Microstructure Design of Electrolytes for High-Energy-Density Aqueous Batteries

Strengthening water (H2O) interaction is a universal strategy for reducing H2O reactivity, yet often at the expense of kinetics. Here, we unveiled the controllable modulation of molecular structures in aqueous electrolytes and their tailorable electrochemical performance in high-energy aqueous batteries. The H-bond properties and special distributions are identified as crucial parameters to decouple the electrochemical stability and the transport properties of Li+ in the aqueous-based electrolytes. It is found that the mildly solvating ethylene glycol diethyl ether (DEE) is capable of balancing both high-energy Li-ion batteries with a greatly extended electrochemical window of 1.4–5.2 V vs. Li+/Li and high ionic conductivity of 7.2 mS cm–1 at room temperature with a low salt concentration (1.57 mol/L). LiMn2O4||Li4Ti5O12 aqueous cells deliver outstanding cycling performance over 300 cycles at 1C. One Ah pouch cell is demonstrated with a high energy density of 76.76 Wh kg–1 at 0.2C and stable cycling performance at room temperature and a low temperature of −20 °C. This work provides new insights and strategies to design advanced electrolytes for rechargeable batteries.