The Design And Preparation Of High-Performance Silicon/Carbon Composite Anode For Lithium-Ion Batteries

The increasing demand for high-performance energy storage devices has driven extensive research into developing advanced lithium-ion batteries (LIBs) for various applications, including electric vehicles, portable electronics, and grid energy storage. Anode materials play a critical role in determining the overall performance of LIBs. In this dissertation, the investigation of silicon-based anode materials synthesis, characterization, and electrochemical performance was conducted for high-performance lithium-ion battery (LIB) applications. Four projects (Chapter 3 through 6) will be included in this dissertation. Chapter one includes the background and motivation of developing high-performance anode material for LIBs, followed by the hypothesis, scope of work, and significance of this dissertation. Chapter 2 includes the approach used in this dissertation. Chapter 3 focuses on addressing the challenges of silicon-based anodes for LIBs by synthesizing a porous 3D humic acid-derived graphene and micron-sized silicon composite anode (Si@G foam). Raman spectra confirm the in-situ formation of graphene and Scanning Electron Microscopy (SEM) images show the 3D structure with silicon particles evenly distributed. The Si@G composite-anode exhibits excellent reversible capacity, high-rate capability, and outstanding cycling stability. It displayed a reversible capacity of approximately 656 mAh/g at a current density of 50 mA/g, and a high-rate capability of approximately 433 mAh/g at a current density of 800 mA/g with cycling stability approximately 90% capacity retention after 300 cycles. The graphene foam structure serves as an electrical conductor for the active materials and volume expansion support for silicon particles during the charge/discharge cycle for LIBs, offering potential for advanced silicon-based anodes in high-performance LIBs. Chapter 4 explores the optimization of SiOx/graphite anode design for industrial LIBs applications using the Taguchi method. This method evaluates the effects of conductive agent-to-binder ratio, conductive agents’ combination, and binders’ combination. The optimal factors resulted in a significant improvement in the anode\u27s electrochemical performance, with an Initial coulombic efficiency (ICE) of 88% and an initial de-lithiation capacity of 439 mAh/g. After 400 cycles, the anode achieved 90% rotation. The Taguchi design method is validated by electrochemical kinetic analysis, demonstrating its usefulness in optimizing SiOx/graphite anodes for LIBs. The application of graphene coatings enhances the usability of SiO anodes by improving electronic conductivity and mitigating volume expansion. Chapter 5 investigates the use of non-woven carbon fiber substrates as current collectors for electrodes in high-energy density LIBs. Non-woven carbon fiber substrates offer structural stability, mechanical strength, and high electrical conductivity, which enables efficient electron transfer and better withstands volume changes during cycling. The study shows that non-woven carbon fiber substrates outperform traditional copper/aluminum current collectors in energy density. The energy density of the anode was increased by 70%, and the energy density of the cathode increased by 23%. The study found that anodes and cathodes using non-woven carbon fiber substrates exhibited higher specific capacity densities compared to those using traditional copper/aluminum current collectors. While the ICE needs improvement, non-woven carbon fiber substrates show exciting potential for enhancing LIB electrochemical performance. Chapter 6 explores the use of chemical pre-lithiation to improve the electrochemical performance of the SiOx/graphite composite anodes for LIBs, especially for the ICE. The ICE increased from 88% to 98% using an aryl lithium reagent impregnation method, and the anode\u27s energy density, rate capability, and cycling performance were significantly enhanced. Pre-lithiation methods are promising for improving LIB performance by increasing initial reversible capacity, initiating volume pre-expansion, and creating a synthetic solid electrolyte interface (SEI). SEM imaging with osmium tetroxide staining showed a stable SEI layer after pre-lithiation and cycling tests. Based on the results, the pre-lithiation process for the anode could be used in the industrial process for LIBs anode production. In summary, this dissertation focuses on the silicon-based composite anode materials’ synthesis, characterization, and electrochemical performance evaluation, as well as the implementation of a pre-lithiation technique, provides valuable insights for the development of high-performance anodes for LIBs. The promising results obtained from the SiOx and graphite composite anodes, combined with the benefits of pre-lithiation, display the potential of these materials for enhancing the overall performance of LIBs. The findings of this research will serve as a valuable resource for the research field, battery manufacturers, and engineering work on the development of next-generation LIBs