Preparation And Sodium Storage Of MoS₂-Based Nanocomposites

MoS2,a two-dimensional layered compound,consists that covalently bonded S-Mo-S layers combine together by van der Waals forces.The layer spacing is as high as 0.62 nm,which can facilitate the insertion/extraction of Na+.MoS2 with the theoretical capacity of 670 mAh g-1 is a promising sodium ion battery(SIB)anode material.However,during the charge/discharge process,the MoS2 electrode always suffers from the stacks of sheets causing ion diffusion and electron transport to be hindered,and irreversible electrochemistry,resulting in a poor cycle stability.In this thesis,some effective strategies of S depositing,MoO3 coating,constructing ternary composite materials and regulating crystal architecture are employed to stabilize the cycle performance.Furthermore,the effect of material structure on the electrochemical stability is expounded.A nanoarchitecture of S/MoS2 was constructed by depositing S nanodots on the surface of MoS2 nanosheets in a dual temperature zone tube furnace.S nanodots play an effective anti-blocking agent to alleviate the stacking of MoS2 during the charge/discharge process.When used as anode for SIB,the S/MoS2 electrode delivers a capacity of 498 mAh g-1 at current density of 100 mA g-1,remained capacity of 413.2 mAh g-1 after 100 cycles.Even at higher current density of 500 mA g-1,the electrode capacity retains up to 83.8%after 300 cycles.The MoS2 nanosheets were quenched to prepare ultra-thin MoO3 coated defect-rich MoS2.The unique structure reduces the surface energy of MoS2 nanosheets to prevent the stacking of MoS2,thus achieving a superior cycle life.Further experiments and theoretical calculations show that Na+ can across the MoS2 layer through vacancies rather than only diffusion along the layer to realise a 3D diffusion,thus achieving faster kinetics illustrating the highly reversible capacities of 350 and 272 mAh g-1 at 2 and 5 A g-1 after 1000 cycles.Furthermore,an activated carbon(AC)was employed as a substrate to in-situ syntheses MoS2 nanostructure(MoS2/AC),in which MoS2 is fixed and dispersed on AC.In order to obtain more stable electrochemical performance,the ternary composite materials of S/MoS2/AC and MoO3/MoS2/AC were further constructed by S depositing and MoO3 coating.The S/MoS2/AC electrode can remain a capacity of 191 mAh g-1 after 100 cycles at a current density of 0.5 A g-1.The MoO3/MoS2/AC electrode delivers a capacity of 294 mAh g-1 at 0.5 A g-1.After 100 cycles,the capacity remains 101 mAh g-1.Compared with the MoS2/AC electrode,the depositing and coating strategies can further improve the cycle stability.A grain-like MoS2 particles are prepared by sulphurizing MoO3 in a high concentration of S vapor.The product consists of the MoS2 particles coated by several layers MoS2.This architecture ensures a dispersibility and sufficient space to accommodate volume changes during the charge/discharge process.When used as SIB anode,the electrode can store Na+through reversible intercalation and conversion reactions accompanied with a stable structure.The G-MoS2 electrode can maintain capacity of 312 mAh g-1 after 300 cycles at 0.5 A g-1.