Regulating the solvation structures through a high-entropy strategy for wide-temperature zinc-ion batteries

Abstract

Zinc-ion batteries (ZIBs) have shown promising application prospects in the fields of renewable energy and electric vehicles due to their high safety and environmental friendliness. However, the structural instability of aqueous electrolytes seriously affects their electrochemical performance under a wide temperature range. In this study, a high-entropy electrolyte, Li₂ZnBr₄·9H₂O (HEE), is constructed by introducing LiBr as a supporting salt into the ZnBr₂ aqueous electrolyte. In this high-entropy electrolyte, due to the Lewis acid–base characteristics of bromide ions, they tend to exclude water molecules from the solvation structures, forming [ZnBr_4−m^2−m]_n anionic clusters. Meanwhile, the partially hydrated Li–Br structure not only disrupts the hydrogen bonding network but also breaks up the [ZnBr_4−m^2−m]_n clusters, allowing them to exist in the form of short aggregates (n ≤ 3), which significantly improves the low-temperature stability and ionic conductivity of the high-entropy electrolyte. Therefore, the Zn‖Cu batteries based on HEE electrolyte exhibit an ultralong cycle life of 1200 cycles with an average coulombic efficiency of 99.7% at a current density of 0.5 mA cm⁻² at 30 °C. The Zn‖NVO batteries based on HEE electrolyte display a high capacity retention of 85.2% after 5000 cycles at 30 °C. Furthermore, when the temperature is reduced to −30 °C, the Zn‖NVO batteries display a high capacity retention of 71.2% after 800 cycles. This design strategy may provide strong support for the further optimization and design of ZIBs.