Triple Active Sites in Prussian Blue Analogues for High‐Capacity Aqueous and Seawater Ammonium Ion Batteries

ABSTRACT Aqueous ammonium‐ion battery has recently gained attention as a safe, high‐power, and cost‐effective energy storage device; yet the development in cathode materials that can simultaneously deliver high capacity, high potential, and stable cycling performance is limited. Herein, a Prussian blue analog with three redox‐active sites (Co, Mn, and Fe) as a high‐performance cathode material for aqueous ammonium‐ion batteries by a dual function doping strategy is reported. It achieves a high reversible capacity of 153 mAh g −1 and superior cycling stability over 2500 cycles with negligible capacity decay. Density functional theory calculations and electrochemical analysis reveal that Mn activates the redox activity of Co via the enhanced electron depletion, while Co effectively suppresses the Jahn–Teller effect through splitting the degenerate orbitals of Mn, preserving the long‐range structural integrity of the framework. Paring this cathode with the VO x @polypyrrole anode, a high specific energy of 145.7 Wh kg −1 can be achieved at a high specific power of 810.9 W kg −1 . This work offers a viable design strategy for the optimization of electrode materials through unlocking multiple active sites and stabilizing lattice frameworks.