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

Strengthening water (H 2 O) interaction is a universal strategy for reducing H 2 O 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). LiMn 2 O 4 ||Li 4 Ti 5 O 12 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.