Studies On Nano ZnS/C Composite As Anode Materials For Lithium-ion Batteries

Batteries with higher capacity, longer life, lower pollution is in demanding, especially anode materials better than commercialized graphite in rate capability and low temperature performance.ZnS/C composites were synthesized by a combined precipitation with carbon coating method from ZnCl₂ and Na₂S. Morphology and structure of the as-prepared ZnS/C composite materials with carbon content of 4.6 wt%, 9.3 wt% and 11.4 wt% were characterized using TEM and XRD technique. TEM observation demonstrated that the ZnS/C (9.3 wt% C) composite showed excellent microstructure with 20–30nm ZnS nanoparticles uniformly dispersed in conductive carbon network. The composite is forming good wurtzite structure.We test the electrochemical performance of the composite through constant current charge-discharge test, cyclic voltammetry etc. It showed that the ZnS/C (9.3 wt%C) composite presented superior performance with initial charge and discharge capacity of 1021.1 and481.6 mAh/g at a high specific current of 400 mA/g, after 300 cycles, the discharge capacity of ZnS/C electrode still maintained at 304.4 mAh/g, with 63.2% of its initial capacity. The rate capability and low temperature performance of the ZnS/C (9.3 wt% C) composite were compared with commercial CMS anode. The results showed that the ZnS/C (9.3 wt%) composite exhibited much better cycle capability and low temperature performance than CMS anode. Under 800 mA/g the material discharge capacity still reached reached 235.2 mAh/g. At low temperature, the CMS anode displayed a discharge capacity less than 100 mAh/g. However, the ZnS/C anode delivered 268 mAh/g at 0℃and 207 mAh/g at ?20℃, which were 74.4% and 57.5% of the capacity at 20℃.The phase change of the ZnS/C electrode at different discharge states is measured by in situ XRD technique in order to clarify the lithium insertion–extraction mechanism. During discharge, lithium ion embedded and zinc will gradually come out to generate Li_xS, eventually the composite completely transformed to Li₂S, metal zinc, and Li_xZn. The process is contrast on the lithium extraction procedure during charging, lithium ion removed from Li_xZn alloy and Li₂S. the peaks of Li_xZn alloy disappeared and the peaks of ZnS are detected with the increasing of the discharge potential, ZnS is re-generated partly.Moreover, we synthesized ZnS/ppy materials and tested its performance as ppy has good conductivity. We found it deserves further study. After all, it can be concluded that ZnS/C composites will be a promising anode active material for rechargable lithium ion batteries application.