Development of Carbon Fiber-Based Electrodes for Lithium-Ion Battery

Abstract

Introduction To meet the increasing requirement on high energy density, power density and long cycle life of large-scale lithium ion batteries (LIBs), advanced electrodes which can afford more active material loading while reducing extra use of additives are desired. In light of this purpose, carbon fibers (CFs) are regarded as a potential material because they can be used as current collectors where more active materials can be loaded on their 3-dimensional (3D) electrically conductive network. In addition, CF-based current collectors enable a binder-free electrode design for lithium ion batteries and sodium ion batteries (SIBs). [1,2] In this work, we develop several CF-based electrodes for use in not only positive electrode but negative electrode of LIBs, demonstrating their characteristics in terms of electrode fabrication methods and electrode performances. Experimental For the fabrication of CF-based electrodes, two approaches, namely hydrothermal and sol-gel reaction routes, are applied. In the hydrothermal process, an electrodeposition of precursor was first carried out, followed by the hydrothermal reaction and post-calcination treatment to synthesize the target active material. For the sol-gel route, active materials were primarily synthesized in the sol-gel reaction step. After a calcination treatment of the gel, powder-type active materials can be obtained. Then, a slurry was prepared by mixing the powders with solvents and specific additives. After coating the slurry on CFs and drying, fabrication the CF-based electrodes were completed. SEM and XRD are generally used for the material analysis. With respect to the electrochemical evaluation, a coin cell (CR2032) was used to accommodate the CF-based working electrode and lithium metal foil as a counter/reference electrode. Results and Discussion According to the electrode performances, it is convinced that both hydrothermal and sol-gel routes are appropriate for the fabrication of CF-based electrodes. The physical properties, including morphology, chemical composition and crystallinity, vary depending on the fabrication methods and conditions. While the hydrothermal route is capable of binder-free electrode design, the sol-gel route offer the benefit to the formation of active materials with purer crystal phase and better crystallinity. Moreover, CF-based electrodes exhibit satisfactory electrode performances due to their 3D conductive structure, facilitating ion transport and electron conduction during the cell operation.