Synthesis Of MoS₂and Its Electrochemical Performance As Anode Material For Lithium-ion Batteries

Lithium ion batteries (LIBs) have been widely used in portable electronic devices for itshigh energy density, green and durability. They have attracted significant attentions as themost promising power sources for electric vehicles (EVs). As for the anode materials in LIBs,graphite has been widely commercialized due to its natural abundance, flat potential profileversus lithium, high coulombic efficiency and structural stability during cycling. However, itcannot fully meet the energy density requirement in EVs due to its relatively smalltheoretical specific capacity (372mAh/g). Therefore, alternative anode materials with higherspecific capacity and good cycling performance are desirable for LIBs.Molybdenum disulfde (MoS2), a typical transition metal dichalcogenide with uniquesandwich structure, has shown potential applications in the fields of lubrication, catalysis,hydrogen storage, and so on. The layered structure of MoS2enables easy intercalation of Li+,without obvious increase in volume. In this thesis, we focused on the studies of MoS2usedas anode material for lithium ion batteries. A facile process was developed to synthesizehierarchical MoS2in the basic solution via a hydrothermal route, the influence ofhydrothermal preparation parameters on the material properties and the morphologyevolution of MoS2were systematically investigated. We also explored the relationshipbetween the microstructures and electrochemical performances of MoS2.MoS2was synthesized by employing ammonium heptamolybdate and thiourea asstarting materials and then post-annealing in N2atmosphere at450°C for5h. Themorphologies of the MoS2products can be tuned from the porous flowers to the densespheres by addition of NaOH. Experimental results show that the MoS2products have goodcrystallinity. The formation mechanism of the MoS2is proposed by that the dense MoS2spheres are evolved from the porous MoS2flowers through growing along the <00l>direction of the nano-sheets. Based on the growth mechanism, the microstructure of MoS2 can be successfully controlled by adjustment of S/Mo ratio or addition of surfactant in therecipe.Electrochemical measurements demonstrate that the flower-like MoS2shows betterelectrochemical performance than MoS2spheres as anode materials for Li-ion batteries,which delivers a high reversible capacity of900mAh/g at a current density of100mA/g.Even at a high current density of1000mA/g, the specific capacity of the flower-like MoS2retains at800mAh/g. EIS analysis confirms the high conductivity of flower-like MoS2particles, which greatly enhances electrochemical reaction kinetics. The excellentelectrochemical performance of flower-like MoS2particles with micron size is attributed tothe hierarchical structure made up of nanosheets. Our results prove that MoS2withhierarchical structure holds promise as anode material for high-performance LIBs.In addition, a series of molybdenum disulfide composites, such as MoS2/C andMoS2/PANI were also synthesized and studied.