**3. Supercapacitors offer many advantages compared with other energy storage devices**

Traditionally, batteries are the main energy storage centers in devices, with a hard shell and the toxicity of the electrolyte in coin cells. Compared with lithium-ion batteries, the cell configurations of supercapacitors will be much simpler and safer due to the use of water or polymer gel electrolytes instead of flammable and moisture-sensitive organic electrolytes. Furthermore, the fast and highly reversible double-layer capacitive and/or pseudocapacitive energy storage mechanism of supercapacitors will enable a significantly better high-power capability and cycling stability compared with lithiumion batteries. Even if the lower energy density of supercapacitors restricts the wide application of supercapacitors, due to their superior high-power performance, long-term cycling stability, and high safety, supercapacitors have been regarded as promising candidates for energy storage in some applications, as introduced in the following section.
