Aqueous ammonium ion battery (AAIB) is a new type of energy storage device with non-metallic ion (NH4+) as the carrier, possessing the apparent advantages of low cost, high safety, and long-term sustainability. However, the sluggish kinetics of the electrolyte-electrode interface often results in a slow NH4+ transport within the host structure, leading to poor cycling stability, especially in the type of cathode material with open frameworks represented by Fe-based Prussian blue analogues (PBAs). In this work, a NiFe-PBA (NiFe) cathode material with asymmetric bimetallic sites is purposely designed to regulate and improve the NH4+ desolvation kinetics at the electrolyte-electrode interface. Theoretical simulations first reveal that regulating the asymmetric bimetallic site effectively reduces the energy barrier of NH4+(H2O)4 desolvation at the electrolyte-electrode interface, and thus the NH4+(H2O)4 can be desolvated into NH4+ into host material. The electrochemical study results further show that the successful introduction of asymmetric bimetallic sites largely improves the diffusion kinetics and structural stability of FeFe-PBA (FeFe), realizing stable cycling performance (97 % retention after 700 cycles at 0.25 A g−1) and high-rate capability. Finally, in-situ characterizations in combination with theoretical calculations demonstrate that the insertion/extraction of NH4+ is attributed to the charge storage mechanism of reversible interactions in association with the coordination of N atoms in the NiFe-PBA.