Advances in aqueous dual-ion batteries: Anion storage mechanisms, challenges and electrolyte design

Aqueous dual-ion batteries (ADIBs) represent an innovative energy storage system utilizing dual-ion (anion/cation) charge carriers. These systems exhibit inherent safety, environmental benignity, economic viability, and rapid reaction kinetics, demonstrating significant potential for large-scale energy storage applications. Nevertheless, the intricate anion storage mechanisms, coupled with a range of critical challenges arising from the constrained electrochemical stability window (ESW) of aqueous media, electrode-associated parasitic reactions, the low specific capacity or operating voltage of cathode materials, and dramatic volume changes, pose significant obstacles to their practical application. This review explores the mechanisms of anion storage, the challenges faced, and the design of electrolytes in ADIBs. It elucidates anion storage pathways, including intercalation/deintercalation, coordination/dissociation, conversion reactions, conversion-intercalation, and analyzes limitations such as the narrow ESW, unsatisfactory coulombic efficiency, limited energy density, and poor cycling performance. Strategies for electrolyte design to enhance ADIBs performance are discussed with emphasis on the impact of electrolyte composition on solvation structures, hydrogen-bond networks, insertion potential, and the electrode-electrolyte interface. The review concludes with personal insights into ADIBs development, offering a roadmap for advancing anion reaction chemistry and electrolyte optimization in future research endeavors. © 2025 Elsevier B.V.