Analysis Of Carbonate Decomposition During Solid Electrolyte Interphase Formation In Isotope-Labeled Lithium Ion Battery Electrolytes: Extending The Knowledge About Electrolyte Soluble Species

Sufficient interphase formation during the first cycles is crucial for the long-term performance of lithium ion batteries. During the first cycles, electrolyte salt and solvent molecule decomposition caused by electrochemical instabilities leads to a wide range of decomposition species contributing to the formation of performance-beneficial interphases at the electrodes as well as performance-impairing side reactions. Due to structural similarities of carbonate educts, elucidation of underlying reaction pathways is complex. In this work, isotope-labeled ethylene carbonate (C-13(3)-EC) is applied to differentiate contributions of cyclic and linear carbonates to occurring interphase and decomposition reactions. Thereby, carbon atom tracing of electrolyte soluble species is performed by means of gas chromatography-mass spectrometry (GC-MS). Reaction pathways are postulated based on identified molecular origins. Among others, a new DMC-EC cross reactivityvialithium ethylene monocarbonate is considered. Moreover, radical reactions resulting in C-C bond formation are investigated and radical polymerizations of stoichiometric equivalents of ethene formedin situduring EC reduction are proposed. Finally, alkyl carbonates with C(>4)alkyl chains are identified considering underlying reactivities. Discussed electrolyte decomposition reactions extend the understanding of EC-based solid electrolyte interphase (SEI) formation emphasizing possible radical reactivities and solvent molecule contributions.