Zn‐Ion Storage in an Anode‐Protected High‐Performance Aqueous Organic Zinc Ion Battery

ABSTRACT In this work, we discuss the complexities of Zn 2+ ‐ion storage in an organic stacked layered naphthalenediimide (NDI) via systematic experimentation and theoretical calculations. Apart from the possibility of insertion/deinsertion, NDI also provides redox‐active docking motifs for Zn 2+ ‐ions. Additionally, the anode‐associated challenges are mitigated using zinc phthalocyanine (ZnPc) as an organometallic protective layer. Despite achieving a high coulombic efficiency (>99%) at high cycle numbers, capacity degradation is observed during long‐term cycling. The observed capacity fade is attributed to the underlying NDI's transformation from a hexagonal to a flower‐like morphology. This structural evolution is attributed to the co‐insertion of Zn 2+ and protons from the electrode/electrolyte interface into the bulk cathode via coordination with carbonyl (─CO) and amine (─NH 2 ) groups. Additionally, the capacity fade is attributed to the sluggish kinetics of Zn 2+ stripping/plating. The ZnPc protective layer effectively guides Zn 2+ deposition along the (002) crystal plane, suppresses side reactions, and enhances both the capacity retention and cycling stability of the battery. Accounting for Zn 2+ ‐ion storage in a redox‐active organic host through the elucidation of key roles in phase transitions, ion diffusion dynamics, and zinc electrodeposition/dissolution processes provides a deep‐dive conceptual framework for designing novel organic Zn 2+ ‐ion hosts for practical AZIBs.