“Soggy‐Sand” Chemistry for High‐Voltage Aqueous Zinc‐Ion Batteries

Abstract The narrow electrochemical stability window, deleterious side reactions, and zinc dendrites prevent the use of aqueous zinc‐ion batteries. Here, aqueous “soggy‐sand” electrolytes (synergistic electrolyte‐insulator dispersions) are developed for achieving high‐voltage Zn‐ion batteries. How these electrolytes bring a unique combination of benefits, synergizing the advantages of solid and liquid electrolytes is revealed. The oxide additions adsorb water molecules and trap anions, causing a network of space charge layers with increased Zn 2+ transference number and reduced interfacial resistance. They beneficially modify the hydrogen bond network and solvation structures, thereby influencing the mechanical and electrochemical properties, and causing the Mn 2+ in the solution to be oxidized. As a result, the best performing Al 2 O 3 ‐based “soggy‐sand” electrolyte exhibits a long life of 2500 h in Zn||Zn cells. Furthermore, it increases the charging cut‐off voltage for Zn/MnO 2 cells to 2 V, achieving higher specific capacities. Even with amass loading of 10 mg MnO2 cm −2 , it yields a promising specific capacity of 189 mAh g −1 at 1 A g −1 after 500 cycles. The concept of “soggy‐sand” chemistry provides a new approach to design powerful and universal electrolytes for aqueous batteries.