General overview of sodium, potassium, and zinc-ion capacitors

In recent years metal ion capacitors (MICs) and supercapacitors devices have been reported as promising alternatives for energy storage on a large scale. MICs are characterized by superior power density and energy density, combining advantages of metal-ion batteries such as lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, zinc-ion batteries, etc., and those of supercapacitors. Herein we provide a review of recent progress on MICs, focusing on the sodium-ion capacitor (SICs), potassium-ion capacitors (PICs), and zinc-ion capacitors (ZICs); starting from the basic concepts (the perspectives of the design concepts, the configuration of MICs devices, the electrochemical behavior and the energy storage mechanism), the electrode materials and electrolyte systems in details with some examples. The factors impacting the electrochemical performances of the MICs are also provided in this work and end with a conclusion. This review will be helpful for researchers, especially the new researchers in the field of MICs and supercapacitors, to have an overall understanding of MICs and supercapacitors, develop electrochemical storage devices, and respond to the need forenergy storage in electric vehicles and electronic devices.