Advances in Lithium‐Ion and Sodium‐Ion‐Based Supercapacitors: Prospects and Challenges

Among the emerging renewable and sustainable energy technologies, supercapacitors (SCs) are considered as the most prominent energy conversion and storage tool, thanks to their outstanding power and longer lifespan. However, fabrication of cost-effective energy storage gadgets having significantly low self-discharge and gravimetric power density (GPD), aka specific power (measured in KW kg −1 ), coupled with significant gravimetric energy density (GED) aka specific energy (measured in Wh kg −1 ) is still a challenging task for the researchers. One possible solution in this direction is to design these storage devices with the salient features of a capacitor (a storage tool based on the principle of electrical double-layer capacitance [EDLC]) and a battery. Such devices in practical usage are termed as hybrid capacitors or SCs. These hybrid capacitors are expected to deliver enhanced GED without noticeable changes in the GPD, low self-discharge properties, and outstanding cycle life. Metal-ion-based supercapacitor (MISC; M denotes Li/Na) is a typical hybrid capacitor integrated with an entity having high GED that would act as anode and another entity having high GPD that acts as cathode, thereby offering wide potential window that proficiently enhances the GED. It has attracted significant interest owing to its possible applications in upcoming smart power grids, electric mobility, small electrical gadgets, and others. However, the practical implementation of MISCs is severely hampered due to the kinetic mismatch between the electrodes, which needs to be addressed. The present chapter discusses the feasible classifications, fundamental scientific principles, structure, and current innovations in the existing MISC's technologies, with a special emphasis on electrode materials and their performance characteristics. Finally, future emerging trends and possibilities of the MISCs as well as the associated challenges have also been reviewed.