SUMMARY

Electrochemical energy storage systems, including rechargeable batteries and electrochemical capacitors (ECs), have several advantages for effective renewable energy storage, such as long cycle life, high efficiency and pollution-free operation. Nowadays, owing to the environmental and resource issues, the development of low-cost, sustainable, and high-performance electrode materials for electrochemical energy storage devices are highly desirable. Carbon materials are abundant in nature in various forms and also renewable. Thus, considerable efforts have been devoted to developing high performance carbon-based electrodes. However, in carbon-based cathodes, energy can be stored through the electrical double layer process, which resulted in low capacities in a range of 40~70 mAh/g. In order to enhance the performance of the carbon-based cathodes, additional energy storage process should be introduced into carbon-based electrodes, besides the electrical double layer process. Incorporating rapid and reversible surface redox-reactions has been a promising strategy for enhancing the energy density of supercapacitors. Thus, in my research, redox-active oxygen was firstly introduced onto various nanocarbon materials, such as graphene, carbon nanotubes, and these functionalized carbon-based cathodes exhibited enhanced capacity up to 160 mAh/g, which is 2-3 times higher than that of commercial activated carbon. Secondly, functional carbonaceous materials were synthesized by a simple hydrothermal carbonization process of earth abundant biomass, such as glucose. By controlling the morphology of the carbonaceous materials, the capacity can be further enhanced to ~250 mAh/g. Lastly, the development of high performance, sustainable organic electrode materials was proposed based on carbonyl-based compounds which can be easily found or prepared from natural products.