Design and Preparation of Electrode Materials for Supercapacitors with High Specific Capacitance

Supercapacitors (SCs) have been explored as one of the electrical sources because of their fast charge and discharge rates, good safety, and long cycle life. However, the limited energy densities of SCs hinder their further application. Thus, current research on SCs focuses on increasing their energy density. Enhancing specific capacitance is an effective way to increase energy density. In this review, we describe several approaches to achieve superior electrochemical properties by optimizing electrode materials and electrolytes. Considering electrode materials, their electrochemical performance is related to their specific surface area, pore structure, and electroconductivity. On one hand, the optimization of specific surface area and pore structure can increase their content of exposed active sites as well as electrolyte ion conductivity, which is beneficial for improved specific capacitance. On the other hand, enhanced electroconductivity leads to higher specific capacitance. The specific capacitances of electric double-layer capacitors and pseudocapacitors have been increased by optimizing carbon-based materials and metal hydroxides/oxides, respectively. Moreover, specific capacitance can be further enhanced by adding a redox mediator to the electrolyte as a pseudocapacitive source. This review offers perspectives to aid the development of next-generation supercapacitors with high specific capacitance.