Study Of The MCMB Prepared By Polymerization-pyrolysis Of Coal Tar Pitch Modified With Formaldehyde

In this paper, coal-tar pitch was polymerically modified with formaldehyde in thepresence of acid catalyst, and then mesocarbon microbeads (MCMB) were prepared bypyrolysis of the polymerically-modified pitch in this paper. The mesophase transformationbehavior of the modified pitch, and the properties and preparation process of the MCMBwere studied, respectively. Lithium-ion battery anode material was prepared from theMCMB by heat-treatment, and the influences of electrochemical performance on thestructure and diameter distribution of the MCMB were investigated.The molecular structures and properties of the polymerized pitch were studied usingFT-IR,1H-NMR, XRD, TG and Viscometer. The results show that polycyclic aromatichydrocarbon of coal-tar pitch happens electrophilic substitution reaction withformaldehyde in the presence of oxalic acid, forming the polymerized pitch with largermolecular weight and thus resulting in an increase in carbonization yield and softeningpoint. Moreover, it has a significant improvement in the heat resistance and rheologicalproperties of the polymerized pitch. The polymerized pitch demonstrates the characteristicsof non-Newtonian fluid behavior, and its viscosity can be easily adjusted by changingmodification process to meet various requirements.The structures and morphologies in the mesophase transformation process wereobserved by FT-IR, SEM, TEM and polarized light microscope. It is found that the MCMBare prepared by condensation reaction. The formation mechanism of the MCMB is that bigparallel planar molecules form the insoluble micro domains, and then carbon black formsthe MCMB’s shell surrounding the insoluble micro domains.The properties and preparation process of the MCMB were studied using SEM, XRD,particle size analysis, and so on. The results show that the different modification processconditions, espeacially heat treatment temperature and time, influence the structures and properties of the modified pitch. The polymerized pitch has carbonization yield of52%-56%and softening point of90℃-96℃, and the resultant MCMB’s yield arrives at17%-32%. Moreover, the carbon black appears to prevent the coalescence and makes theparticle of the spheres smaller, and thus the properties of the MCMB are optimized.The electrochemical performances of the MCMB as anode material for lithium-ionbattery were investigated. The effects of temperature heat treatment and particle size on theelectrochemical performances and cycle performance were studied. The results show thatthe reversible capacity and irreversible capacity of the MCMB decrease with increasingheat treatment temperature and average particle size, while its coulomb efficiencyincreases. It still holds93.5%of first discharge capacity after30cycles revealing goodelectrochemical performances of the MCMB prepared.