Formation of CuMn Prussian Blue Analog Double‐Shelled Nanoboxes Toward Long‐Life Zn‐ion Batteries

Prussian blue analogs (PBAs) are promising candidates for aqueous Zn-ion batteries due to their unique open-framework structures. However, they suffer from limited capacity and severe capacity decay originating from insufficient redox sites and structural instability. Herein, Cu-substituted Mn-PBA double-shelled nanoboxes (CuMn-PBA DSNBs) prepared by tannic acid etching and cation exchange approaches are demonstrated for efficient Zn ion storage. The unique hollow structures can expose abundant active sites and alleviate the volume change during the cycling test. Moreover, partial Cu substitution and induced Mn vacancies might inhibit the Jahn-Teller distortions of Mn-N6 octahedra, thus contributing to the prolonged lifespan. As a result, CuMn-PBA DSNBs exhibit high reversible capacity, decent rate performance and superior cycling stability for 2000 cycles. Furthermore, ex situ characterizations reveal that the charge storage mechanism of CuMn-PBA DSNBs mainly involves the reversible redox reactions of transition metals and Zn2+ ion insertion/extraction processes.