Binder-Free Composite Electrodes for Energy Storage Devices Using Networks of Carbon Nanotubes as a Multifunctional Matrix

• Other Authors: Smithyman, Jesse (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Materials science; Materials
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-4633

The improvement of electrical energy storage (EES) devices such as batteries and electrochemical capacitors (ECs) is crucial to the widespread adoption of electric drive vehicles and the increased mobility of portable electronics. This research takes a unique approach to the improvement of EES devices through the investigation of a novel nanocomposite system to improve the performance of particle based electrodes. The majority of commercially available batteries and ECs have electrodes fabricated from a powder of fine particles (typically with particle sizes on the order of several µms). There is a severe lack of options for transforming these powders into usable electrodes. The traditional electrode fabrication method is to mix the active material powder with a polymer binder to form a sheet or film, which can then be implemented into the device. However, reliance on and incorporation of the polymer binder introduces several disadvantages and performance limitations. In this research, porous networks of carbon nanotubes (CNTs) are investigated to replace the polymer binder in the fabrication of particle based electrodes for electrochemical devices. The multifunctional CNT networks provide the supporting structure and electron conduction pathways to create freestanding and flexible composite electrodes with high electrical conductivities (50 - 100+ S/cm). Two case studies were carried out to explore the properties and performance of the new electrode structure: 1) Activated carbon (aC) particle based electrodes for electrochemical capacitors and 2) Silicon (Si) particle based electrodes for lithium-ion batteries. Samples were fabricated and characterized with an emphasis on obtaining processing-structure-property relationships to guide further development of these unique nanocomposite materials. The aC-CNT electrodes showed specific capacitances of ~50 F/g (in 6M KOH) with less than 10% capacitance loss after 30,000 cycles; demonstrating the ability of the CNT networks to maintain structural integrity during operational conditions. Si-CNT electrodes had high coulombic efficiencies (> 90%) and initial reversible capacities of over 2000 mAh/g. Additionally, fundamental issues are addressed such as possible electrode failure mechanisms and the limits of particle weight fractions that are achievable. Knowledge of the maximum weight fraction of particles obtainable within the CNT networks is important to determine the feasibility of the electrodes for commercial use. A volume-fraction-limited phenomenon is proposed for the mechanism of the particle loading limit and discussed with supporting evidence. === A Thesis submitted to the The Graduate School in partial fulfillment of the requirements for the degree of Master of Science. === Fall Semester, 2010. === November 12, 2010. === carbon nanotube, binder-free, nanocomposite, electrode, battery === Includes bibliographical references. === Zhiyong Liang, Professor Directing Thesis; Tao Liu, Committee Member; Hsu-Pin Wang, Committee Member; Jianping Zheng, Committee Member.