Unlocking High‐Performance Ammonium‐Ion Batteries: Activation of In‐Layer Channels for Enhanced Ion Storage and Migration

Abstract Ammonium‐ion batteries, leveraging non‐metallic ammonium ions, have arisen as a promising electrochemical energy storage system; however, their advancement has been hindered by the scarcity of high‐performance ammonium‐ion storage materials. In this study, an electrochemical phase transformation approach is proposed for the in situ synthesis of layered VOPO₄·2H₂O (E‐VOPO) with predominant growth on the (200) plane, corresponding to the tetragonal channels on the (001) layers. The findings reveal that these tetragonal in‐layer channels not only furnish NH₄⁺ storage sites but also enhance transfer kinetics by providing rapid cross‐layer migration pathways. This crucial aspect has been largely overlooked in previous studies. The E‐VOPO electrode exhibits exceptional ammonium‐ion storage performance, including significantly increased specific capacity, enhanced rate capability, and robust cycling stability. The resulting full cell can be stably operated for 12 500 charge–discharge cycles at 2 A g⁻¹ for over 70 days. The proposed approach offers a new strategy for meticulously engineering electrode materials with facilitated ion storage and migration, thereby paving the way for developing more efficient and sustainable energy storage systems.