Correlation of metal anode reversibility with solvation chemistry and interfacial electron transfer in aqueous electrolytes

Reversible electrodeposition of metals is a crucial route to developing high-energy and rechargeable batteries. However, uncontrolled and nonplanar morphological evolution and parasitic reactions at the metal anodes are fundamental barriers to realizing full reversibility. Here, using aqueous electrochemistry as a probe, we develop multiscale characterization tools that can precisely determine the root cause of these morphological instabilities and parasitic reactions. Our analysis indicates that these issues are fundamentally from the free water molecules in aqueous electrolytes, leading to low reversibility of metal anodes. We therefore demonstrate a straightforward and effective strategy, based on modulating the solute anions in aqueous electrolytes, to suppress free water molecule concentration in conventional aqueous electrolytes. A proof of concept is demonstrated using a Zn metal anode, which shows unprecedented reversibility and stability in conventional aqueous electrolytes with structure-making anions under a harsh condition of 10 milliampere hours per square centimeter. This work unlocks an alternative angle to develop sustainable electrolytes for cost-efficient, practical battery chemistries.