Although it is pretty clear that a typical metal-ion capacitor has the privilege of using both the electrochemical capacitor technology (due to the EDLC component as one of the electrodes) and metal-ion-based battery electrode, the working mechanism of the overall system could, in fact, be a lot trickier than it might appear to us.
Sodium-ion capacitors (SICs) can offer cost and resource configuration advantages compared to lithium-ion capacitors (LICs). By virtue of the strong redox reaction, metal oxide electrodes have the potential to achieve a higher theoretical specific capacity than traditional carbon-based electrodes, making them potential candidates for SICs.
To compete with monovalent metal-ion capacitors, in terms of energy density, multivalent metal systems should be employed in their pure metallic form as one of the electrodes. This is an essential parameter for achieving highest possible energy density values from these multivalent metal-ion-based energy storage systems.
As metal-ion capacitors are energy storage devices, their performance evaluation, therefore, should be done from their charge–discharge profile. This can be done through galvanostatic charge–discharge technique. In fact, this galvanostatic technique can be used to optimize the working potential window of an electrochemical system.
This is the reason why among all the discussed metal ions, zinc has the utmost potential to be used as a low-cost and environmentally friendly electrode material for metal-ion capacitors. Much of the chemistries involving zinc are restricted to non-rechargeable systems such as alkaline zinc batteries, zinc-air batteries, etc.
Summary and outlook Metal-ion hybrid capacitors (MIHCs), recognized for their high energy power density and long cycle life, have undergone substantial advancements since their inception. The electrochemical performance of MIHCs is highly dependent on the properties of electrode materials.