In a broad sense, energy storage includes the storage of basic fuels (coal, oil, natural gas, etc.), secondary fuels (gas, hydrogen, solar fuels, etc.), electrical energy storage, and heat storage. In a narrow sense, energy storage refers to a series of measures to store the energy produced by chemical or physical methods [24]. The scope of this book is electrical storage, i.e., electrical energy storage, which mainly includes pumped storage, compressed air energy storage, various electrochemical energy storage, flywheel energy storage, supercapacitors, etc.