Synthesis And Electrochemical Performance Of Zinc Sulfide Anode Material For Lithium-Ion Batteries

With the rapid development of rechargeable lithium-ion batteries, much effort has been focus on investigation of new electrode materials. Carbon materials (theoretical capacity of 372mAh/g) presently used in commercial Li-ion batteries is insufficient to meet the further demand of the new generation of lithium-ion batteries. The search for new anode materials has been motivated by needs for higher energy, improved cycle life and safety. In this paper, we focused on the studies of Zinc-based materials used as anode materials for lithium ion batteries. ZnS/C composites were prepared using liquid homogeneous precipitation method combined with a carbon coating process by high-temperature pyrolysis. The microscopic structure and surface morphology of the prepared ZnS/C composite were analyzed by XRD and SEM. Electrochemical properties of the material were measured by charge-discharge test and cyclic voltammetry (CV). Ex-situ X ray diffraction (ex-situ XRD) technique was applied to analyze the lithium insertion and extraction mechanism of ZnS/C electrode.ZnS nano-particles with diameter of 10-20nm were prepared by liquid precipitation method using ZnCl2?4H2O and Na2S?9H2O as raw materials. Carbon coating was performed at 700oC using sucrose as carbon source. Initial discharge and charge capacities of ZnS/C at the current density of 40 mA g-1 were 1231.8 mAh g-1and 634.7 mAh g-1, respectively. After 100 cycles, the reversible capacity was still maintained at 525mAhg-1, 82.8% of the initial capacity. The nano-ZnS/C material showed a high capacity and excellent cycling stability, which was proved to be a promising anode material for lithium-ion batteries.Mechanism of lithium intercalation and extraction in ZnS/C was suggested. During the Li+ intercalation procedure, Zn was replaced by Li from ZnS and formed Li2S, and then Zn reacted with lithium ion to form Li-Zn alloy. During the Li+ extraction procedure, lithium ion firstly removed from the Li-Zn alloy, and the product Zn reacted with Li2S to form ZnS again. The Li2S formed in the first cycle couldn't fully reverse back, which resulted in a large irreversible capacity.Different ZnS synthesis methods were also compared in this dissertation, the ZnS powder prepared by liquid precipitation method using H2O as the solvent demonstrated the best electrochemical properties. Results of electrochemical measurements indicated that carbon coating technology played an important role in improving the electrochemical performance of ZnS anode.In addition, we explored the synthesis and electrochemical characterization of a novel Sn-ZnS/C composite, based on the knowledge of high theoretical capacity of Sn and outstanding cycling performance of ZnS/C. XRD analysis of the produced material indicated that the high energy milling technology was an effective way for solid-state displacement reaction. The obtained Sn-ZnS/C composite delivered an initial delithiated capacity of 493.5mAh g-1. Further investigation was needed to improve the cycling performance of this material.