Design and Synthesis of Multifunctional Carbon Materials for Energy Storage Devices and Beyond
Energy storage technologies are receiving a great deal of attention today due to their potentials to expedite current efforts to make a low carbon energy future possible. Electrochemical energy storage systems – supercapacitors and batteries – have demonstrated their ability to bring multiple benefits as a viable and complementary technology for making renewable energy resources more available to people. Lithium-ion batteries, as a mature electrochemical energy storage technology, currently dominate the portable electronics market, and are continuously trying to expand into new markets with the global trend towards electric vehicles and smart girds. However, their high cost associated with performance improvement prevents them from penetrating into these new applications. Therefore, advances in new materials that could be made available in large quantities at low cost, while satisfying various industry requirements and being safe and durable, are extremely important in order to overcome the above limitations. Improving the performance metrics of electrochemical energy storage devices through rational design of carbon materials has been the major focus of the research presented in this dissertation. A variety of carbon materials including activated carbon, carbon nanotubes, graphene, and carbon aerogel have been investigated. However, as no material is perfect, each having its own advantages and disadvantages, it is unlikely that a single material could provide a complete solution to problems of the existing electrochemical energy storage systems.
This dissertation proposes design strategies that lead to significant improvements in the performance of electrochemical energy storage devices by appropriate choice of carbon materials and further development of novel electrodes. Chapter 2 describes an approach of designing a two-dimensional carbon thin film electrode with a double-layered structure composed of polyetheretherketone-derived microporous carbon and graphene. Such layered combination of the two carbons shows synergistic properties by complementing each other, therefore creating a highly porous conductive carbon films for supercapacitors. Chapters 3 through 6 highlight a novel method for developing a special type of highly conductive and porous three-dimensional materials, which are polymer-cross-linked carbon aerogels, namely carbon x-aerogels. These carbon x-aerogels constitute the major contributions of this dissertation. Carbon x-aerogels are designed to solve problems with conventional carbon aerogels. They are not only porous and conductive, but also mechanically robust with high compressibility with fast recovery. This multi functionality makes them promising for developing high-energy-density supercapacitors (Chapter 3) and next-generation rechargeable batteries that will eventually power the beyond current lithium-ion technology, such as lithium-oxygen (Chapter 4) and lithium-sulfur batteries (Chapter 5). Chapter 6 describes another potential application of carbon x-aerogels beyond its utilizations in electrochemical energy storage devices, which is its application as novel electrode materials for capacitive deionization that can make the current water treatment technology more cost-effective. In conclusion, the most important achievement in this dissertation is the successful development of carbon x-aerogels, which currently is laying the groundwork for future research on materials design and which ultimately will provide practical solutions to challenges in energy storage technology and beyond.
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