Synthesis of metal oxide/graphene hybrid nanocomposites and its application for energy storage devices

Abstract

Supercapacitor is charge storage devices which have different from the Ni-MH, Li-ion battery, etc. Supercapacitor is composed of an electroactive material on current collector, an electrolyte, and a separator. For charge storage mechanism, two-types of supercapacitors were developed; First is electrochemical double layer capacitors (EDLCs), which are operated by ion adsorption/desorption on surface of electroactive materials. Carbon-related materials such as activated carbon, carbon nanotube, carbon nanofiber, and graphene have been used for EDLCs electrode materials. EDLCs have several advantages such as low resistance and long cycle stability. Second are pseudocapacitors, which are worked by redox reaction of metal oxide material. Among the pseudocapacitors, RuO2 has been extensively studied in electrochemical capacitor electrodes because of its high specific capacitance. However, RuO2 has the drawbacks of high cost and toxicity. Therefore, many studies have recently been directed toward replacing RuO2 with inexpensive transition-metal oxides such as Manganese-based, Nickel-based, Cobalt-based, Vanadium-based, Titanium-based, and Zinc-based oxide materials. Pseudocapacitors have high energy density compared to EDLCs, but it has high resistance of electroactive materials, resulting low cycle stability. In chapter 2, metal oxide was prepared, and studied the effect of intercalated anion and surface area on capacitance. In chapter 3, nitrogen-doped graphene was studied as EDLCs types of supercapacitors. In chapter 4, metal oxide/graphene nanocomposites were prepared by novel method and investigated by several factors for high energy density and long cycle stability. Detailed information for each chapter is described as below. In chapter 2-1, hierarchical microspheres composed of wrinkled α-Ni(OH)2 nanosheets were synthesized from an aqueous solution containing nickel salts, hexamethylenetetramine, 1-butanol, and dodecyl sulfate. The exchange of intercalated ...