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.