Carbon Based Nanomaterials for Electrochemical Energy Storage Applications
Tour, James M.
Doctor of Philosophy
Ever-growing energy needs, limited energy resources, and the need to decrease soaring greenhouse gas emissions have brought about an urgent demand on the pursuit of energy alternatives, includ¬ing both renewable energy sources and sustainable storage technologies. Electrochemical capacitors (ECs) and reversible lithium ion batteries (LIBs) are two promising energy storage technologies that are well positioned to satisfy this need in a green energy future. However, their large-scale deployment has been significantly hindered by several major technological barriers, such as high cost, intrinsically poor safety characteristic, limited life, and low energy density and/or power density. One promising solution is to develop advanced electrodes materials for these devices. In this thesis, various nanomaterials and nanostructures have been developed to improve the electrochemical performance of ECs and LIBs. My thesis begins with the introduction of energy storage systems of ECs and LIBs in Chapter 1. Chapter 2 to 4 discuss the synthesis of nitrogen-doped carbonized cotton, brush-like structured nanocomposites of polyaniline nanorods-graphene nanoribbons, laser induced graphene-MnO2, and laser induced graphene-polyaniline and their applications in ECs. All of them demonstrated excellent performance in energy storage, showing high potential applications as electrode materials in ECs. Chapter 5 to 8 discuss a graphene wrapping strategy designed to synthesize graphene-metal oxide/sulfide-graphene nanoribbons, including graphene-MnO2-GNRs, graphene-NiO-rGONRs, graphene-Fe3O4-GNRs, and graphene-FeS-GNRs. This sandwich structure mitigated the pulverization of these anode materials from their conversion reactions during extended cycling, leading to a large improvement in the cycling stability of anodes in LIBs. To address the volume change of SnO2-based anode materials, a facile and cost-effective approach was developed to prepare a thin layer SnO2 on reduced graphene oxide nanoribbons. Chapter 9 discusses how this nanocomposite demonstrated excellent cycling stability with high capacity. For LIBs cathode materials, a hierarchical polyaniline matrix was designed to reduce the dissolution of the intermediate lithium polysulfide into the electrolyte as shown in Chapter 10. This material showed great improvement in cycling stability with high capacity.