Preparation And Electrochemical Performance Of Mesocarbon Microbeads By Emulsion Method From Coal Tar Pitch

Mesocarbon microbeads（MCMB）are a kind of liquid beads prepared from polycyclic aromatic hydrocarbon molecules in the process of liquid phase carbonization.It has the stable graphitizable carbon layer structure,high specific surface area and chemical stability.Thus,it is widely applied in many fields,such as:high performance liquid chromatographic column packing,super-high surface activated carbons and lithium-ion battery.MCMB is considered as a promising anode materials for lithium-ion battery by the virtue of their smooth discharge voltage platform,high discharge capacity.To further promote these performance as lithium-ion battery anode materials,much research is focused on controlling their regular morphology and uniform particle size distribution.The preparation method of MCMB has a great influence on their morphology.The traditional methods to prepared MCMB include polycondensation,emulsion and suspension approaches.These methods have advantages and disadvantages.Polycondensation method has been industrialized at present,but the products can not be separated easily.Emulsion method for the selection of raw materials is relatively harsh.In this work,we combine polycondensation with emulsion.The medium coal tar pitch is used as the raw materials to prepare MCMB in one step process.In order to obtain MCMB with uniform particle size distribution,we employ some suitable additives into the reaction system.We can get the optimal conditions to prepare MCMB by changing temperature,time and the stirring rate.Through adding suitable surfactants and additives,we can obtain MCMB with uniform particle size distribution and promote the yield of MCMB.The morphology and structure of MCMB are characterized by using metallographic microscope、SEM、FTIR and XRD measurement.The electrochemical properties are characterized by cyclic voltammetry test,constant current charge and discharge test.The pitch powder and silicone oil are mixed in the ratio of 1g:20ml.In the range of 350 ℃ to 500 ℃,as the temperature increases,the degree of polycondensation of the pitch continues to increases,and when the temperature is too high,the phenomenon of fusion occurs;When the temperature is up to the reaction temperature,we need to keep heating for a while.With the prolongation of time,the pitch droplets tend to be spherical shape and gradually grow larger.The sample with a holding time of 4 hours has a better appearance.Sodium dodecylbenzensulfonate（1 wt.%）is added into the reaction system as surfactant.The average particle size of the sample is 20.554 um,the particle size mainly locates at 15um to 25 um.The yield of the microbeads increases from 32.65%to 82.71%.In order to get more regular morphology,the carbon black,carborundum and graphite are added into the reaction system as the additives.These samples exhibit a better result.The electrochemical performance of these samples are tested.The sample prepared by adding 1wt.%graphite has a better electrochemical performance.The initial discharge capacity is 422 mAhg^-1 with the reversible capacity of 359.4 mAhg^-1 and the first efficiency of 85.15%.After 50 cycles,the capacity retention rate is 88.91%.At a current density of 1 Ahg^-1 and 2 Ahg^-1,the discharge capacity of this sample are 283.6 mAhg^-1 and 203.6 mAhg^-1,respectively.