Dual-Ion Cl^-/Zn²⁺ Storage in a π-Conjugated Indanthrone Cathode for Aqueous Zinc Batteries

Conventional aqueous zinc batteries rely almost exclusively on Zn²⁺ 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^-/Zn²⁺ 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 Zn²⁺ 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 Zn²⁺-dominated insertion mechanisms.