Magnesium and Aluminum in Contact with Liquid Battery Electrolytes: Ion Transport through Interphases and in the Bulk

A significant challenge in improving Mg and Al batteries is the limited
understanding of the solid electrolyte interphase (SEI) and its evolution under
operating conditions. Additionally, the cationic transference number of related
electrolytes is crucial for their performance as well as potential dendrite formation
yet it is only rarely determined experimentally. Here, we study Al and Mg systems using
Grignards as electrolytes for the Mg case and an ionic liquid electrolyte for the Al case.
The activation energies associated with ion transport through the SEI suggest that it
initially contains a high contribution from liquid pathways for the Mg case and is dense
for the Al case, but becomes fully dominated by liquid pathways after a longer contact with the electrolyte. The initial effective
Mg cationic transference number of the Grignards is close to zero and increases significantly after only one cyclic voltammetry
cycle.