Controllable Preparation,Structural Regulation And Electrochemical Performance Of Low-dimensional Metal Vanadate

At present,the commercialization of lithium-ion batteries has achieved great success,and at the same time,it consumes a large amount of lithium resources,which causes the cost of lithium to rise,further restricting the application of lithium-ion batteries in large-scale energy storage facilities.A new battery system with low cost and excellent performance is imperative;compared with lithium-ion batteries,sodium-ion batteries not only have the same working principle but also relatively low cost,and have become an important alternative technology for lithium-ion batteries in large-scale energy storage facilities..In addition,the water-based zinc ion battery has a high safety factor and relatively low cost,and has gradually become a research hotspot,and is also expected to be applied to large-scale energy storage facilities.The main content of this thesis has three parts.Fisrtly,3D interconnected NH₄Fe_0.6V_2.4O_7.4@C nanocomposite were synthesized by a facile hydrothermal method.Its structure and morphology as well as sodium storage properties were investigated.Secondly,ultralong NH₄V₃O₈ nanobelts was obtained via a facile hydrothermal method.Its electrochemical properties were evaluated as a cathode material for SIBs.Finally,using the hydrothermal-solid phase two-step method,we first prepared the Rb⁺intercalated Na_1.25V₃O₈ one-dimensional material,which was used as the positive electrode material of Zn-ion battery.A novel 3D interconnected NH₄Fe_0.6V_2.4O_7.4@C nanocomposite was in-situ synthesized through a facile hydrothermal reaction at low temperature（98℃）,and the electrochemical performence was investigated as a cathode for sodium-ion batteries（SIBs）for the first time.Under the intercalation of Fe³⁺and carbon-coating,as-prepared samples turned to be 3D interconnected structures,which were composed of NH₄Fe_0.6V_2.4O_7.4nanoparticles and the carbon chains.The 3D interconnected NH₄Fe_0.6V_2.4O_7.4@0.5wt%C nanocomposite exhibits a high discharge specific capacity of 306 mA h g^-1 at the current density of 20mA g^-1 and a high-rate capacity of 130 mA h g^-1 at 0.4 A g^-1.The results of EIS and ex-situ SEM indicated that 3D interconnected NH₄Fe_0.6V_2.4O_7.4@0.5wt%C nanocomposite possesses good electrical conductivity and structural stability.The ex-situ XRD results suggest that NH₄Fe_0.6V_2.4O_7.4@0.5wt%C undergoes a reversible insertion/de-insertion mechanism during charge/discharge process.Our work demonstrates that 3D interconnected NH₄Fe_0.6V_2.4O_7.4@C nanocomposite material could be considered as a potential cathode for sodium ion batteries.General synthesis of ultralong NH₄V₃O₈ nanobelts are investigated as a cathode for sodium batteries for the first time.When used as cathode material for sodium ion batteries,the NH₄V₃O₈ nanobelts with one-dimensional structure show high discharge capacity(211 mAh g^-1 at 50 mA g^-1),nice cycling stability(50 mA h g^-1 is retained after120 cycles under 800 mA g^-1)and good rate capability(166,133,104,and 82 mA g^-1 at100,200,400 and 800 mA g^-1,respectively).The good electrochemical property of the NH₄V₃O₈ is attributed to its unique ultralong nanobelts structure with good structural stability.The results of ex-situ EIS indicate that the NH₄V₃O₈ nanobelts possesses good electrical conductivity and structural stability.Our work demonstrates that t he NH₄V₃O₈nanobelts material could be considered as a potential cathode for sodium ion batteries.Using the hydrothermal-solid phase two-step method,we first prepared the Rb⁺intercalated Na_1.25V₃O₈ one-dimensional material,which was used as the positive electrode material of zinc ion battery,and explored the morphology,structure and electrochemical properties of Rb⁺intercalation.Influence and reveal its mechanism of influence.It is found that Rb⁺intercalation enhances the Odell ripening effect of Na_1.25V₃O₈ one-dimensional material in hydrothermal process,which makes Na_1.25V₃O₈ transform from one-dimensional nanorod to one-dimensional nanobelt,which reduces the specific surface area and inhibits zinc ion.The shuttle also shows that the electrochemical performance of the Na_1.25V₃O₈one-dimensional material after Rb+intercalation is degraded.