Ammonium-ion energy storage devices for real-life deployment: storage mechanism, electrode design and system integration

Abstract

In recent times, there has been growing interest among researchers in aqueous energy storage devices that utilize non-metallic ammonium ions (NH₄⁺) as charge carriers. However, the selection of suitable materials for ammonium storage presents significant challenges. The understanding of the energy storage mechanism in electrodes for ammonium ion-based devices remains limited, which hampers the development of the corresponding modification techniques. Based on the previous research in the field of ammonium-ion energy storage devices, this review aims to provide the first comprehensive insight into ammonium-ion energy storage systems, from individual electrode materials to the overall design of devices, for real-world deployment. First, the review delves into the energy storage mechanisms of NH₄⁺ in depth, encompassing processes such as NH₄⁺ intercalation/de-intercalation, NH₄⁺/H⁺ co-insertion/extraction, adsorption/desorption, and conversion reactions. Then, critical evaluation of electrode design strategies is presented, with emphasis on leveraging large framework features, selecting organic substances with specific functional groups, fabricating amorphous structures, achieving ionic/molecular intercalation, adjusting structural water, constructing composite materials, and regulating defective structures. Furthermore, the review discusses optimization approaches for integrated devices, including electrolyte modification, use of advanced substrates, the development of multifunctional devices, and the utilization of hybrid-ion/dual-ion batteries. Finally, the review analyzes potential challenges and future perspectives for aqueous ammonium-ion energy storage devices. This review will pave the way to next-generation ammonium ion storage systems from fundamental science breakthroughs, practical prototypes and eventually to real-life deployment and commercialization.