Boosting the Cycling Stability of Manganese Prussian Blue Analogs by Cu‐Substitution and Water Reduction for Sodium‐Ion Batteries

Manganese‐based Prussian blue analog (MnPBA) shows great potential as a high energy density and low‐cost cathode material for sodium‐ion batteries (SIBs) due to its electrochemical activity, high redox potential, low‐cost raw materials, and facile synthesis. However, its practical application is severely challenged by the high water content (>10 wt%) in the framework and the Jahn–Teller effect from high‐spin Mn 3+ , leading to poor reversibility and rapid capacity decay during cycling. Herein, Cu‐substituted MnPBA samples (CuMnPBAs) are successfully synthesized under high‐concentration chelation conditions, which reduced the water content and alleviated the Jahn–Teller effect from Mn 3+ . Accordingly, the optimal 25% Cu‐substituted MnPBA (CuMnPBA‐25) exhibits a significantly reduced water content of 7.6% and excellent cyclability, maintaining 81.2 mAh g −1 at 1 C after 700 cycles. Furthermore, the CuMnPBA‐25/hard carbon (HC) pouch cell exhibits superb capacity retention of 80.9% after 280 cycles. This research provides new insights into the development of highly stable PBAs for practical applications in SIBs.