ROLL-TO-ROLL SYNTHESIS OF VERTICALLY-ALIGNED CARBON NANOTUBE ELECTRODES FOR ELECTRICAL DOUBLE LAYER CAPACITORS
Margarita Arcila-Velez, Jingyi Zhu, Anthony Childress, Mehmet Karakaya, Ramakrishna Podila, Apparao M. Rao, Mark E. Roberts.
Clemson University, Clemson, SC.
Electrochemical double layer capacitors (EDLCs) have emerged as promising solutions for high power/high energy applications. The unique properties of carbon nanotubes (CNTs) such as high electrical conductivity; electrochemical, mechanical, and chemical stability; high surface area; and low mass density, make them suitable candidates for EDLC electrodes. Vertically-aligned, multi-walled CNTs (VACNTs) have been considered for use in EDLCs due to their facile synthesis and the ability to control the ion-accessible surface. Chemical vapor deposition (CVD) has emerged as a practical and reliable method for VACNTs production, offering versatility in terms of controlling CNT characteristics and relatively low temperature requirements (<1,000 Â°C); however, technological advances are limited by the lack of continuous and scalable synthesis methods. Three primary factors limit continuous manufacturing of nanomaterials: substrate size determined by reactor geometry, requirements of complex catalytic substrate preparation, and high operating temperatures that are incompatible with traditional current collectors (e.g., Al foil). In this work, we present a scalable roll-to-roll process for synthesizing forests of VACNTs on inexpensive Al foil ribbons which are continuously drawn through a CVD reactor operating at ambient pressure and a relatively low growth temperature (600 Â°C). EDLC electrodes comprising VACNT forests synthesized in continuous and stationary CVD processes are directly assembled into supercapacitor cells, which yield high power densities (1,270 W/kg) and energy densities (11.5 Wh/kg). These devices exhibit very low internal series resistance due to their intimate contact with the current collector and excellent cycle stability with no loss in performance over multiple thousands of cycles.