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.