Li Baoliu, Guo Jianguang, Huang Jiajun, Xu Huitao, Dong Zhijun, Li Xuanke
College of Materials Science and Engineering, Hunan University, Changsha 410082, China.
School of Chemistry and Chemical Engineering, Wuhan University of Science and Technology, Wuhan 430080, China.
Materials (Basel). 2020 Apr 20;13(8):1933. doi: 10.3390/ma13081933.
In this study, three kinds of round-shaped pitch-based graphite fiber with different microstructural features (crystallinity and carbon layer orientation) were fabricated by melt-spinning, preoxidation, carbonization and graphitization. The morphology, crystalline size and carbon layer orientation of carbon fibers from different pitch precursors and spinning rates were characterized through X-ray diffraction, scanning electron microscopy and transmission electron analyses. The correlation of the electrochemical performance and microstructure of graphite fibers as anode materials for lithium-ion batteries was investigated. The results suggest that large-diameter anisotropic graphite fibers (L-AF3000) with a radial texture of the transverse section are more favorable for lithium intercalation storage. The discharge capacity of L-AF3000 is 319.1 mAh∙g at 0.1 (current density). Nevertheless, the capacity drops to 209.9 mAh∙g at a high current density of 1 , and the capacity retention is only 82.2% over 100 cycles at 0.1 . Small-diameter anisotropic graphite fibers (S-AF3000) with a spiral-shaped wrinkle texture of the transverse section possess discharge capacities of 284.1 mAh∙g at 0.1 and 260.2 mAh∙g at a high current density of 1 Meanwhile, the best capacity retention of the fibers is 101.6% over 100 cycles at 0.1 . The results suggest that the disordered carbon layers in S-AF3000 can retain the structural integrity of fibers as anode material for lithium-ion batteries and thus obtain excellent cycle stability. In addition, larger crystalline sizes of fibers correspond to higher discharge capacity, and a smaller diameter is beneficial to the fast insertion and extraction of lithium-ion in fibers.
在本研究中，通过熔融纺丝、预氧化、碳化和石墨化制备了三种具有不同微观结构特征（结晶度和碳层取向）的圆形沥青基石墨纤维。通过X射线衍射、扫描电子显微镜和透射电子分析对不同沥青前驱体和纺丝速率的碳纤维的形态、晶体尺寸和碳层取向进行了表征。研究了石墨纤维作为锂离子电池负极材料的电化学性能与微观结构之间的相关性。结果表明，具有横向径向纹理的大直径各向异性石墨纤维（L-AF3000）更有利于锂嵌入存储。L-AF3000在0.1（电流密度）下的放电容量为319.1 mAh∙g。然而，在1的高电流密度下，容量降至209.9 mAh∙g，在0.1下100次循环后的容量保持率仅为82.2%。具有横向螺旋形皱纹纹理的小直径各向异性石墨纤维（S-AF3000）在0.1下的放电容量为284.1 mAh∙g，在1的高电流密度下为260.2 mAh∙g。同时，这些纤维在0.1下100次循环后的最佳容量保持率为101.6%。结果表明，S-AF3000中无序的碳层可以保持纤维作为锂离子电池负极材料的结构完整性，从而获得优异的循环稳定性。此外，纤维较大的晶体尺寸对应较高的放电容量，较小的直径有利于锂离子在纤维中的快速插入和脱出。
