带状中间相沥青基石墨纤维结构对电化学性能的影响

通过中间相沥青熔融纺丝、预氧化、炭化及石墨化处理制得了带状中间相沥青基石墨纤维。研究了喷丝孔尺寸和纺丝速率对带状石墨纤维横截面碳层片取向和晶体结构的影响，对用作锂离子电池负极材料的带状石墨纤维的电化学性能进行了测试。结果表明：喷丝孔尺寸和纺丝速率对石墨纤维碳层片取向具有显著影响。采用低长宽比的喷丝孔在低纺丝速率下制备的石墨纤维其碳层片取向呈类辐射状，此石墨纤维负极材料的倍率性能较好，在0.1C和1C倍率下其放电比容量分别为336和300 mAh·g^-1，但其循环稳定性较差，在0.1C倍率下循环100次后容量保持率为89.1%；采用高长宽比的喷丝孔在低纺丝速率下制备的石墨纤维其碳层片呈波浪褶皱状且沿平行纤维主平面取向度高，此石墨纤维负极材料的倍率性能相对较差，但其循环稳定性较好，在0.1C倍率下循环100次后容量保持率为98.8%。随纺丝速率的增加，石墨纤维碳层片整体有序度降低，平行纤维主平面取向的碳层片含量减小，由此导致纤维负极材料的可逆比容量下降。

Effects of Structure on Electrochemical Performances of Ribbon-Shaped Mesophase Pitch-Based Graphite Fibers

Ribbon-shaped mesophase pitch-based graphite fibers (MPGFs) were prepared by melt-spinning, preoxidation, carbonization, and graphitization. The effects of the size of the spinneret and spinning rate on the orientation of the carbon layers and crystal structure of the ribbon-shaped graphite fibers transverse section were investigated. The electrochemical performances of the ribbon-shaped MPGFs as anode materials for lithium-ion batteries were tested. The results show that the size of the spinneret and spinning rate significantly affect the orientation of the carbon layers. The carbon layers of graphite fibers that were prepared at a low spinning rate using a spinneret with a low length/width ratio were arranged along the radial direction. These fibers had good rate capability. Their discharge specific capacities at 0.1C and 1C rates were 336 and 300 mAh·g^-1, respectively. However, the fibers showed poor cyclic performance. After 100 cycles at 0.1C rate, the capacity retention was only 89.1%. The carbon layers of the graphite fibers that were prepared at a low spinning rate using a spinneret with a high length/width ratio had a wavy, wrinkled texture and were arranged along the direction parallel to the principal plane of the fibers. These fibers had poor rate capability and excellent cyclic performance. After 100 cycles at 0.1C rate, the capacity retention was 98.8%. Meanwhile, an increase in the spinning rate causes an overall decrease in the order degree of the carbon layers of the graphite fibers, and results in a decrease of the carbon layers being arranged along the direction parallel to the principal plane of the fibers. Both these factors decrease the reversible specific capacity.