The Effect of Chlorides on the Performance of DME/Mg[B(HFIP)$_4$]$_2$ Solutions for Rechargeable Mg Batteries

One of the major issues in developing electrolyte solutions for rechargeable magnesium batteries is understanding the positive effect of chloride anions on Mg deposition-dissolution processes on the anode side, as well as intercalation-deintercalation of Mg$^{2+}$ ions on the cathode side. Our previous results suggested that Cl$^−$ ions are adsorbed on the surface of Mg anodes and Chevrel phase Mg$_x$Mo$_6$S$_8$ cathodes. This creates a surface add-layer that reduces the activation energy for the interfacial Mg ions transportation and related charge transfer, as well as promotes the transport of Mg$^{2+}$ from the solution phase to the Mg anode surface and into the cathodes' host materials. Here, this work further examines the effect of adding chlorides to the state-of-the-art Mg[B(HFIP)$_4$]$_2$/DME electrolyte solution, specifically focusing on reversible magnesium deposition, as well as the performance of Mg cells with benchmark Chevrel phase cathodes. It was observed that the presence of chlorides in these solutions facilitates both Mg deposition, and Mg$^{2+}$ ions intercalation, whereby this effect is more pronounced as the purity level of the solution is lowered.