Zinc-compound iodine battery chemistry with dual functional oxalate-based electrolyte

Aqueous Iodine-based batteries represent great promising for safe and low-cost energy storage system. However, traditional zinc metal iodine batteries suffer from self-discharge (polyiodide shuttle to the zinc anode) and low operating voltage ( vs. Zn 2+ /Zn). Herein, a novel zinc-compound (ZnC 2 O 4 ·2H 2 O, ZCO) iodine battery chemistry based on dual functional K 2 C 2 O 4 electrolyte was first proposed in response to these challenges. The C 2 O 4 2− , characterized by its exceptionally low solubility with zinc cations, effectively induces a transition in zinc deposition behaviour from a liquid-to-solid to a solid-to-solid mechanism, thereby significantly enhancing the cell’s voltage output. Meanwhile, the lone-pair electrons of the C 2 O 4 2− engage in strong donor/acceptor interactions with the vacant σ * orbitals of I 2 and I 3 − , resulting in the formation of stable electronic coordination structures and the suppression of polyiodide generation and shuttle. Therefore, the ZCO-I 2 full cell has excellent cycling stability over 2000 cycles and impressive Coulombic efficiency of 99.8%. This work provides a new perspective for novel conversion-type anode/electrolyte engineering and mechanism innovation in aqueous iodine-based battery systems. The introduction of a ZnC 2 O 4 ·2H 2 O (ZCO) anode paired with a dual-functional K 2 C 2 O 4 electrolyte reshapes iodine-based battery chemistry, shifting zinc deposition from liquid-to-solid to efficient solid-to-solid and boosting voltage. Competitive coordination enables dual storage, while oxalate tethers iodine species to suppress shuttling. The ZCO–I 2 cell delivers 184 mAh g −1 and exceptional cycling stability exceeding 2000 cycles.