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

The narrow electrochemical stability window, deleterious side reactions, and zinc dendrite growth all act to prevent the practical use of aqueous zinc-ion batteries. Here, aqueous "soggy-sand" electrolytes (synergistic electrolyte-insulator dispersions) with multiple functions have been developed for achieving high-voltage Zn-ion batteries. We reveal how these electrolytes bring a unique combination of benefits, synergizing the advantages of solid and liquid electrolytes. 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 the solvation of Zn 2+ , thereby influencing the mechanical and electrochemical properties, and causing the Mn 2+ in the solution to be oxidized and thus providing additional capacity. As a result, the best performing Al 2 O 3 -based "soggy-sand" electrolyte exhibits a long-life of 2500 h and dendrite-free deposition behavior in Zn||Zn cells. Furthermore, it increases the charging cut-off voltage for Zn/MnO 2 full cells to 2 V (versus Zn 2+ /Zn), allowing for an extremely high specific capacity of 344 mAh g -1 at 1 A g -1 to be attained. Even under practical conditions with a high mass 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 thus provides a new approach for the design of powerful and universal electrolyte for aqueous batteries. This article is protected by copyright. All rights reserved.