This thesis aims to increase energy storage performance of supercapacitor devices by improving the energy density of supercapacitors without significantly compromising power density. Different strategies were used in this research, including using battery materials in place of electrodes, increasing the potential window of the supercapacitor, and employing soluble dual-redox additives. These strategies led to the discovery of several high power and high energy density energy-storage technology applications that have the promising potential to be commercialized.