Tailoring high‐concentration aqueous electrolytes for enhanced anion intercalation behavior in dual‐ion batteries

Abstract Aqueous dual‐ion batteries (ADIBs) are promising for large‐scale storage but face challenges in a lack of in‐depth understanding of anion intercalation behavior and the difficulty in formulating aqueous electrolytes with a wide electrochemical stability window. Here, we regulate the anion intercalation behavior in graphite cathodes by designing high‐concentration aqueous electrolytes using organic lithium salts (LiTFSI, LiFSI, and LiOTf). A combined experimental and theoretical calculation reveals that the intercalation behavior, including intercalation energy and diffusion barrier, is highly anion‐dependent, identifying TFSI − and FSI − as the anions with the most favorable kinetics and reversibility. Electrolyte optimization, particularly a mixed‐salt system (37m 9LiFSI‐1LiTFSI), expands the electrochemical window beyond 3.1 V and enhances cycling stability. Furthermore, partial water substitution by 12‐crown‐4 ether effectively suppresses hydrogen evolution, boosting the Coulombic efficiency to 90%. This work provides fundamental insights into anion intercalation mechanisms in aqueous media and offers a viable electrolyte design strategy toward high‐voltage ADIBs.