Chemical Reaction Networks Explain Gas Evolution Mechanisms in Mg-Ion Batteries

Out-of-equilibrium electrochemical reaction mechanismsare notoriouslydifficult to characterize. However, such reactions are critical fora range of technological applications. For instance, in metal-ionbatteries, spontaneous electrolyte degradation controls electrodepassivation and battery cycle life. Here, to improve our abilityto elucidate electrochemical reactivity, we for the first time combinecomputational chemical reaction network (CRN) analysis based on densityfunctional theory (DFT) and differential electrochemical mass spectroscopy(DEMS) to study gas evolution from a model Mg-ion battery electrolyte-magnesium bistriflimide (Mg-(TFSI)(2)) dissolved in diglyme (G2). AutomatedCRN analysis allows for the facile interpretation of DEMS data, revealingH(2)O, C2H4, and CH3OH asmajor products of G2 decomposition. These findings are further explainedby identifying elementary mechanisms using DFT. While TFSI- is reactive at Mg electrodes, we find that it does not meaningfullycontribute to gas evolution. The combined theoretical-experimentalapproach developed here provides a means to effectively predict electrolytedecomposition products and pathways when initially unknown.