Chapter 17 - Metal-based hybrid capacitors

Abstract

A hybrid supercapacitors performance is based on the combination of energy (Battery-level) and power densities (Supercapacitor-level) with cycle life in a single device. It is made up of an anode and a cathode that belongs to battery and supercapacitor material for enhancing the energy and power densities. In general, the battery-type electrodes store ion/electrons simultaneously through intercalation, phase change, or conversion reactions with generally sluggish kinetics due to solid-state transport. Whereas, in the supercapacitor, electrodes store the ions/electrons by electrostatic adsorption with fast kinetics. However, the limited number of ions that can be accommodated on the electrolyte-electrode interface is a bottleneck for capacity improvement. It remains a substantial challenge to achieve high capacity and rapid kinetics of ion/electron storage synchronously in one electrode. This can be overcome by decoupling of electrons and ions storage in a single electrode with an aid of nanostructured metal-based materials. The major advantages of nanostructured based metals are, to create more active sites, high surface area, more efficient diffusion pathways for both electron transfer and ion diffusion, less structural integrity, reduce volume expansion during charging/discharging, low capacity fading for long cycles, and induces oxygen vacancies which lead to an increase in the electrical conductivity. Due to these superior properties, the utilization efficiency of the active materials is increased with enhanced specific capacitance and cyclic stability. Hence, this chapter mainly focused on the effect of metal-based nanostructures in HSCs which covers the visible feature of components, energy storage, and conversion mechanism, selection and optimization of electrode materials and electrolytes as well as electrochemical performance evaluation and potential application.