Date of Graduation
Statler College of Engineering and Mineral Resources
Chemical and Biomedical Engineering
Increasing energy density of electrochemical capacitors (ECs) is crucial for their applications in energy storage devices requiring short peak power pulses as well as long-term operation. ECs are operated via two primary charge mechanisms, that is, the electrochemical double-layer capacitance and the pseudocapacitance. In the thesis, the carbon materials and LiMn2O 4, which generate double-layer capacitance and pseudocapacitance, respectively, have been investigated. The effects of specific surface area, pore structure and surface functionality on the energy storage performance of ECS have been studied.;Micro-porous (<2 nm) carbon with pores inaccessible to the solvated ions may limit the ion diffusion, resulting in a low rate capability. Hence this work attempts to generate hierarchical macropores/mesopores/micropores in the electrode material. Flexible, self-sustained and hierarchical porous carbon nanofibers (CNFs) are fabricated using terephthalic acid as the sacrificial agent. After sublimation and carbonization, the electrospun mat is converted to a hierarchical porous carbon framework. The high specific capacitance and good rate capability are associated with the unique hierarchical porous structure of the as-prepared CNFs. Both the outer fiber surface and inner porous structure can be accessible for charge accumulation through pores on the surface. Hierarchical macropores/mesopores in the fiber also help accelerate the ion-diffusion into inner micropores.;Besides fossil resources, renewable biomass has also been explored as the source material for supercapacitors in the present work. Lignin, the major aromatic constituent of plant and woods, is utilized as the carbon precursor to prepare the mesoporous lignin-char. The lignin-derived carbon is prepared by taking an advantage of the organic-organic self-assembly method, which allows the direct formation of mesoporous polymer composite from carbon precursor and block copolymer, and conversion to porous carbon by carbonization. Hierarchically porous carbon (HPC) with pores at different scales has been obtained after alkali activation. The experimental results show that the appropriate pore size distribution can ensure high power density and high energy density due to the short diffusion distance and the minimized electric resistance. Utilization of biomass as the source materials for supercapacitors will reduce the costs for fabrication of energy storage devices.;Developing asymmetric supercapacitors is an alternative effective way to obtain high energy density for an enlarged potential window and additional pseudocapacitance. LiMn2O4 nanoparticles have been fabricated with a facile and cost-effective method using carbon black as the template. The spinel structured LiMn2O4 exhibits a high specific capacitance in a three-electrode system. An asymmetric supercapacitor has been made with the as-prepared LiMn2O4 nanoparticle as the cathode and the commercial activated carbon as the anode in a Li 2SO4 aqueous solution. The asymmetric supercapacitor shows a good energy capacity and excellent cycling stability.
Hao, Shimeng, "Hierarchically Porous Carbon Materials and LiMn2O 4 Electrodes for Electrochemical Supercapacitors" (2015). Graduate Theses, Dissertations, and Problem Reports. 5760.