PEG-based co-solvent aqueous electrolytes enabling high-energy rechargeable aqueous magnesium-ion batteries

Abstract

In contrast to organic electrolyte systems, rechargeable aqueous magnesium-ion batteries (RAMIBs) offer unparalleled advantages, particularly in environmental sustainability, safety, cost-effectiveness, and their potential for large-scale energy storage. However, the practical implementation of RAMIBs has been hindered by the limited electrochemical stability of aqueous electrolytes. Although polyethylene glycol (PEG)-based aqueous electrolytes provide a wide electrochemical window, the poor ionic conductivity has restricted their widespread adoption. In this study, we address this challenge by employing trimethyl phosphate (TMP) and PEG400 as the co-solvent of aqueous magnesium-ion electrolytes. This combination significantly enhances the ionic conductivity to 4.44 mS cm^-1 and increases the electrochemical stability window of the aqueous electrolyte by mitigating the activity of H₂O. In addition, we underscore the role of TMP as a potent co-solvent in modulating the solvation structures of Mg²⁺ ions and modifying the electrochemical behavior of the electrolytes. Leveraging this advancement, in conjunction with a V₂O₅ cathode and a 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) anode, the resulting RAMIBs demonstrate a remarkable discharge capacity of 227.6 mAh g^-1, a large energy density of 157 Wh kg^-1 and a high power density of 70 W kg^-1. Our findings represent a significant stride toward exploiting the full potential of RAMIBs for future energy storage applications.