Controlling electrode/electrolyte interfaces is an essential factor to prevent battery failure and improve cycling and lifetime performance. Here we show that the unique character of interfacial chemistry challenges the very idea of combining two well-behaved components and expecting a stable interface. To investigate this phenomenon, we studied the interfacial properties of a well-established chemically and electrochemically stable electrolyte, magnesium (II) bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) in diethylene glycol dimethyl ether (diglyme) against a metallic Mg electrode. Using in situ X-ray photoelectron spectroscopy capable of probing a solid/liquid interface, we show an intrinsic chemical instability at the interface between these conventionally perceived stable electrode and electrolyte materials. First-principles calculations reveal the mechanisms for solvent (diglyme) and salt (MgTFSI) decomposition driven by a hydroxide ion attack of molecule a chelating the Mg2+ dication at defective sites on the electrode surface or in contact ion pairs. This study reveals the counter-intuitive mechanism of interfacial electrolyte decomposition, provides insight into cation-dependent stability for solvation structures across a broad family of solvents. The proposed atomistic guidance for how to improve electrolyte/electrode design and selection provides a path to overcome the non-trivial role of interfacial chemistry and may enhance future battery technologies.

Revealing mechanisms for electrolyte decomposition from first-principles consistent with operando X-ray photoemission spectra

254th National Meeting (2017)

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