Boosting Performance of Aqueous Ammonium Ion Batteries via Mn-Partial-Substituted Cu Prussian Blue Cathode

Aqueous ammonium ion batteries (AAIBs) represent a highly promising alternative for large-scale energy storage. Prussian blue analogues (PBAs) offer advantages such as higher operating voltages and a robust three-dimensional open framework, highlighting their potential as a cathode. However, the practical implementation of PBAs is constrained by their inherent limitations, namely, low specific capacity and insufficient cycling durability. Herein, Mn-partially substituted Cu-based PBA, MnCu-PBA, was fabricated via a coprecipitation method. Consequently, the MnCu-PBA cathode exhibited a high specific capacity, favorable rate capability, and outstanding cycling stability. Furthermore, ex-situ characterizations confirm the highly reversible redox activity of the Fe, Cu, and Mn centers within the MnCu-PBA structure. A full AAIB of MnCu-PBA//BPD delivered a specific capacity of 61 mAh g–1 (based on the total active mass of both electrodes) and extended cycle life over 4000 cycles with 95.2% capacity retention. This work provides a novel perspective for designing PBAs with advanced performance for AAIBs.