The Structural Design And Performance Study Of Molybdenum Disulfide Anode For Li-ion Batteries

With the development of science and technology, portable electronic and wearable electronics have been widely applied in modern society. Among components of these electronics, energy-storage systems, especially, batteries have been more and more important sections to limit the weight, size and working time of those devices. In addition, ever-increasing population in the world leads to soaring demand of transport vehicles. Traditional traffic vehicles use fossil fuels as power source, resulting in serious environmental pollution and unsustainability of energy. The key to solve the problems is to develop high performance batteries, which should display higher energy density, higher power density and longer cycle life and environment benignity. The best choice is lithium-ion battery (LIB), which has been developed and commercialized in last decades. However, the energy density and power density of traditional commercial lithium-ion batteries cannot meet the requirements of some electronics.One important strategy to improve the electrochemical performance of lithium-ion batteries is to promote research and development (R&D) of new electrode materials with high specific energy density, power density, and long cycle life. Graphite-based materials have been widely applied as anode materials for current commercial lithium-ion batteries. Although graphite-based materials present advantages in cost and cyclability, the theory specific capacity of graphite is low, just 372 mA h/g. Therefore, graphite is difficult to meet the needs of the next-generation electrical devices, and it is urgent to develop next-generation lithium-ion battery anode materials.This thesis focuses on transition metal sulfides-molybdenum disulfide (MoS2), which shows the lamellar structure similar to graphite and higher capacity than graphite. However, due to poor electronic conductivity and large volume change during lithium/delithiation process, molybdenum disulfide exhibits poor electrochemical performance. In this thesis, the author studied the relationship between electrochemical properties of carbon-coated molybdenum disulfide electrode material with structures, and carbon weight content. Flower-like molybdenum disulfide with a few layer sheets can be used to limit the size of electrode materials. Moreover, the encapsulation structure molybdenum disulfide embedded into nano-carbon composite material conductive network results in improvement the electrochemical properties of the electrode material.Chapter 1 gives a brief introduction of development history, structure, basic principles, characteristics and applications of batteries, focusing on lithium-ion batteries. Afterwards, the anode electrode materials for lithium ion batteries and the existing problems as well as solutions for improvement in electrochemical performance of anode electrode material have been discussed. Finally, the background and content of this thesis is briefly introduced at the end.Chapter 2 displays a review of the preparation methods and raw materials of the high electrochemical performance molybdenum disulfide electrode material. The equipment used in the characterization of morphology, phase structure, components is also reviewed in this chapter.Chapter 3 shows a strategy to fabricate a flower-like molybdenum disulfide-graphene nanosheets-carbon nanotube (MoS2-GNS-CNT) nanocomposite by a facile hydrothermal process. The nanocomposite can be used as anode material for fast lithium storage. The introduction of a graphene backbone and CNT prevent the growth of MoS2, resulting in the formation of few layered nano-MoS2 (about 5-10 nm). The CNT are intimately embedded in the composites to form highly conductive 3D networks, which serve as a highly conductive substrate leading to the high-rate performance. In addition, CNT in the unique hybrid nanostructure prevent the restacking of GNS. The MoS2-GNS-CNT composite exhibits superior rate capability (300 mA h/g at 20 A/g) and ultralong cyclability (728 mA h/g at 5 A/g after 1000 cycles). We believe that our strategy could be broadly applicable for the preparation of other transition metal dichalcogenide (TMD) materials with great promise for various applications.Chapter 4 gives a simple summary of my work. An analyses of the innovation and the deficiencies of this thesis have been showed. Finally, a simple vision and outlook for the future research work is made.