Aqueous Rechargeable Magnesium Battery with a High Output Voltage Using a Hydrated Eutectic Electrolyte

Rechargeable magnesium batteries offer safe and cost-effective energy storage but are constrained by narrow electrochemical stability windows, interfacial instability, and sluggish Mg2+ transport. To address these issues, a multi-component hydrated eutectic electrolyte was designed, composed of Mg(ClO4)2, acetamide, caprolactam, and H2O (DM11). This electrolyte reconstructs the hydrogen-bonding network and lowers H2O activity; thereby, the electrochemical stability window is broadened to 4 V. Moreover, acetamide and caprolactam adsorb on the Mg surface and undergo interfacial reactions. This process forms an organic-inorganic hybrid layer that isolates Mg from H2O and reduces corrosion. Benefiting from these synergistic effects, a symmetric Mg//Mg cell with the DM11 electrolyte demonstrated stable cycling for over 500 h, while a Mg//Mg-MnO2 full battery delivered a reversible capacity of 300 mA h g-1 at 0.1 A g-1 with an output voltage of 1.8 V and stable cycling for more than 500 cycles at 0.5 A g-1. This study highlights a viable strategy for engineering hydrated eutectic electrolytes to enhance the stability and electrochemical performance of magnesium batteries.