Study On The Formation Of Carbonaceous Mesophase Structures And The Applications Of Thereof Carbon Materials

Carbonaceous mesophase is an important precursor for preparation of carbonmaterials and its structures and post-treatment conditions determine the structures ofthereof carbon materials. Actually, the structures of mesophase-derived carbonmaterial are related to almost all its properties and consequently influence its specificperformance and the final applications. Therefore, it is very meaningful not onlytheoretically but also practically to control the forming structures of carbonaceousmesophase and its development during post treatment. In order to control the structure formation and development of carbonaceousmesophase effectively, the first thing is to make clear of its real evolution process. Tofulfill this point, formation and development process of carbonaceous mesophaseaccording to homogeneous nucleation and heterogeneous nucleation weresystematically studied in the thesis. By paying more attention to the smallcarbonaceous particles obtained during mesophase evolution, "Building fromGranular Basic Units" (BGBU) has been advanced to describe the formation anddevelopment of carbonaceous mesophase. Using this theory, the formation ofmesophase spheres with typical or complex internal structures, nucleation andbuilding role represented by solid particles during mesophase formation and the finalstructures of as-obtained spheres can be successfully predicted. By analyzing thestructure information of mesocarbon microbeads (MCMB) shown by oxidationetching method, the internal structures predicted by BGBU is proven. At themeantime, it is found that the MCMBs heat-treated at different temperatures haveasymmetric carbon structures, which are caused by the inherent formation process ofmesophase spheres, directional development of carbon structure during heat-treatment and small amount of pyrolytic carbon on the surface deposited duringgraphitization. The mesophase-derived carbon materials after heat-treatment at low ormiddle temperatures represent three kinds of lithium ion storage predicted by BGBUand the difference or change of their charge/discharge performance are derived fromthe different structures of mesophase precursors or the changes of lithium storagestructure during heat-treatment. Due to the low graphitization degree particles on thesurface, graphitized MCMB show low charge/discharge capacity and coulombefficiency. However, the electrochemical performance was improved significantlyafter removing these particles by oxidation etching method. The carbon layerstructures and pore structures of MCMB activated by KOH were also investigated. Ithas been found that the specific surface area and microporous content reducedapproximately with the increase of heat-treatment temperature, whereas theircapacitance when used as electric double layer capacitor electrodes doesn't exhibitthis correlation. The MCMB pretreated at 700℃ and then activated by KOH, havingmedium specific surface area and microporous content, shows the highest capacity,the best stability when large current densities are applied and the smallest contactresistance and dispersion resistance in pores. Finally, mesophase pitch-based carbonfoams (MPCF) are manufactured using our patented size-restriction method and theobtained MPCFs are characteristic of uniform pore size and isotropic carbon layerstructure.