Transition Metal Oxide-Based Aqueous Zinc Ion Hybrid Supercapacitors: A Review

Abstract

Transition metal oxide (TMO)-based aqueous zinc-ion hybrid supercapacitors (ZIHSCs) have emerged as promising next-generation energy-storage systems that bridge the gap between batteries and supercapacitors by combining the high energy-storage capability of battery-type Zn anodes with the rapid charge–discharge characteristics of capacitor-type or pseudocapacitive cathodes. Their intrinsic safety, environmental compatibility, and enhanced electrochemical performance make them promising alternatives for advanced energy-storage applications. TMOs are widely investigated as cathode materials owing to their multiple oxidation states, rich redox activity, structural tunability, natural abundance, and high theoretical capacitance. However, their practical application remains constrained by poor electrical conductivity, structural instability, active-material dissolution, and sluggish Zn²⁺ diffusion kinetics. This review systematically summarizes recent advances in TMO-based aqueous ZIHSCs, covering device configurations, Zn²⁺ storage fundamentals, and charge-storage mechanisms, particularly emphasizing on rational cathode design strategies, including nanostructure engineering, defect and vacancy modulation, and composite integration, to improve electrochemical performance. Furthermore, electrochemical charge-storage mechanisms, Zn²⁺ intercalation/deposition behavior, electrolyte optimization, and interfacial reaction kinetics are critically discussed. Finally, key challenges, including Zn dendrite growth, cathode degradation, and electrolyte instability, are highlighted, and future research directions are proposed. This review provides a comprehensive perspective and strategic framework for developing high-performance TMO-based aqueous ZIHSCs for next-generation energy-storage applications.