Synthesis And Electrochmmical Performance Of M_xS_y(M=Mo,Ni) For All-solid-state Lithium Battery

Graphite cannot meet the development of lithium-ion battery in furture due to its limited theoretical capacity. In recent years, metal sulfides have been extensively investigated as anode material in the merit of high capacity and energy density. In this thesis, MoS2 and NiS were synthesized by hydrothermal method and solvothermal method. The structure, morphology and electrochemical performance of the synthesized materials were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS) and the constant current charge-discharge tests. The results are listed as follows:Firstly, a series of MoS2 nanoflowers with different interlayer spacing ranged from 0.63 nm to 0.70 nm were synthesized with a hydrothermal method. The effect of interlayer distances on the electrochemical performances was studied. The results showed that the MoS2 with optimized interlayer distance of 0.65 nm and good crystallinity, appropriate surface area and defects as well as thickness of nanosheets exhibit the highest lithium storage capacity and the best rate capability. It showed a high discharge capacity of 814 mAh·g-1 at 0.1A·g-1 after 50 cycles and as high as 651.7 mAh·g-1 and 551.2 mAh·g-1 at 1 A·g-1and 2 A·g-1 respectively.Secondly, H2C2O4 was used to modify MoS2 in the hydrothermal process. The results indicate that the prepared MoS2 nanosheets turn thinner, the nanoflower become fluffy and the electrochemical performance was significantly improved. It showed a high discharge capacity of 987 mAh·g-1 at 0.1A·g-1 after 50 cycles and as high as 811 mAh·g-1and 693.4 mAh·g-1 at 1A·g-1 and 2 A·g-1 at 25 oC respectively. What’s more, MoS2/CNTs nanocomposites were also prepared by hydrothermal method, and the electrochemical performances were also significantly improved.Thirdly, the effect of different binders, i.e. PVDF, CMC, PAA, on the electrochemical performances of MoS2 electrodes was investigated. The results showed that the polymer binder has a great impact on the electrochemical performances. The MoS2 electrode with PAA binder exhibited the best electrochemical performances, showing a high discharge capacity of 989.9 mAh·g-1 at 0.1 A·g-1 after 50 cycles and as high as 819.6 mAh·g-1and 759.6 mAh·g-1 at 1A·g-1 and 2A·g-1.Furthermore, the electrochemical performances of MoS2 prepared by hydrothermal method at the optimized temperature were preliminary studied in the all-solid-state lithium battery with Li10GeP2S12 as the solid state electrolyte. It showed a discharge capacity of 305.3 mAh·g-1 for the first cycle and 27.3 mAh·g-1 for the tenth cycle at 0.1mA. After it was annealed at high temperature in argon atmosphere, the electrochemical performance was not improved.Finally, we synthesized nanorod-like NiS by solvothermal method and studied the electrochemical performance in the all-solid-state lithium battery with Li10GeP2S12 as the solid state electrolyte. It showed a discharge capacity of 350 mAh·g-1 after 5 cycles at 0.1mA.