Ammonium‐Anchored Mn‐Based Prussian Blue Analogues via Hydrogen Bonding for Robust Sodim‐Ion Battery Cathodes

ABSTRACT Manganese‐based Prussian blue analogues (Mn‐PBAs) are promising sodium‐ion battery (SIB) cathodes due to their low cost and high operating voltage. However, their practical application is hindered by structural degradation, including Jahn‐Teller distortion, Mn dissolution, and an irreversible cubic‑to‑tetragonal phase transition, which collectively drive rapid capacity fade. Here, we report a hydrogen‐bond anchoring strategy in which tetrahedral ammonium (NH ₄ ⁺ ) ions are incorporated into the A‐site cavities of manganese hexacyanoferrate (MnHCF) to establish framework‐stabilizing N─H···N hydrogen‐bond interactions with cyanide ligands. This molecular‐level reinforcement suppresses Jahn‐Teller distortion, prevents the irreversible cubic‑to‑tetragonal transition during deep desodiation, and mitigates particle cracking, thereby enhancing structural reversibility. The NH ₄ ⁺ ‐anchored MnHCF (A‐MnHCF) delivers long‐term durability, retaining ∼88% of its initial capacity after 1000 cycles at 1 C. In‑situ XRD, FT‐IR, and XPS demonstrate that NH ₄ ⁺ remains within the framework and that N─H···N hydrogen bonding persists throughout cycling, corroborating the stabilization mechanism. This work establishes hydrogen‐bond anchoring as a general paradigm for stabilizing Mn‐based PBAs, paving the way for long‐life, low‐cost SIBs suitable for grid‐scale energy storage.