Dual‐Cation Batteries via Synergistic Cation‐Sieving Electrodes and Tailored Electrolytes

ABSTRACT This study presents a dual‐cation battery enabled by electrolyte engineering and cation‐sieving electrodes. The design leverages the high capacity, low working potential, and stable cycling performance of Li + intercalation in the graphite anode along with the high discharge voltage, fast kinetics, and low cost of K + storage in the K 2 Mn[Fe(CN) 6 ] cathode. The proposed hybrid electrolyte promotes Li + ‐anion aggregations and preferential decomposition, producing a Li‐dominant solid electrolyte interphase that suppresses K + intercalation at the anode. Simultaneously, it reduces the number of highly coordinated K + , lowers the desolvation barrier, and facilitates charge transfer, thus enhancing the K + insertion kinetics at the cathode. As a result, the designed dual‐cation cell delivers an average discharge voltage of 3.80 V, a specific energy of 336.7 Wh kg −1 (based on total mass of graphite and K 2 Mn[Fe(CN) 6 ]), 72.5% of capacity obtained at 20 C discharge rate, and 80% capacity retention after 1200 cycles at 3 C. This synergistic electrolyte‐electrode strategy not only overcomes key challenges in hybrid‐ion battery design but also establishes a mechanistic framework for designing cost‐effective, high‐performance dual‐cation energy storage systems.