A Biomimetic Bidirectional Interphase Enabled by a Single Molecule for Ultra‐Stable Zn‐I 2 Batteries

ABSTRACT Though zinc‐iodine (Zn‐I 2 ) batteries hold considerable promise for grid‐scale energy storage, their development remains constrained by zinc dendrite formation, detrimental side reactions, and polyiodide shuttle. In this work, sodium camphorsulfonate (SCS) is introduced as a biomimetic bidirectional electrolyte additive to simultaneously address these issues. At the anode, SCS participates in the Zn 2 + solvation to suppress HER, while its preferential adsorption on Zn anode guides the dendritefree (002) plane. At the cathode, the SCS exhibits strong binding affinity toward I 2 , effectively inhibiting polyiodide shuttle. Moreover, the adsorbed SCS layer on Zn acts as a barrier against migrating polyiodides, mitigating Zn anode interfacial corrosion. Thus, the Zn||Zn symmetric cell with 10 SCS/BE demonstrates ultra‐stable cycling for 1449 h at 5 mA cm − 2 /5 mAh cm − 2 . The Zn‐I 2 full cell retains 154.0 mAh g − 1 capacity after 26 000 cycles at 5 A g − 1 . The corresponding pouch battery with a 20 µm Zn foil and a high iodide loading (10.5 mg cm − 2 ) cathode displays a capacity of 175.1 mAh g − 1 after 500 cycles at 0.5 A g − 1 . This work provides a cost‐effective design strategy for stabilizing both electrodes in Zn‐I 2 batteries through a single molecular additive and guarantee a durable cyclic performance of Zn‐I 2 batteries.