Rechargeable batteries based on multivalent cations, such as Mg2+ or Ca2+, are promising candidates for next-generation energy storage. However, it has proven exceptionally challenging to construct electrolytes that facilitate reversible charging and discharging, with the repeatable deposition and dissolution of Mg or Ca on to the anode often inhibited by a passivating interfacial layer that forms across the electrode. Fortunately there have been several recent breakthrough candidate electrolytes that appear to address this; however, understanding exactly how these new electrolyte compositions facilitate reversible cycling, and the nature of the interfacial layer that forms, are still uncertain. This project will utilise in-situ liquid-cell transmission electron microscopy (TEM) to visualise the deposition and dissolution dynamics of these new multivalent electrolytes in order to illuminate the mechanisms that allow them to operate reversibly. By combining the insights gleaned from direct imaging with a variety of other techniques that are available at Oxford, including online mass spectrometry and cryo-TEM, it will be possible to correlate the observed deposition morphologies with the chemical constitution of the interfacial layer.