Structural Disorder‐Order Transition Driven by Valence Variation: Iodine Trapping via a Chemo‐Physical Synergistic Approach for High‐Performance Sodium‐Iodine Batteries

ABSTRACT To avoid iodine dissolution in electrolytes and the resultant shuttle effect in Na‐I ₂ batteries, a chemo‐physical synergistic strategy for iodine immobilization is proposed based on a 3D porous compound formulated as Cu ₃ (OH) ₂ V ₂ O ₇ ·2H ₂ O (CuVO). After low‐temperature annealing, the dehydrated sample, D‐CuVO, becomes amorphous, but maintains the original host skeleton. After H ₂ O ₂ ‐treatment, D‐CuVO recovers to the crystalline phase, and the order‐disorder conversion is associated with valence variation. After incorporation of iodine, CuI is detected in D‐CuVO@I ₂ , and the cycled D‐CuVO@I ₂ can restore to the original crystalline D‐CuVO after H ₂ O ₂ ‐treatment, indicating the reversible transformation of D‐CuVO + 1/2 I ₂ ↔ CuI + Cu‐deficient D‐CuVO during cycling. This is related to abundant Cu–O–Cu linkages and short Cu ··· Cu distances in D‐CuVO, which can stabilize the framework of D‐CuVO in the presence of a Cu defect. Furthermore, I ⁻ can be reversibly adsorbed/desorbed on the CuI (111) surface. Additionally, a new NaVO ₃ host phase appears in the discharge process, which originates from partial irreversible intercalation of Na ⁺ into D‐CuVO. The inner channel of the NaVO ₃ host phase can physically accommodate iodine. D‐CuVO@I ₂ shows excellent electrochemical performance in Na‐I ₂ batteries.