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Abstract
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 on our ability to elucidate electrochemical reactivity, we 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 its decomposition does not meaningfully contribute to gas evolution. The combined theoretical-experimental approach developed here provides a means to elucidate electrolyte reactivity, improving our ability to predict decomposition products and pathways when initially unknown.
Supplementary materials
Title
Supplementary Information: Chemical Reaction Networks Explain Gas Evolution Mechanisms in Mg-Ion Batteries
Description
Schematic of experimental setup; cyclic voltammetry data; snapshot OEMS spectra; discussion of solvent corrections to free energy; discussion of predicted reduction potentials with and in the absence of explicit solvent; further description of CRN-predicted products; average stochastic trajectories obtained during CRN analysis; SEM images.
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Data for "Chemical Reaction Networks Explain Gas Evolution Mechanisms in Mg-Ion Batteries"
Description
This repository contains two files: madeira.json and pathway_data.json.
madeira.json contains the MAgnesium Dataset of Electrolyte and Interphase ReAgents (MADEIRA) - structural, thermochemical, redox, and vibrational properties of 11,502 species relevant to electrolyte decomposition and solid electrolyte interphase formation in Mg-ion batteries. All properties in MADEIRA were calculated using the Q-Chem electronic structure code at the ωB97X-V/def2-TZVPPD/SMD level of theory, with SMD parameters appropriate for G2.
pathway_data.json contains the thermochemical and structural properties of 31 ground-state minima and 15 transition-states relevant to the decomposition of G2 and the formation of evolved gases. These species are named in the same way as they are in the manuscript text. Properties were initially obtained using the Jaguar electronic structure code at the ωB97X-D/def2-SVPD/PCM level of theory with the dielectric constant of water; the electronic energy was then re-calculated at a higher level of theory (ωB97M-V/def2-TZVPD/PCM).
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