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 VOPO<inf>4</inf>·2H<inf>2</inf>O (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 NH<inf>4</inf>⁺ 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.