Pioneering the Future: Principles, Advances, and Challenges in Organic Electrodes for Aqueous Ammonium-Ion Batteries

Aqueous ammonium-ion (NH₄ ⁺) batteries (AAIBs) have recently been considered as attractive alternatives for next-generation large-scale energy storage systems, on account of their cost-effectiveness, nonflammability, less corrosive, small hydrated ionic radius, and rapid NH₄ ⁺ diffusion kinetics. In addition, the tetrahedral structure of NH₄ ⁺ exhibits preferential orientation characteristics, resulting in a different electrochemical storage mechanism from spherical charge carriers such as Li⁺, Na⁺, and K⁺. Therefore, unlocking the NH₄ ⁺-ion storage mechanisms in host electrode materials is pivotal to advancing the design of high-performance AAIBs. Organic materials, with their customizable, flexible, and stable molecular structures, along with their ease of recycling and disposal, offer tremendous potential. However, the development of cutting-edge organic electrode materials specifically for ammonium-ion storage in AAIBs remains an exciting, yet largely untapped, frontier. This review systematically explores the interaction mechanisms between NH₄ ⁺ ions and organic electrode materials, such as electrostatic interactions including hydrogen bonding. It also highlights the application of diverse organic electrode materials, such as small molecules, conducting polymers, covalent organic frameworks (COFs), and organic-inorganic hybrids in AAIBs. Lastly, the review addresses the key challenges and future perspectives of organic-material-based AAIBs, aiming to push the boundaries of cutting-edge aqueous energy storage systems.