Differentiating between Ion Transport and Plating–Stripping Phenomena in Magnesium Battery Electrolytes Using Operando Raman Spectroscopy

Understanding metal plating–stripping and mass transport processes is necessary for the development of new electrolytes for post-lithium energy storage applications. Operando vibrational spectroscopy is a valuable analytical tool for this purpose, enabling structural and chemical changes at electrode–electrolyte interfaces to be probed dynamically, under battery cycling conditions. In this work we apply operando Raman spectroscopy to characterize the behavior of the Mg based "all phenyl complex" [Mg2Cl3]+[AlPh4]− in tetrahydrofuran (THF), an exemplar electrolyte for emerging Mg battery technologies. We demonstrate that the observed electrolyte Raman band intensities vary reversibly with electrochemical cycling due to anion migration in response to the applied electric field, while Mg plating and stripping can be monitored independently through the broad background scattering intensity. Spectral measurements across different sites of the platinum working electrode indicate that the ion transport response is spatially heterogeneous, while the plating and stripping response is ubiquitous.