A comprehensive review on supercapacitors: Their promise to flexibility, high temperature, materials, design, and challenges

Energy storage materials have been receiving attention during the past two decades. Supercapacitors, in specific, have emerged as promising energy storage devices, especially for flexible electronics. The development of supercapacitor materials is crucial to advance their performance and multifunctionality. Supercapacitors have been shown to possess higher energy densities than conventional capacitors and higher power densities than batteries. Advancements in electrochemical supercapacitor cells are heavily sought after. This review showed that the progress made in supercapacitors’ materials led to the development of novel electrode materials, heat-resistant separators, flexible supercapacitors, and highly conductive electrolytic solutions. Therefore, supercapacitors' electrochemical performance, power density, charge storage density, specific capacitance, and charge/discharge rates were eventually enhanced. Moreover, research is being conducted to operate supercapacitors in soft electronics by improving their solid-state flexibility. This paper also provided a comprehensive overview of the recent developments in high-temperature capacitive energy storage, the various applications of supercapacitor cells in the industry, supercapacitors design, as well as the challenges involved. This work concluded that the biggest challenge of producing supercapacitors is manufacturing them at a low cost to make them economically viable energy storage options.