18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS 1 General Introduction Carbonaceous anodic materials have been used for lithium-ion batteries due to their good initial Coulombic efficiency and cycle performance [1-3]. However, much capacity is strongly demanded for applications to the larger energy consuming devices such as electric vehicles. Among many candidate materials, silicon-base materials have attracted huge interest because of the higher capacity (4200 mAh g - 1 , with the formation of Li 22 Si 5 ) than graphite (372 mAh g -1 ). Nevertheless, silicon anodes suffer from by two major disadvantages: the low electric conductivity and huge volume change during lithium-ion insertion and extraction processes of the lithium-ion battery, leading to pulverizations in the structure. The pulverizations lead to the drastic change of the anode structural morphologies and poor contacts between the Si particles and current collector. Many efforts have been made to overcome these problems by reducing the particle size [4, 5], using silicon-based thin films and nanowires [6, 7], and using composite materials [8-10]. Among them, one of the most promising strategies is to composite nano-sized silicon with a carbon matrix, in which the carbonaceous material acts as both a structural buffer and an electric conductive material. In carbonaceous materials, carbon nanofiber (CNF) was proposed as anode material [11-13]. Compositing Si nanoparticles with CNF is an effective methods to prevent severe pulverization of Si; hindering Si particle aggregation, providing long distance electron conductivity and eliminating the need for conducting additive [14, 15]. However, the discharge capacity of CNF is not so high and the cycling performance is not good because of the high surface area of CNF itself (100~200 m 2 g -1 ). Our research group has proposed a novel solution to moderate volume expansion of anode by growth of CNF on the surface of silicon particles to reduce the volume expansion by rapping as to provide space among them for absorbing the volume expansion [11]. Jang et al. has demonstrated that the Si-CNF composites showed better performance but still observed capacity decreasing (23%) after 20 cycles because of low electrical contact area between CNFs grown on the surface of Si particles (presumably point contact). In this work, the Si-CNF composites were hybridized with commercial graphite to afford larger contact area between the composites (CNFs on the composites) and graphite (hopefully line contact), for improving of the cycling performance through stable contact characteristic and good electric conductivity of CNF and graphite. 2 Experimental 2.1 Sample Preparation Nano-sized silicon particles (20 nm and 50 nm, Nanostructured & Amorphous Materials, Inc., USA) were used as starting materials. Helium, methane, carbon monoxide and hydrogen gases were applied for pyrolytic carbon (PyC) coating and CNF growth. PyC coating was carried out in a horizontal furnace using a quartz boat and heated to 900 o C at a heating rate of 10 o C min -1 under flowing He gas. When the temperature reached to 900 o C, the gas flow was changed mixed gas of CH 4 and H 2 (4: 1) and maintained for 1 h to coat the PyC on the surface of Si. The reactor was cooled down to room temperature under flowing He gas. The amount of coated PyC was 20.9 wt % for 20 nm Si and 15.6 wt% for 50 nm Si on the weight basis. The obtained PyC-coated Si particles were designated as Si/PyC. Reagent grade iron nitrate enneanhydrate [Fe (NO 3 ) 3 ·9H 2 O] (Wako Pure Chemical Industries, Ltd, Japan) as the CNF growth catalyst and Si particles were dissolved into ethanol, and then the solution HYBRIDIZED SI-CNF NANOCOMPOSITE AND GRAPHITE AS A HIGH PERFORMANCE ANODE FOR LI-ION BATTERY T.H. Park 1 , J.S. Yeo 1 , J. Miyawaki 2 , I. Mochida 3 , S.H. Yoon 1, 2 * 1 Interdisciplinary Graduate School of Engineering Sciences, Kyushu University 2 Institute for Materials Chemistry and Engineering, Kyushu University 3 Research and Education Center of Carbon Resources, Kyushu University *Corresponding author (yoon@cm.kyushu-u.ac.jp)