Preparation Of Modified Mesophase Pitch By Co-thermopolymerization Of Naphthalene Pitch & C₉ Resin And Its Derived Carbon Materials

Mesophase pitch that it's one of excellent precursors for preparing carbon fibers and needle coke determines the structure and preformance of derived carbon materials.Many scholars had carried out lots of researches about frontier exploration,theoretical basis and application on carbonaceous mesophase at home and abroad.There were some studies shown that the structure and performance of mesophase pitch could be controlled by co-thermopolymerization,however,the systematicness and practicability of which need to be consummated.This research aims to investigate the effects of precursor structure on the formation and development of carbonaceous mesophase.It will be achieved in this work that controllable synthesis of mesophasee pitches with specific composition,texture and physical properties through co-thermopolymerization of naphthalene pitch and C₉ resin,and the preparation of spinnable mesophase pitches with modified sturacture and properties.Using these modified mesophase pitches as raw materials,It could be obtained that high-performance pitch-based carbon fibers and various structural pitch-derived coke used to evaluate its electrical performance as lithium ion anode material.The main contents and conclusions are summarized as follows:1.Based on the studies about the formation and transformation behavior of liquid crystal mesophase for several typical carbonaceous materials heat treatment at400?450? for 4 h in nitrogen atmosphere,raw materials which possess alkyl side chains,low softening point and molecular weight showed a relatively high reactivity and the chemical reaction processes were difficult to control,which resulted in a low yield of mesophase pitch with a disorder molecular orientation.The optical texture of mesophase pitches were mostly mosic.In contrast,raw materials with suitable softening point and molecular weight,high molecular planarity as well as relatively adequate reactivity,were benefit to the development of liquid crystalline mesophase.The yield and molecular order degree of mesophase pitch were relatively high,and the main optical texture of which were streamline.Based on the characteristics of naphthalene pitch?e.g.,it was difficult to form mesophase sphere in the early stage of thermal polymerization and its large molecules were stable owing to the lack of side chains,resulting in a difficulty in the subsequent oxidative stabilization?,the various textural mesophase pitches ranging from wide area and stream-line to mosaic type could be prepared by co-thermal polymerization of C₉ resin and naphthalene pitch at430? under 1 MPa in nitrogen atmosphere.The formation rate of mesophase was improved obviously with the addition of a small amount of C₉ resin.As the content of C₉ resin increased,the thermal polymerization rate accelerated,and the content of alkyl side chains and softening point of mesophase pitch significantly increased,but the carbonization yield,anisotropic content,aromatics and molecular order degree of mesophase pitch reduced.2.The spinnable mesophase pitch with?95 vol%anisotropy content and?270? softening point was prepared through thermal polymerization of 5wt%C₉ resin and naphthalene pitch in order to research on the accelerating oxidative stabilization of pitch fibers.C₉ resin possessed low molecular weight,alkyl side chains and relatively high reactivity.The addition of C₉ resin in the naphthalene pitch could improve the formation rate of the anisotropy in thermal polymerization system,which leads in the introduction of certain alkyl structure into the structure of mesophase molecules,so as to reduce its melt viscosity,and improve the spinnability and preoxidation capability of mesophase pitch.Raw pitch fibers prepared with modified mesophase pitch could obviously shorten the pre-oxidation time and complete the oxidation stabilization ahead of 4 h at 240? in air atmosphere,compared with that of unmodified raw fibers.The tensile strength of carbon fibers prepared with modified mesopase pitch was 1.2GPa,which improved slightly than that of the unmodified carbon fiber?1.1 GPa?after carbonization at 1000?.The axial electrical resistivity of graphite fibers prepared with modified pitch was 2.0 x10^-6?·m at room temperature,the axial thermal conductivity value of modified graphite fibers calculated by their electrical resistivity was 677 W·m^-1·K^-1,which enhanced significantly than that of unmodified graphite fibers(3.2 x10^-6?·m.and 473 W·m^-1·K^-1)after 3000? graphitization.3.Various structural coke could be obtained from different textural mesphase pitches after heat treatment at 900? and 2800? for the evaluation on the electrochemical performance of coke as lithium ion cathode materials.With the increase of C₉ resin contents,the structure of coke changed from streamline to mosaic,and the molecular order degree of which became worse.After 900?carbonization and 2800? graphitization,the incorporation of C₉ resin with a proper content??10wt%?could improve the microcrystalline development of coke.With the increase of heat treatment temperatures,the carbon layers in the coke became regular,the defects decreased and the microcrystalline size increased.The cycle stability and the first charge/discharge efficiency of coke as the cathode material in the Li-ion battery were improved.After graphitization treatment,the highly oriented coke had a high graphitization degree and a poor battery rate performance.The coke modified by 40wt%C₉ resin had the appropriate graphitization degree and carbon layer orientation,which achieved the relatively stable cycling performance,low impedance and high rate performance.