Research Progress of MnO₂ as Supercapacitor Electrode Materials

The supercapacitor occupies an irreplaceable position in the field of energy storage devices due to its ultra fast charge/discharge speed. In addition, it also has many other advantages, such as long cycle life, easy maintenance, high safety and environmental protection, and low cost. The specific capacitance of supercapacitors represented by carbon based materials is usually low, which is difficult to meet the demand for high energy. Pseudocapacitors represented by various metal compounds are favored by modern society for they can store more energy through rapid Faraday reaction. Among which, MnO₂ is one of the traditional pseudocapacitor electrode materials first proposed.It has rich crystal phase structures, and some of the structures can act as tunnels for the hydrolysate ions' fast insertion/extraction. It has high theoretical specific capacity, but it has some problems, such as low electronic conductivity and poor cycle stability. Here are introduced the energy storage mechanism and research status of two representative types of MnO₂ with α phase and δ phase, introduced the commonly used solutions to their existing problems, and put the prospect of the large-scale application of MnO₂.