Functionalization of Carbon Materials as Energy Conversion Materials by Surface Modification

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1. Surface fluorination, fluorination process and electrochemical behavior of petroleum cokesPetroleum cokes (original, heat-treated at 1860℃, 2300℃ and 2800℃) were fluorinated at 150℃, 200℃ and 300℃ by 0.3 bar F_2 for 2 min. Original petroleum coke was somewhat fluorinated, however, the fluorination of other heat-treated cokes were less. BET surface areas of petroleum cokes heat-treated at 1860℃ and 2300℃ were slightly decreased by fluorination while that heat-treated at 2800℃ was increased. Meso-pores with diameters of 5-15 nm were simultaneously increased for all the cokes. Fluorination process of graphite was monitored by X-ray diffraction and Raman spectroscopy for samples fluorinated at room temperature, 380℃ and 515℃. Fluorine-intercalated phase with sp^2 planar graphene layers is formed at first, and then converted to graphite fluoride with puckered graphene layers. The capacities of surface-fluorinated petroleum cokes and first coulombic efficiencies were increased by 10% and 5-10%, respectively.2. Functionalization of carbon materials by chemical vapor infiltration (CVI)Pyrocarbon was infiltrated into carbonized filter paper at 950℃ by CVI method using propane and hydrogen. Infiltrated pyrocarbon has higher crystallinity and smaller surface area than carbonized filter paper. Coulombic efficiency of the pyrocarbon was increased by 10-15% probably due to decrease in the solvent decomposition.3. Improvement of characteristics of graphite electrode by fluoride additivesFluorine-containing esters and ethers were examined in 1M LiClO_4-ethylene carbonate/diethyl carbonate solution. Addition of a small amount of fluorine compound improved the charge/discharge characteristics of graphite electrode at 0℃〜-10℃. This may be because fluorine groups incorporated in the surface film on graphite facilitates the diffusion of Li^+ ion.