Electrochemical Zinc Ion Capacitors: Fundamentals, Materials, and Systems

An electrochemical zinc ion capacitor (ZIC) is a hybrid supercapacitor composed of a porous carbon cathode and a zinc anode. Based on the low-cost features of carbon and zinc metal, ZIC is a potential candidate for safe, high-power, and low-cost energy storage applications. ZICs have gained tremendous attention in recent years. However, the low energy densities and limited cycling stability are still major challenges for developing high-performance ZICs. First, the energy density of ZIC is limited by the low capacitance of porous carbon cathodes. Second, aqueous electrolytes induce parasitic reactions, which results in limited voltage windows and poor cycling performances of ZICs. Third, the poor stabilities and low utilization of zinc anodes remain major challenges to develop practical ZICs. This review summarizes the recent progress in developing ZICs and highlights both the promising and challenging attributes of this emerging energy storage technology. Future research directions are proposed for developing better, lower cost, and more scalable ZICs for energy storage applications.