Advanced polyanionic cathode materials for aqueous zinc-ion batteries: from crystal structures, reaction mechanisms, design strategies to future perspectives

Abstract

Aqueous zinc-ion batteries (AZIBs) are promising contenders for large-scale energy storage systems (ESSs) due to their high security, high capacity, low cost, and ecological friendliness. Polyanionic materials have been extensively investigated as promising cathodes for AZIBs by virtue of their high operating voltages and robust structures in recent years. Nevertheless, their poor intrinsic electronic conductivity, relatively low specific capacity, and complex and controversial energy storage mechanisms still hinder their development. Herein, aiming at tackling these challenging issues, we comprehensively review the latest research progress in polyanionic cathode materials for AZIBs. First, we summarize the three typical crystal structures of polyanionic compounds, including Na superionic conductor (NASICON)-type, layered, and olivine-type structures. Next, we discuss the three mainstream fundamental reaction mechanisms of Zn²⁺ insertion/extraction, ion/molecule co-insertion/extraction, and anionic redox chemistry. Then, we expound four feasible design strategies: intercalation engineering, defect/doping engineering, morphology control, and surface coating. Finally, the critical remaining challenges and future perspectives on advanced polyanionic cathode materials for aqueous Zn-storage are elaborated. We believe that this review can provide novel insights into the development of high-performance polyanionic cathode materials for AZIBs.