Preparation And Mechanism Of MoS₂/MoO₂/carbon Nanocomposite Electrode Materials

Molybdenum sulfide?MoS₂?belongs to transition metal chalcogenides?TMCs?,which has a graphite-like structure with a d-spacing of 0.62 nm and high theoretical capacity(670 mAh g^-1).It is considered to be a very promising anode material.However,the restacking of 2D nanosheets is inevitable,which limited the practi cal applications.The low conductivity leads to significant capacity decay during the cycling process.These problems limit the MoS₂ further application in the energy storage system.Generally,the strategy of solving those problems is growing MoS₂ on the surface of substrates via a composite method.In this thesis,we employ a series of carbon materials as substrates for MoS₂ by an in-situ synthesis technology.Moreover,the relationship among structure,composition and performance have been investigated.?1?The effects of the atmosphere on the pyrolysis products of ammonium molybdate was investigated.The results indicate that the products were MoO₃ and Mo₄O₁₁ when the Ar gas flow rate was 150sccm,the product became a mixture of MoO₃,Mo₄O₁₁ and a small amount of MoO₂ when the flow rate reduced to 125 sccm.When the flow rate transfer to 50 sccm,the products became a mixture of MoO₂and a small amount of Mo₄O₁₁.At the flow rate reached to 0 sccm,the pure MoO₂ was obtained.This method eliminates the potential safety hazard of employing Ar-H₂ mixed gas to reduce MoO₃ during the preparation of pure phase MoO₂ in the laboratory.Then,the MoO₂@MoS₂ nanomaterials with 3D structure are constructed through the reduction reaction of MoO₂ and S powder.The MoO₂@MoS₂architectures with the optimized composition of 91%MoS ₂ and 9%MoO₂ show a reversible capacity as high as 1167 mAh g^-1 at the second cycle,remaining the capacity 1016 mAh g^-1 after 200 cycles,which is attributed to the unique 3D architectures composed of hundreds MoS₂ nanosheets and fixed by MoO₂ particles with high electric conductivity,ensuring the MoS₂ structural stability,relieving the volume expansion of MoS₂ after cycling.?2?The MoO₂ was fixed with rGO,and MoO₂/rGO with honeycomb structure was prepared as the electrode material for lithium ion batteries?LIBs?.The MoO₂/rGO honeycomb exhibits the capacities as high as 1128,759,723,and 673 mAh g^-1 at the current density of 0.1,0.2,0.5,and 1.0 A g^-1 after 100 cycles,respectively.A preform-in situ method is employed to synthesize MoS₂ anchored on rGO flexible supports.The MoS₂/rGO delivered a high reversible specific capacity of 930 mAh g^-1 at 100 mAh g^-1.At a high current density of 1000 mA g^-1,the MoS₂/rGO electrode showed favorable cycling stability of 786 mAh g^-1 after 1000 cycles.After being assembled in the MoS₂/rGO//LiCoO₂ full-cell,the combination achieves a maximum energy density of 208 Wh kg^-1 at the power density of 220 W kg^-1.Even at the power density of 1910 W kg^-1,it displays a minimum energy density at 157 Wh kg^-1.?3?The MoS₂/MoO₂/three-dimensional carbon nanocomposites were prepared by adjusting ratios of ammonium molybdate and pomace carbon.By comparison,when the ammonium molybdate content in the preform is decreased?ammonium molybdate:pomace carbon=10:1?,the initial discharge capacity is as high as 1100 mAh g^-1,and the capacity is stable at 800 mAh g^-1 after 5 cycles.After 100cycles,the capacity remains 800 mAh g^-1.When the MoO₂:pomace carbon=10:1inthepreform,thepreparedMoS₂/MoO₂/three-dimensional carbon nanocomposites have an initial discharge capacity of 1295 mAh g^-1,exhibit the discharge capacity 860 mAh^-1after 2 cycles,and remain stable at 815 mAh g^-1.