Advanced ammonium salt materials for electrochemical energy storage: Recent progress and future perspectives

Abstract

The development of new high-performance materials is essential for robust electrochemical energy storage (EES). In recent years, ammonium salt materials, as an emerging class of layered materials, have attracted considerable attention as electrode materials for EES due to their abundant resources, simple synthesis, low cost, and high specific capacity. This review aims to comprehensively summarize the recent progress of ammonium salt materials for EES. Firstly, the crystal structures and preparation methods of typical ammonium salts including ammonium vanadate, ammonium metal phosphate, and ammonium metal molybdate are discussed. Subsequently, their application for supercapacitors (SCs) and various metal-ion batteries including monovalent alkali ion (Li+, Na+, and K+), ammonium ion (NH4+) batteries, zinc ion (Zn2+) batteries, and multivalent alkali-earth ion (Mg2+ and Ca2+) batteries is thoroughly introduced. Likewise, the structure–activity relationships between the layered structure of ammonium salts and their electrochemical performance are clarified. In particular, diverse modification strategies including composites, defect, and doping engineering for ammonium salt materials as electrode materials for Zn-ion batteries are presented. Thereafter, various advanced characterization techniques together with theoretical calculations are expounded to further explain the internal structure evolution and reaction mechanism of ammonium salt materials for EES. Finally, a short conclusion and outlook, along with the current challenges and future opportunities of ammonium salts for EES, are proposed.