Energy densities of supercapacitors are not very high. At present, there is still a certain gap between supercapacitors (<20 Wh kg −1) and batteries (30–200 Wh kg −1) in terms of energy densities, how to improve the energy density is still the research focus and difficulty in the field of supercapacitors. 5,33,34 Improvement of manufacturing process and technology is an effective way to improve the storage capacity of supercapacitors, but in the long run, it is essential and difficult to find new electrolyte and electrode active materials with higher corresponding electrochemical performance.