锂离子电池Si/C/石墨复合负极材料的电化学性能

Electrochemical Performance of Silicon/Carbon/Graphite Composite Anode for Lithium Ion Batteries

采用热裂解方法,热解分散于聚偏二氟乙烯溶液中的硅和石墨,得到了具有稳定电化学循环性能的Si/C/石墨复合负极材料。透射电子显微镜观察发现,复合材料形貌为无定型碳包裹硅颗粒的核壳结构。通过系统研究不同Si粒径和石墨含量对电极电化学性能的影响,发现Si颗粒粒径越小复合材料电化学循环稳定性能越优越,适当的降低石墨含量有利于电极材料剩余比容量的提高。当Si粒径为50 nm,Si与石墨质量比1:1时,电极材料具有1741.6 mAh/g的首次放电比容量和72.5%的首次库仑效率,60次循环后,可逆比容量保持在820 mAh/g。热解有机物形成碳包覆的结构能有效地改善硅基类负极材料的电化学循环性能。

Silicon and graphite with polyvinylidene fluoride as the matrix was pyrolyzed to obtain the Si/C/graphite composite anode with the stable and excellent electrochemical performance. The morphology of the composite was characterized by transmission electron microscope （TEM）. The result showed that the composite had core-shell structure in which silicon particles were wrapped by the amorphous carbon. The effects of the silicon particle size and the graphite content on the electrode electrochemical performance were investigated systematically. It reveals that the fine size of silicon particles is beneficial to obtain a stable electrochemical performance. The appropriate content ratio of graphite and silicon is necessary to increase the reversible capacity of the composite. When the mass ratio of silicon to graphite is 1：1 and the silicon particle size is 50 nm, the Si/C/graphite composite presents the first discharge specific capacity of about 1741.6 mAh/g and the first coulombic efficiency of 72.4%. The reversible specific capacity still remains 820 mAh/g after 60 cycles. It demonstrates that the carbon-coating structure can be obtained by pyrolyzing the organic matter which will improve the electrochemical performance of the silicon-based anodes effectively.