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

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.