Charge Storage Mechanisms and Material Design of Ammonium Ion Batteries

Aqueous ammonium‐ion batteries (AAIBs) have emerged as a compelling alternative for large‐scale energy storage due to the abundance, safety, and unique chemistry of NH 4 + charge carriers. However, the commercialization of AAIBs is hindered by significant challenges, including the severe structural strain induced by the bulky NH 4 + ion and the restricted electrochemical stability window of aqueous electrolytes that leads to undesired side reactions. This review provides a systematic overview of the recent progress in AAIBs, focusing on the fundamental charge storage mechanisms and advanced material design strategies. This review categorize and evaluate key electrode materials, including Prussian blue analogs, transition metal oxides, and organic compounds, emphasizing how modification strategy can accommodate the large NH 4 + ions to enhance cycling stability. Furthermore, we discuss the evolution of electrolyte systems from dilute solutions to highly concentrated “Water‐in‐Salt” electrolytes as a means to suppress water splitting and expand operating voltages. This review concludes that the unique tetrahedral geometry and hydrogen‐bonding of NH 4 + are central to designing high‐performance electrodes and electrolytes. These insights provide a clear roadmap for transitioning AAIBs from fundamental research to practical, large‐scale energy storage applications.