Study On The Preparation And Performance Of SnO₂/C Composite Anode For Li-ion Batteries

Currently, carbonaceous materials are commercially used in lithium-ion batteries due to good safety, stable charge-discharge properties and low-cost. However, their theoretical capacity is only 372mAhg-1, which cannot meet the demand of large electric devices. SnO2, with a high theoretical capacity of 782mAhg-1, is a promising anode material of next generation. But there are severe volume changes during Li-ion insertion and extraction, leading to its fast capacity fading. In this paper, we prepared SnO2 or SnO2/C composite with carbon-coated methods in order to enhance the cycling performance.1) The SnO2/graphite/carbon nanotube(CNT) composite was prepared by high energy ball milling with commercial SnO2, flaked graphite and CNT as raw materials. The results of SEM showed obviously that the size of SnO2 particles decreased to nanometer scale, and were embedded in the graphite matrix.In the meanwhile, CNT distributed uniformly in the composite, forming a good conductive network. The SnO2/graphite/CNT composite exhibited the excellent electrochemical property. The specific capacity was approximately 431mAh/g after 25 cycles and the coulombic efficiency was above 95 percent. Graphite was a buffering material; CNT, a good conductive additive, could store the electrolyte and enhance the destruction-resistant performance of the electrode.2) The SnO2 particles were synthesized by liquid-precipitation, sol-gel and molten salt process. The particles with corresponding methods were defined as L-SnO2, S-SnO2 and M-SnO2. All the diffraction peaks in XRD patterns can be well indexed to powder diffraction standards card. The results showd that the L-SnO2 particles displayed the best cycling performance (262mAh/g after 30 cycles). The regular prism porous structure can cushion the volume expansion.In addition,5%,10% and 15%(wt.) CNT were added as conductive additive for improving the electrochemical performance of L-SnO2. The results revealed that adding of CNT could improve the rate capability to some extent, but large specific surface area caused more irreversible capacity.3) The SnO2/CNT composites with different CNT proportions were prepared by liquid-precipitation method. The composite with molar ratios of Sn:C of 0.5:1 exhibited not only good cycling performance, but also excellent rate capability. The SEM of SnO2 and SnO2/CNT after 30 cycles revealed that there were many cracks on the surface of SnO2, while few cracks could be observed on the surface of SnO2/CNT sample. Besides, the influence of different current collectors (Cu and Nickel foam) was studied. The results indicated that the sample with nickel foam had better cycle life. The improved cycling performance was ascribed to the coarse surface of nickel foam and abundant holes and gaps which consolidated the connection with active materials. Based on the characteristic of volume expansion, designing and modifying the configuration of current collector is an effective way to improve the cyclic stability of tin oxide material.