"Soggy-Sand" Chemistry for High-Voltage Aqueous Zinc-Ion Batteries

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 Zn²⁺ 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 Mn²⁺ in the solution to be oxidized. As a result, the best performing Al₂ O₃ -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/MnO₂ 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.