Synthesis Of Nb₂₅/Carbon Composite And Applications In Li/Na Ion Batteries

With the increasingly severe environmental pollution and energy crisis,the development of new energy technologies has received a lot of attention.Energy storage is an important link in energy utilization.Typical energy storage devices include supercapacitors,lithium-ion batteries,and sodium-ion batteries.The anode material is a very important component of these energy storage devices.The anode materials currently widely studied mainly include porous carbon materials and metal oxides.Porous carbon materials have the advantages of good electrical conductivity and large specific surface area,and have been widely used.Metal oxides have high energy density but poor electrical conductivity,and they are usually compounded with porous carbon materials in practical applications.Niobium pentoxide has a unique layered structure.Its empty 4g layer allows lithium ions to be quickly inserted and extracted,but its conductivity is poor,and there are currently few practical applications.Sodium alginate has the property of self-crosslinking with metal ions.In this thesis,a uniformly distributed core-shell structure composite material was prepared by cross-linking sodium alginate and niobium ions,and carbon nanotubes were doped in sodium alginate to prepare Composite material with three-dimensional network structure.The synthesized Nb₂O₅/Carbon materials exhibited excellent electrochemical performance in lithium-ion batteries and sodium-ion batteries,and the main factors affecting the performance of the materials were discussed.The main conclusions are as follows:(1)Cross-linking sodium alginate with niobium ions to obtain a core-shell structure T-Nb₂O₅@C composite material with a porous structure.The diameter of Nb₂O₅ in the composite material is uniform,5-10 nm.The core-shell structure Nb₂O₅@C composite material was used as the anode material for lithium-ion batteries and sodium-ion batteries.The specific capacities of 130.6 and 94.9 m Ah/g were obtained at 0.1 A/g,and they had good rate and cycle performance.(2)T-Nb₂O₅@C/CNTs composite was prepared by doping carbon nanotubes in sodium alginate solution and then crosslinking with niobium ions.The core-shell Nb2O5@C covers the surface of carbon nanotubes,and bonds different carbon nanotubes together to form a unique three-dimensional network structure.The prepared composite materials were tested for lithium storage and sodium storage performance,respectively,having specific capacities of 150.06 m Ah/g and 109.2 m Ah/g at 0.1 A/g,and the capacity retention after 200 cycles was 90.95%and76.84%,And has better rate performance.(3)The effects of doped carbon nanotubes on the microstructure and properties of composites were analyzed.By doping carbon nanotubes,the content of graphitized carbon in the composite material is increased,the comprehensive conductivity of the material is improved,and the rate performance of the material is improved.The unique three-dimensional network structure improves the specific surface area and pore volume of the material,increases the contact area with the electrolyte,effectively reduces the ion diffusion path,thereby improving the specific capacity and rate performance of the material.Larger pore volume and the like also reduce the strain on the material during multiple cycles of charge and discharge,thereby exhibiting better cycle performance.In summary,in this study,Nb₂O₅/Carbon composites were prepared by the self-crosslinking properties of sodium alginate,and the microstructure of the composites was controlled by doping.The prepared materials were further applied in the field of energy storage,and the influence of microstructure on energy storage performance was studied,which provided a reference for the subsequent preparation of nanomaterials and the regulation of microstructure.