Investigation On Molybdenum-based And Phosphorus-based Anode Materials For Na-ion Batteries

Rechargeable batteries have been widely used in production and daily life.They can be used as an energy supply system for portable electronic devices,electric vehicles and aerospace.Lithium-ion batteries have attracted great attention due to their high energy density,long cycle life,no memory effect and environmental friendliness.Due to the high cost of lithium and the limitation of lithium reserves on land,it is difficult to be the best choice for long-term development of energy storage system.Therefore,sodium ion battery has become a strong competitor of the next generation of energy storage system due to its rich resource reserves,which has attracted extensive attention of researchers and is considered as a substitute that can meet the demand of large-scale energy storage system.In this thesis,a series of research works have been carried out on molybdenum and phosphorus base anode materials for sodium ion battery.The research contents and results are as follows:By using organic solvent step hydrothermal method is simple and rapid synthetic out with metallic phase 1T Fe_0.015Mo_0.972S₂ anode materials,1T Fe_0.015Mo_0.972S₂ anode materials with larger two-dimensional layer spacing of 0.75 nm were prepared by a simple and rapid one-step solvothermal method,and the corresponding 1T Fe_0.015Mo_0.972S₂ produced the main product of Fe-Mo alloy and S before several cycles of charging/discharging.The polysulfide can be strongly adsorbed on Fe-Mo alloy,which inhibits the dissolution and shuttle effect of polysulfide.The cycle stability of 1T Fe_0.015Mo_0.972S₂ is ensured.1T Fe_0.015Mo_0.972S₂ has excellent electrochemical properties as a anode material for sodium ion batteries,with a capacity of 262 m Ah g^-1 after 100 cycles at a current density of 0.5 A g^-1.This study reveals the electrochemical reaction mechanism of 1T Fe_0.015Mo_0.972S₂ as the anode of sodium ion battery,which is beneficial to the further development of metal sulfide anode materials.MoS₂/MXene composites were synthesized by two steps of organic solvent hydrothermal treatment and high temperature sintering.MoS₂ forms microspheres and inserts into the MXene layer during the hydrothermal process,which can effectively alleviate the volume expansion and poor electrical conductivity of the material caused by the deintercalation of sodium ions.The added surfactant PVP can not only regulate the microstructure of the material,but also act as the binder of MoS₂/MXene composites in the hydrothermal process.After 100 cycles at a current density of 1 A g^-1,the reversible capacity remained at a respectable 202 m Ah g^-1.Using red phosphorus,MXene,carbon nanotubes three kinds of raw materials were prepared step grinding ball P/MXene/CNT anode materials,the introduction of MXene interlayer oxygen formed P-O-C and P-O-Ti keys,P/MXene/CNT composites has solved the MXene low capacity and elemental P volume expansion,poor electrical conductivity,the discharge capacity is 670.9 m Ah g^-1 after 70 cycles at the current density of 0.1A g^-1 and 548.4m Ah g^-1 after 100 cycles at 0.5 A g^-1.This shows that MXene plays a good role in the modification of phosphorus matrix composites.