# Application of the Supercapacitor for Energy Storage in China: Role and Strategy
## 3 Development of China's Supercapacitor Field  
### Market Trends, Upstream Materials, and Preparation Procession  
China's demand for supercapacitors is increasing year by year. Figure 4a shows the comparison of the scale growth of China and the global supercapacitor industry since the 13 th Five-year Plan period (2015-2019). In 2020, the China's supercapacitor market scale reached 14.38 billion Yuan, accounting for more than 70% of the global total, and China has become the largest supercapacitor market in the world, and the growth rate of supercapacitor market in China continues to be higher than the global ones. The upstream field of supercapacitor industry mainly consist of various raw materials, including electrode materials, electrolyte materials, diaphragm, etc. Electrodes and electrolytes are the key materials in the production of supercapacitors, which directly determine the main performance indexes of supercapacitors (such as the energy density, power density, cycle stability, etc.). Activated carbon is the low-cost electrode material with the highest utilization rate among EDLC electrodes. Activated carbon has an abundant pore structure, including micropores (less than 2 nm), mesopores (2\(\sim\)50 nm) and pores larger than 50 nm. It also has the characteristics of a large specific surface area. Although its conductivity is not very outstanding relative to metal oxides (1250-2500 S/m), it is still suitable for supercapacitors [20]. Carbon nanotubes have also been widely used in the research of supercapacitor electrodes due to their certain internal network, chemical and thermal strength, and electrical conductivity. Thermal graphene, another ideal electrode material for supercapacitor, has excellent mechanical strength and electrical conductivity, large specific surface area, high carrier mobility, and high chemical stability. In addition, transition metal oxides are redox-active materials that are also widely used in electrode materials. They are usually hybrid supercapacitors that exist in oxide and hydroxide structures. There are many kinds of transition metals, mainly used in the structure of transition metal oxides and various metal hydroxides, namely, nickel, iron, cobalt, titanium, molybdenum, vanadium, and niobium. Transition metal oxide (TMO) is a widely used electrode material. Using this material as the supercapacitor electrode material, the transition metal oxide supercapacitor has higher energy density and power density than that using carbon electrode material. Due to their reversible redox reactions, transition metal oxides (TMO) and conductive polymers (CPs) are widely used in Faraday capacitors. Conductive polymers have high conductivity, photoconductivity, nonlinear optical properties, and magnetic properties. It has the advantages of good flexibility, low production cost, high energy efficiency, large specific surface area, three-dimensional (3D) porous microstructure, and high capacitance energy density and so on. Conductive polymers are coupled with active substances and can be reversibly oxidized or reduced within a certain range. So, conductive polymers are widely used in supercapacitors [21; 22; 23; 24; 25]. Supercapacitors can be divided into button-type, winding-type, and large-type according to their manufacturing process and shape  
Figure 3: Different characteristics among three types of supercapacitors. structure. The supercapacitors of the three types can be roughly classified as below, 5F, 5-220F and above 200F. Figure 4b shows the market share and growth rate of three major types of supercapacitor in China from 2016 to 2020. In 2020, the market size of China's button-type, winding-type, and large supercapacitors was 3.247 billion yuan, 6.937 billion yuan, and 4.196 billion yuan respectively, with a year-on-year growth of 9.58%, 8.15% and 8.62 respectively. Figure 4c presents the manufacturing process flow chart of soft package supercapacitor.