Effect Of Graphene Addition On The Formation And Electrochemical Performance Of Mesocarbon Microbeads

Mesocarbon Microbeads(MCMBs)are a new type of carbon materials because of their unique structure,high specific surface area,good chemical stability,electrical conductivity and thermal conductivity.MCMBs have been used as the high-quality precursors for the preparation of high-performance carbon materials and exhibit high application value in many fields.Significantly,the unique spherical structure,the microstructure of parallel stacking of lamellar molecules,excellent electrical conductivity,cycle stability,good rate performance and other characteristics of MCMBs guarantee MCMBs a promising anode material for lithium-ion batteries(LIBs).Graphene is a hexagonal honeycomb structured planar two-dimensional nanomaterial composed of carbon atoms,which has many excellent characteristics such as high electrical conductivity,high thermal conductivity,high specific surface area,high strength and rigidity.Graphene with excellent physicochemical properties has very important application value in high energy density and high power density lithium ion battery anode materials.In this paper,coal tar pitch is used as the raw material,and the thermal polycondensation method is used to explore the effect of the raw material composition on the formation of MCMBs.The rational preparation process is explored by changing the polymerization temperature and soaking time.By adding graphene,the orientation of aromatic molecules in the raw pitch is induced to promote the formation of MCMBs.After carbonization and graphitization of MCMBs,the electrochemical tests as anode materials for LIBs were conducted.In this experiment,the polarizing microscope,SEM,XRD and FTIR instruments were used to test and analyze the morphology and structure of MCMBs,and the electrochemical performance of MCMBs was measured using the battery test system to correlate the relationships between the formation process of MCMBs under different preparation conditions,and the morphology,crystal structure and electrical properties.The experimental results show that the refined coal tar pitch components with low primary PI content and low ash content are more uniform,which is more conducive to exploring the effect of additives on the formation of MCMBs.The polymerization temperature and soaking time have an important influence on the preparation of MCMBs.Increasing the polymerization temperature or soaking time are beneficial to the growth of MCMBs.Without the addition of graphene,MCMBs without fusion were prepared at a constant temperature of 410? for 5 hours possessing the yield of 26.2%.The addition of graphene aligns the aromatic hydrocarbon molecules in RCTP on their sheets,which is beneficial to the formation of MCMBs crystal nuclei and promotes the growth of MCMBs.When the addition amount is 0.1 wt%,the MCMBs show the smallest d002 value and perfect crystal structure.As the increase of graphene addition,the yield of MCMBs shows an increasing trend.Excess graphene hinders the growth and coalescence of MCMBs.When the addition amount exceeds 0.3wt%,aromatic hydrocarbon molecules cannot be effectively stacked together to form MCMBs.The carbonized MCMBs belong to amorphous carbon materials,which have higher specific capacity,but lower first efficiency as anode materials in LIBs.The sample with the graphene content of 0.05wt%exhibits the first efficiency of 69.5%,and the first specific charge-discharge capacity 568.4mAh·g-1 and 395.1mAh·g-1,respectively.The MCMBs obtained by adding graphene are easy graphitizable carbon materials.The graphitized MCMBs with the graphene addition of 0.3wt%have the first charge-discharge specific capacity of 392.2mAh·g-1 and 300.1mAh·g-1,respectively,and the first efficiency of 76.5%.After 20 cycles,the reversible specific capacity 298.5mAh·g-1,and the capacity retention rate is as large as 99.5%.After adding graphene,the graphitized MCMBs also show better rate performance.As the amount of graphene increases from 0.05wt%to 0.5wt%,at different current densities,the average reversible specific capacity of each sample is higher than the sample without graphene.The sample with the graphene content of 0.5wt%can maintain a specific capacity of 156.3mAh·g-1 at a current density of 1A·g-1.