Electrochemical Capacitors (ECs) are a class of energy storage device that fill the gap between high energy density batteries and high-power-density electrostatic capacitors. ECs show shorter charge/discharge time and higher power density compared to batteries. However, to use ECs as alternatives to batteries, a significant increase in energy density is required. Although critical to the U.S.'s energy future, development of ECs has been hindered by the lack of cost-effective electrode materials that can store more energy. As a cheaper alternative transition metal, manganese (Mn) is abundant and environmentally-friendly. Manganese oxide shows theoretical capacitance of ~800 F g-1, which is comparable to that of RuO2. However, owing to low electronic and ionic conductance, manganese oxide powder exhibits much lower specific capacitances. This book discusses studies of charge-storage mechanism of manganese oxide nanomaterials for ECs. It also discusses sustainable electrode materials made from electrospun alkali lignin-based carbon nanofibres for high performacen supercapacitors; new strategies for the improvement of SC energy density by covalent and non-covalent addition of qunones of carbon surfaces; maganese dioxide based SCs; supercapacitors test methods; and hydrogenated barium titanate films and their potential for integrated SCs.