Toward Improved Anodic Stability of Ether-Based Electrolytes for Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMBs) are one of the promising energy-storage technologies for sustainable energy storage due to the abundant resources and intrinsically remarkable energy-storage properties of magnesium metal. However, to compete with alternative technologies, such as present lithium-ion batteries, there is a need to improve their energy density. One of the approaches to accomplish the above demand is to use high-voltage cathodes. The poor anodic stability of the current ether-based electrolytes compatible with magnesium metal anodes limits their working voltage and the choice of electrode materials. In this study, we explored different organic solvent-based electrolytes to design anodically stable ether-based electrolyte solutions for RMB applications. Through comprehensive experimental and computational surveys, we found that the intrinsic electrochemical/chemical stabilities against magnesium metal and the well-balanced solvating ability were necessary to achieve the desired functionality. Based on this knowledge, we designed and synthesized glyme analogues bearing trifluoroalkyl groups. Consequently, we developed anodically stable electrolytes that support electrochemical magnesium deposition/dissolution by combining suitable fluorinated glyme-based solvents with appropriate conducting salts. These electrolytes showed a remarkable anodic limit of 4.4 V vs Mg2+/Mg (the highest ever reported to the best of our knowledge) and effectively suppressed the undesired corrosion of Al current collectors. However, these electrolytes could not be applied to RMBs with high-voltage oxide-based cathodes. Fragility against oxide-based cathodes caused undesired catalytic decomposition of the fluorinated solvents during charging.