David Prendergast, Lawrence Berkeley National Laboratory
Understanding the Nature of Chemical and Electrochemical Stability of Electrolytes at Mg Anode Surfaces
Written by Aashutosh Mistry
With depleting reserves for lithium, there has been an active interest in making successful secondary batteries using other alkali and alkaline metals. Magnesium is one of the competitors, given reasonably smaller size and high but not extreme reactivity (making it safer). In addition, experimentally no dendrites are observed on magnesium surfaces, in contrast to lithium metal where dendrite-free electrodeposition is more of a dream than reality.
There are two long-standing problems with Mg—unavailability of a good cathode host and search of a suitable electrolyte that would lead to desired Mg/electrolyte interface. David Prendergast of Lawrence Berkeley National Laboratory and his colleagues have been investigating the science of the Mg/electrolyte interface using a three-pronged approach that involves Ab initio molecular dynamics (AIMD) simulations, x-ray spectral interpretation of in situ chemical/electrochemical tests and condensed phase interfacial modeling. The research question addressed in this talk was whether a combination of good electrode (Mg) and good electrolyte would lead to a good interface, and possibly an interphase as well. They experimented with Mg symmetric cells using Mg(AlCl2BuEt)2 salt in tetrahydrofuran (THF) electrolyte. They found out that even under no electrochemical bias (i.e., open circuit situation), there is a formation of different magnesium compounds on the electrode surface—for example, oxides MgO, hydroxides Mg(OH)2, and carbonate MgCO3. From molecular simulations, the researchers revealed that such reactions are only possible given surface defects on the electrode and which can subsequently lead to electrolyte decomposition. At this stage, they are involved in further electrochemical testing and equivalent modeling. The overall study is of extreme importance and should help identify suitable materials for Mg battery.