硅/碳复合材料的高温热解法制备及其电化学性能

采用高温热解方法成功地合成了高容量硅/碳复合负极材料.通过X射线衍射分析、热重分析、扫描电子显微镜观察、透射电子显微镜观察、恒电流充放电测试、循环伏安法等手段研究了复合材料的性能.结果表明：硅/碳复合材料由Si、C以及少量SiO2组成；硅/碳复合材料中碳的质量分数约在39%左右；经电化学性能测试,在电流0.2 mA下,该硅/碳复合材料首次充电容量768 mAh·g-1,首次库仑效率75.6%,70次循环后可逆比容量仍为529 mAh·g-1,平均容量衰减率为0.44%.这些性能改善归因于硅/碳复合材料中碳的引进,硅表面存在的碳涂层提供了一个快速锂运输通道,降低了电池的阻抗并且充放电过程中稳定了电极的组成.

Synthesis and electrochemical properties of silicon/carbon composites prepared by high temperature pyrolysis

Silicon/carbon composites as anode materials for lithium batteries with high power capacity were synthesized by a high temperature pyrolysis method. The performances of the silicon/carbon composites were investigated by X-ray diffraction, thermogravi-metric analysis, scanning electron microscopy, transmission electron microscopy, galvanostatic cell cycling, and cyclic voltammetry. It is found that the silicon/carbon composites consist of silicon, carbon and few silicon dioxide phases, and the carbon content is about 39%. Electrochemical cycling tests of button cells show that the specific capacity is far more than that of carbon materials. The initial charge capacity of the silicon/carbon composites is 768 mAh·g-1 at a current of 0. 2 mA and the initial coulombic efficiency is 75. 6%. After 70 cycles the reversible specific capacity is 529. 0 mAh·g-1 and the average capacity deterioration rate of each cycle is 0. 44%. These improvements can be attributed to the introduction of carbon in the Si/C composites and carbon coatings on the Si surface, which provide a rapid lithium transport pathway, reduce the cell impedance and stabilize the electrode structure during charge/discharge cycles.