Tailoring surface structures in Mn-based Prussian blue analogues for enhanced NH₄⁺ transport and high-performance aqueous batteries

Aqueous ammonium-ion batteries (AAIBs) have attracted significant attention, with Prussian blue analogues (PBAs) emerging as promising cathode materials. Although Mn-PBA possesses multiple redox-active centers and high specific capacity in AAIBs, its limited structural stability and inadequate utilization of active sites continue to hinder its broader application. In this work, a novel, direct, and efficient strategy utilizing tannic acid (TA) is employed to achieve omnidirectional modulation of Mn-PBA, leading to the full exposure of active sites within the Mn-PBA-TA framework. As a result, the Mn-PBA-TA cathode exhibits a reversible specific capacity of 120.3 mAh g^-1 after 200 cycles at 1 A g^-1, demonstrating high active site availability. Furthermore, it retains exceptional cycling stability over 10 000 cycles at a current density of 15 A g^-1, with an ultra-low capacity fade of just 0.0036% per cycle. A comprehensive investigation into the NH₄⁺ electrochemical diffusion behavior, redox capability, and structural stability of Mn-PBA-TA is conducted, complemented by theoretical calculations that elucidate a rational NH₄⁺ migration pathway and its associated energy barriers. Based on these insights, a full cell assembled with a quinone-imine organic anode delivers a high-power density output. This study provides valuable insights into the chemical modification of PBAs, paving the way for the development of advanced cathodes in aqueous batteries.