Fluorination of Cup-stacked Carbon Nanotubes, Structures and Properties
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Fluorination of Cup-stacked Carbon Nanotubes, Structures and Properties Hidekazu Touhara, Akiko Yonemoto, Kazunao Yamamoto, Shingo Komiyama, Shinji Kawasaki1, Fujio Okino, Takashi Yanagisawa2, Morinobu Endo2 Faculty of Textile Science and Technology, Shinshu University, Ueda 386-8567, Japan 1 Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan 2 Faculty of Engineering, Shinshu University, Nagano 380-8553, Japan ABSTRACT Cup-stacked carbon nanotubes (Cup-CNTs) was fluorinated in a temperature range RT-500℃ by 0.5-1 atm elemental fluorine. The F/C atomic ratio (CF0.4-CF1.2) and the color are strongly dependent on the fluorination conditions. The color of fluorinated Cup-CNTs (F-Cup-CNTs) varies from black, through gray and yellow to white. The form and morphology of the pristine tubes were well preserved after fluorination, and the fluorination results in the functionalization and modification of pristine Cup-CNTs with respect to electrochemical properties. The F-Cup-CNTs as cathodes for primary Li cells discharge satisfactorily with 100% cathode utility. INTRODUCTION Fluorination is one of the most effective chemical methods to modify and control the structural and physical properties of carbon materials [1, 2]. Fluorination of carbon nanotubes (CNTs) is also effective for their property control and functionalization of single-walled carbon nanotube (SWNT) sidewalls [3]. Recently，carbon nanotubes with cup-stacked morphology were developed as a novel type of tubular nano-sized carbon material[4, 5]. An interesting structural feature of the tubes is their tubular morphology consisting of truncated conical graphene layers which are stacked up in the tube direction. The edges of stacked cups are exposed to both outer surfaces and inner channel of the tubes. These structural features are of great interest in fluorination chemistry for nano-carbons. In this paper, we report the fluorination reaction of Cup-CNTs and structural properties of resulting compounds. We also show the performance of primary lithium cells with F-Cup-CNTs cathodes.
EXPERIMANTAL DETAILS Cup-stacked carbon nanotubes samples used in the present study were supplied by GSI Creos Corp. The method by which these tubes were prepared is a floating reactant method using iron pentacarbonyl as a catalyst precursor, and natural gas as a carbon feedstock in a continuous
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process [4, 5]. The tube diameters are in a range 50-150 nm, wall thickness of 10-30 nm, and lengths of up to 200μm. Fluorination was carried out by direct reaction of Cup-CNTs with elemental fluorine gas as follows. Prior to fluorination, Cup-CNTs samples were heated at 200℃ under vacuum for several hours in order to eliminate adsorbed water. The dried samples were fluorinated with 1 atm F2 at a temperature range RT-500℃ for 24 h, RT for 3 weeks, and 0.5 atm at RT for 3 weeks. Fluorinated Cup-CNTs were characterized by X-ray photoelectron spectroscopic (XPS) measurements by the use of an Ulvac-phi model 5600 with monochromatized Mg Kα X-ra
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