| This thesis describes a novel method to prepare boron-containing carbon based materials from boron-containing precursors. The chemistry involve the synthesis of 9-chloroborafluorene and other heterocyclic boron-containing aromatic hydrocarbons and the transformation of these precursors to carbon based materials. Specifically, 9-chloroborafluorene was first converted to a polymeric precursor and then distilled to produce a boron-containing meosphase.; This liquid crystalline B-pitch was then pyrolyzed at various temperatures to produce B/C materials, in high yields, with the desired crystalline microstructures and morphologies. During pyrolysis, boron is substitutionally incorporated in the graphitic structure and it also catalyzes the graphitization reaction. Large crystallite sizes and small interlayer spacings were observed by x-ray diffraction measurements.; The co-carbonization of our precursor and conventional carbon precursors was evaluated. Co-carbonization of the 9-chloroborafluorene with a commercially available pitch resulted in a highly anisotropic carbon. Furthermore, this method is unique in that both components of the mixture provided carbon residues upon pyrolysis. By adding a small amount of 9-chloroborafluorene, the yield of low temperature carbon was dramatically improved from that obtainable from commercial pitches. This effective method resulted in the preparation of a broad range of B/C materials with different boron contents. Co-carbonization provided direct evidence for boron enhanced graphitization. The graphitization temperature of pitch can be lowered by several hundred degrees by incorporating a small amount of B/C precursor. Large crystal sizes with low interlayer spacing, similar to that of synthetic graphite, were obtained at 2300{dollar}spcirc{dollar}C.; In addition, other applications of the our B/C material were investigated. It was found that the oxidation resistance of the boron-containing carbon-based materials was much higher than that of synthetic SP-1 graphite. The oxidation results indicated that the mechanism of protection was based on specific site blockage by boron oxide. Finally, preliminary investigation of the electrochemical performance of the B/C material demonstrated its potential application in lithium secondary batteries. Electrode made from our B/C material was shown to have higher initial capacity than electrodes prepared from conventional carbons. |
