Solvation Structures in Aqueous Metal‐Ion Batteries

Abstract Aqueous batteries have attracted great attention due to their inherent low cost, intrinsic safety, and environmental friendliness. Because of intrinsic oxygen evolution reactions (OER) and hydrogen evolution reactions (HER) via water splitting, aqueous batteries possess narrow electrochemical stability windows (ESWs, theoretical ESW is 1.23 V), leading to low output voltage and low delivered capacity, and thus low energy density. Meanwhile, the parasitic side reactions of electrode materials dissolution, gas evolution, and dendrite growth can shorten cyclic stability of aqueous batteries. The above deep‐seated challenges are closely related to the solvation structure of metal ions, which can be settled by adjusting and regulating the solvation structure. This review summarizes the research progress in solvation structures in metal‐ion batteries. First, the design principles of the solvation structure and its impact on battery performance are introduced. Second, the regulation of the solvation structure and the research progress are introduced from three points of view: high concentration salt strategies, MOF modification and electrolyte additives. After that, the commonly used characterization methods for solvation structure are summarized. Finally, the existing problems and challenges in the frontier research of solvation structure research are summarized.