Enhancement of Volumetric Capacitance of Binder-Free Single-Walled Carbon Nanotube Film via Fluorination

Robust electrode materials without the addition of binders allow increasing efficiency of electrical storage devices. We demonstrate the fabrication of binder-free electrodes from modified single-walled carbon nanotubes (SWCNTs) for electrochemical double-layer capacitors (EDLCs). Modification of SWCNTs included a sonication in 1,2-dichlorobenzene and/or fluorination with gaseous BrF3 at room temperature. The sonication caused the shortening of SWCNTs and the splitting of their bundles. As a result, the film prepared from such SWCNTs had a higher density and attached a larger amount of fluorine as compared to the film from non-sonicated SWCNTs. In EDLCs with 1M H2SO4 electrolyte, the fluorinated films were gradually defluorinated, which lead to an increase of the specific capacitance by 2.5-4 times in comparison with the initial values. Although the highest gravimetric capacitance (29 F g-1 at 100 mV s-1) was observed for the binder-free film from non-modified SWCNT, the fluorinated film from the sonicated SWCNTs had an enhanced volumetric capacitance (44 F cm-3 at 100 mV s-1). Initial SWCNT films and defluorinated films showed stable work in EDLCs during several thousand cycles.