Strategies of regulating Zn²⁺ solvation structures for dendrite-free and side reaction-suppressed zinc-ion batteries

High-safety and low-cost aqueous zinc-ion batteries (ZIBs) are an exceptionally compelling technology for grid-scale energy storage, whereas the corrosion, hydrogen evolution reaction and dendrite growth of Zn anodes hamper their further development, which are derived from the decomposition of active water molecules belonging to Zn²⁺ solvation structures in electrolytes. In recent years, strategies of regulating Zn²⁺ solvation shells in electrolytes have been demonstrated to effectively suppress the above-mentioned issues, and fruitful achievements have been made. However, there is a lack of systematic summary on the functional mechanisms and solvation structure evolution of electrolytes or electrolyte additives. Herein, this review gives a comprehensive introduction of the solvation structure regulation strategies based on electrolyte engineering for dendrite-free and side reaction-suppressed ZIBs, including high-concentration electrolytes, deep eutectic solvents, ionic liquids, functional additives, solid-state electrolytes and super-saturated electrolyte layers, particularly an in-depth and fundamental understanding of the effects and mechanisms of electrolyte modification on Zn²⁺ solvation shells. Furthermore, the general performance metrics of the above-mentioned strategies, potential directions and perspectives for further research are proposed.