Electrochemical Performance Of Pitch-based Carbon Fibers As Anode Material For Lithium Batteries

Pitch-based carbon fibers(PCFs)have a great potential as anode materials for prospective structural lithium-ion batteries(LIBs)due to their suitable mechanical strength and lithium storage performance.But the correlation between microstructure and electrochemical performance is still not clear.My research works have focused on the lithium storage performance of PCFs and the correlation between the fibrous structure and their electrochemical performance.Forthermore,the PCFs between high reversible capacity and excellent cycle stability were obtained by continuously exploring the preparation technology of PCFs.Specifically,the main works and conclousions include the follows parts:(1)Using an isotropic pitch as material,round-shaped SC pitch-based carbon fibers were prepared by melt-spinning technology.The heat-treatment temperature how effects the structure of fibrous transverse section and the sizes of microcrystalline was investigated and the electrochemical performance on corresponding temperature spots was tested.Using a mesophase pitch as material,round-shaped AR pitch-based carbon fibers were prepared by melt-spinning technology.The heat-treatment temperature how effects the structure of fibrous transverse section and the sizes of microcrystalline was also investigated and the electrochemical performance on corresponding temperature spots was tested.During first cycle,the charge capacity and discharge capacity of AR fibers(AR3000)with the graphitization temperature of 3000°C were 373.4 and 319.1mAh/g at 0.1C rate,respectively.The initial coulombic efficiency of AR3000 was 85.5%.Forthermore,the capacity of AR3000 could reach 335mAh/g during cycling process and the capacity retention of the fibers over 100 cycles was 82.2%.The works consider that decreasing capacity of AR3000 can be attributed to the burst of fibers and the exfoliation of carbon layers resulting lithium-ion can not be intercalated to the damaged carbon layers.(2)To further obtain the excellent cycle stability,the works selected the point of spinning rate.When the spining rate was up to 100m/min,the charge capacity and discharge capacity of round-shaped AR graphite fibers were 300.7 and 271.9mAh/g at 0.1C rate respectively during first cycle.The initial coulombic efficiency of the fibers was 90.4% and the capacity retention of the fibers over 100 cycles was 98.6%.The results show that,the disordered carbon layers dispersed the stress toward the core of fibers and maintained the structural completeness of lithium intercalation sites during repeated lithium intercalation process,resulting that the better cyclie stability of round-shaped AR graphite fibers prepared by conctroling a spinning rate of 100m/min was showed.But the lithium intercalation sites of the fibers were decreased by disordered carbon layers and the reversible capacity of the fiber was reduced.(3)Considering the reversible capacity and the better cycle stability can not be possessed as the same time,round spinnerets was replaced by rectangular spinnerets.The electrochemical performance of ribbon-shaped mesophase pitch-based graphite fibers(MPGFs)was tested.When the size of spinnerets was selected at 8×0.1mm,the first discharge capacity of the prepared fiber was 318.2mAh/g at 0.1C rate and the capacity retention of the fibers over 100 cycles was 98.8%.The results show that,the reversible capacity and cycle stability are significantly affected by the orientation of carbon layers and the microcrystalline sizes.