Dual‐Ion Cl ⁻ /Zn ²⁺ Storage in a π‐Conjugated Indanthrone Cathode for Aqueous Zinc Batteries

Conventional aqueous zinc batteries rely almost exclusively on Zn 2+ insertion reactions, limiting reaction diversity and often causing structural instability. Here we show that a π‐conjugated indanthrone molecular crystal enables an unusual dual‐ion Cl − /Zn 2+ storage mechanism in aqueous electrolyte. The IDT lattice combines carbonyl redox sites with π‐stacked channels that allow anion interaction within the conjugated framework. Electrochemical and spectroscopic analyses reveal that Zn 2+ coordinates with carbonyl oxygen sites during discharge in the low‐voltage region (0.4–1.4 V), while oxidation at higher potentials (1.6–1.8 V) is compensated by reversible uptake of Cl − within the π‐conjugated lattice. Ex situ XRD, Raman, and XPS measurements consistently support this direction‐dependent ion participation. The IDT framework undergoes only small and reversible lattice variations during cycling, enabling stable operation in aqueous electrolytes. This work establishes a molecular‐crystal strategy for enabling cation‐anion coupled storage in aqueous batteries, expanding the reaction chemistry of zinc systems beyond conventional Zn 2+ ‐dominated insertion mechanisms.