Out-of-equilibrium electrochemical reaction mechanisms
are notoriously
difficult to characterize. However, such reactions are critical for
a range of technological applications. For instance, in metal-ion
batteries, spontaneous electrolyte degradation controls electrode
passivation and battery cycle life. Here, to improve our ability
to elucidate electrochemical reactivity, we for the first time combine
computational chemical reaction network (CRN) analysis based on density
functional 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). Automated
CRN analysis allows for the facile interpretation of DEMS data, revealing
H2O, C2H4, and CH3OH as
major products of G2 decomposition. These findings are further explained
by identifying elementary mechanisms using DFT. While TFSI–is reactive at Mg electrodes, we find that it does not meaningfully
contribute to gas evolution. The combined theoretical–experimental
approach developed here provides a means to effectively predict electrolyte
decomposition products and pathways when initially unknown.