesser extent from a two-step EC reduction. Deduced from these results, we propose an overall electrolyte degradation scheme spanning the entire mass range and the chemical or electrochemical type of processes.