Controllable Synthesis Of Two-dimensional Layered Molybdenum-based Materials And Electrochemical Performance As Anode Materials Of Lithium Ion Battery

With the increasingly severe environmental problems,lithium-ion batteries with environmentally friendly,high energy density and high operating voltage have been widely studied and developed.However,electrode materials that can achieve high capacity,long life,and rapid charge and discharge are still hotspots and difficulties.The two-dimensional layered mesoporous electrode material also has many advantages.On the one hand,the two-dimensional layered conductive layer can effectively improve the conductivity of the material.On the other hand,the mesoporous structure can reduce the solid state transmission distance?Li⁺and e^-?.While,molybdenum-based materials have the advantages of variable structure,abundant types,and high theoretical specific energy.Therefore two-dimensional layered mesoporous molybdenum-based electrode material is one of the potential candidate anode materials for the next generation of high performance lithium ion battery.The innovation of this dissertation lies in the ingenious combination of layered graphene with molybdenum-based nano-electrode material through a novel synthesis method,which has the advantages that the nanomaterial effectively shortens the transmission path of lithium ions and electrons.Is also favorable for charging and discharging at high current density.Furthermore,it can increase the contact area between the electrode and the electrolyte and easing the volume change caused by the insertion and extraction of lithium ions during cycles.The high surface energy or defect energy of nanomaterials significantly affects the theoretical voltage of the battery,making the electrode reaction possible within a wide voltage window.The addition of graphene plays important roles,namely,to increase the electronic conductivity of the active material and stabilize the structure of the active material.The addition of graphene also maintain electrical contact between the active materials and between the active material and the current collector.This subject takes the molybdenum-based electrode material as the research object and intends to solve the following scientific problems.Firstly,the construction of a two-dimensional layered molybdenum-based material system and its feasibility as a negative electrode material for lithium ion batteries.Secondly,the improvement of electrochemical properties for 2D layered molybdenum-base materials as anode materials for lithium-ion batteries.Thirdly,the mechanism of electron transport in 2D layered molybdenum-based electrode materials are investigated.In the first part of this thesis,taking the 2D layered meso-MoO₂/rGO electrode material as the initial research target,using KIT-6/r GO as a template and ammonium molybdate as a precursor.Nanocasting method was regarded as the efficient method for the synthesis of meso-MoO₂/rGO electrode materials.By adjusting the experimental conditions,the electrochemical properties of meso-MoO₂/rGO electrode material and bulk MoO₂ electrode material were studied and the charge-discharge mechanism was discussed.The second part of this dissertation is based on the first part of the work.During the synthesis process of meso-MoO₂/rGO electrode material,glucose was added and used as the carbon source.By controlling the experimental conditions and the calcination temperature,the meso-MoO₂-Mo₂C/rGO electrode material was obtained and the influence of Mo³⁺/Mo²⁺on the conductivity and electrochemical properties of the MoO₂-Mo₂C heterojunction was discussed.In the third part of this dissertation,diammonium hydrogen phosphate was used as the phosphorus source to obtain the meso-MoP/rGO electrode material by controlling the synthesis conditions.On this basis,an improved experiment was also performed using sodium hypophosphite as the phosphorus source.Under nitrogen protection,the MoP-MoS₂/rGO electrode material was obtained by controlling the phosphating time and temperature,and the influence of the Mo-P bond on the electrochemical properties of the material was also investigated.The fourth part of this dissertation is to treat the meso-MoO₂/rGO electrode material in ammonia gas atmosphere,and obtained MoN@MoO₂/rGO electrode material by controlling the treatment temperature and time.On the basis of this,an improved experiment was also carried out.The ethidene diamine and dopamine were used to modify the KIT-6/rGO template.The nitrogen-doped meso-N-MoS₂/rGO electrode materials were obtained.The effects of nitrogen on the electrochemical properties of the materials were discussed.In the fifth part of this thesis,different selenium additional methods were used.Sulfur powder,thiourea and selenium powder was used as the sulfur source and selenium source respectively.By controlling the content of selenium powder,different selenium doping amounts of meso-MoS₂/rGO electrode were synthesized.Through the systematic test of the synthesized materials,the influence of the addition of selenium on the electrochemical properties of the MoS₂ electrode material was studied,and the influence mechanism was discussed.