热处理对富氮碳纳米纤维结构及储锂性能的影响

以聚丙烯腈(PAN)为原料,经静电纺丝、稳定化和碳化,制备了碳纳米纤维(CNFs)。系统地研究了氮的种类及含量对锂离子电池(LIBs)中Li+的储存性能和负极容量的影响。碳化过程中纤维从无定形碳向石墨化碳结构转变,含氮官能团减少,结构的变化对Li+在CNFs电极中的存储位置有很大的影响。结果表明,Li+不仅可以存储在石墨化碳层之间,还可以存储在氮功能化引起的缺陷部位,后者主要是由于碳材料的氮掺杂而使LIBs的电化学性能改善。碳化温度为600℃时,可以产生足够高的氮含量,从而提高电极的容量。在电流密度为0.1 A·g^-1时,循环200次之后比容量高达560 mAh·g^-1,即使在1 A·g^-1的高电流密度下,循环1000次比电容量仍然保持在200 mAh·g^-1。

Effect of Heat Treatment on Structure and Lithium Ion Storage Properties of N-Rich Carbon Nanofibers

Carbon nanofibers(CNFs)were prepared from polyacrylonitrile(PAN)via electrospinning followed by stabilization and carbonization.The morphology and structure of the carbon nanofibers were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),Raman spectroscopy,Fourier transform infrared spectroscopy(FTIR),and X-ray photo-electron spectroscopy(XPS).The electrochemical properties were investigated as anode material in lithium ion batteries(LIBs).A systematic study was made to confirm the effect of the nitrogen species on the performance of lithium ion storage and the capacities of anodes in LIBs.It is noticed that the structure change has a great influence on the storage position of lithium ion in CNFs electrode.The results showed that lithium ions can be stored not only between the graphitized carbon layers,but also in the defects caused by the functionalization of nitrogen,the latter was mainly because the improvement of the electrochemical performance of LIBs due to the N-doping of carbon materials.There is a strong correlation between the atomic structure,with lithium ion storage behavior and electrochemical properties of anode materials.It is revealed that thermal annealing had an important effect on the atomic structure and morphology of CNFs.A high temperature treatment promoted graphitization and improved electrical conductivity through the growth of aromatic groups.During the transition from amorphous carbon to graphite structure at high temperature,defects and heteroatoms were removed with the decrease of nitrogen contents.Therefore,CNFs obtained at high carbonization temperature may have high lithium ion storage capacity between graphene layers,but it failed to provide attractive capacity due to low nitrogen content.An optimized carbonization temperature of 600℃was identified,the electrode gave rise to a sufficiently high nitrogen content and thus a high capacity about 560 mAh·g^-1 after 200 cycles at the current density of 0.1 A·g^-1,the specific capacity at the high current density of 1 A·g^-1 even still remained 200 mAh·g^-1 after 1000 cycles.