Reversible Chlorine Storage in Li/Na-Cl 2 Batteries via the Open Framework of Fe-based Prussian Blue Analogue

Rechargeable Li‑Cl 2 and Na‑Cl 2 batteries are regarded as promising high‑energy‑density energy‑storage candidates owing to their appealing conversion electrochemistry between chlorine and alkali‑metal chlorides. Nevertheless, practical deployment is greatly hindered by the shortage of reliable cathode host materials that can reversibly confine chlorine‑related species and mitigate parasitic side reactions. Carbon materials and organic frameworks (MOFs/COFs) have been extensively investigated as chlorine hosts, whereas inorganic coordination host materials remain largely unexplored for metal‑chlorine battery systems. Herein, we report an iron‑based Prussian blue analogue (Fe‑PBA) with an open monoclinic coordination framework as a new‑type cathode host for both Na‑Cl 2 and Li‑Cl 2 batteries. Prepared via a facile coprecipitation route, Fe‑PBA possesses interconnected 3D cavities that accommodate chlorine intermediates and facilitate ion transport. When applied in Na‑Cl 2 batteries, Fe‑PBA delivers stable cycling over 160 cycles, superior rate capability up to 3000 mA g -1 , and a large reversible capacity reaching 1434 mAh g -1 . Comparable electrochemical improvements are also realized in Li‑Cl 2 configurations. Combined ex‑situ EIS‑DRT and XPS characterizations verify reversible Cl 2 ‑chloride conversion within Fe‑PBA cavities and confirm the structural robustness of the Fe‑CN framework upon repeated cycling. This work expands the library of host materials for metal‑chlorine batteries and demonstrates the great potential of inorganic Prussian‑blue‑analogue coordination frameworks toward high‑performance chlorine‑storage energy‑storage devices.