Capacitor to Supercapacitor

Supercapacitors bridge the gap between conventional electrolytic capacitors and batteries. These are capacitors with electrochemical charge storage. The basic equations used to describe the capacitors are same in the case of supercapacitors but their mechanism of energy storage is different. Various electrode-active materials such as activated carbon, mesoporous carbon, carbon nanotubes, graphene, etc., are invariably used in the supercapacitors with high performance. Both aqueous and organic electrolytes are used in supercapacitors but high voltage can only be delivered by the supercapacitors manufactured with organic electrolytes. However, the cycle life of aqueous electrolyte-based supercapacitors is high when compared with the organic ones. The present and future flexible and wearable technologies necessitate the development of flexible solid-state capacitors to supply them power. Supercapacitors are found applications in a variety of fields such as electronics industry, hybrid electric vehicles, and power supplies. The two major demerits of the present supercapacitors are low energy density and high cost. Hence, novel low-cost supercapacitors should be developed with high energy density to fulfill the needs of society. The present chapter discusses the Faradaic and non-Faradaic processes, types of supercapacitors, structure—i.e., electrode, electrolyte, electrolyte membrane, and current collector—key parameters for estimation of performance, electrochemical characterizations, etc.