ABSTRACT
The global demand for energy is continuously increasing. At the same time, the NOx and COx derived from combustion of nonrenewable mineral energy sources is leading to serious environmental pollution and global warming. It is urgent to limit the levels of pollution and reduce the emission of carbon dioxide and nitrogen oxides. Consequently, to exploit renewable energy sources, including wind power, geothermal resource, tide power, and solar power, is very important. However, these renewable energy sources present new challenges due to the dependence on the weather or climate, and time or season. As a result, energy from these renewable sources must be stored when the power is excessive and released when the power is not enough to meet the demand. Therefore, energy
storage technologies are an integral and indispensable part of our future life. There are several kinds of energy storage technologies such as ϐlywheel, chemical power sources, and compressed air (Wang et al., 2008). Considering of the comprehensive attributes of each storage technology such as cycling life, self-discharge, expense and investment cost, chemical power sources, including batteries and supercapacitors (Wu et al., 2008), are of great commercial interest. Ragone plots (energy density vs. power density) of different batteries and supercapacitors are shown in Fig. 13.1a (Service, 2006). Compared with batteries, supercapacitors accumulate electrical charge only at the electrode surface, rather than within the entire electrode, so they have relative lower energy densities. The charge-discharge process is not conϐined by ionic conduction into the electrode bulk, thus supercapacitors can operate at high rates and provide high power density (Koetz and Carlen, 2000). In addition, most materials of the supercapacitors do not participate in redox reactions, so there is little deterioration in the electrode, which has good cycling characteristics, and maintenance can be unnecessary.
