Preparation And Modification Of Micron Porous Nb₂O₅ By Solid State Method

The transition metal oxide Nb₂O₅ is considered to be the most promising anode material for the new generation of 2 V lithium-ion batteries due to its cycling stability,high specific capacity,structural stability and safety.However,the transition metal oxide Nb₂O₅ electrode material due to its own low conductivity and poor rate performance and other limitations has been largely limited the further application of the anode material.At the same time,because the current preparation method of Nb₂O₅ is mainly hydrothermal method,such complex preparation method is also difficult to meet the requirements of commercial production.In this paper,the transition metal oxide Nb₂O₅ is the research object.The main purpose is to solve the poor conductivity and poor rate performance of Nb₂O₅ and complex preparation methods.We prepared the transition metal oxide Nb₂O₅ electrode material by solid state method and sintered it.Using institutional exploration and subsequent carbon coating and ionic copper ion doping modification,supplemented by rich characterization methods,we systematically studied the influence of sintering system,coating and doping modification on the structure and morphology of materials with the mechanism of action.The main research contents are as follows:Micron-sized NbSe₂ synthesized by solid state reaction was used as the precursor and the transition metal oxide Nb₂O₅ electrode materials were studied through different calcination temperatures and calcination time.Firstly,NbSe₂ was calcined at 400°C,500°C,600°C,and 700°C for 2 h.XRD and SEM results show that the Nb₂O₅obtained at the calcination temperature below 600°C was the pseudo-hexagonal structure,the Nb₂O₅ calcined at 700°C was orthorhombic structure.All the samples have good microporous hexagonal morphology.The results of electrochemical tests show that the sample calcined at 600°C for 2 h exhibits the best electrochemical performance.The charge capacity of the sample at the current density of 0.2 C for the first time reach 178 mAh g^-1,and at the current density of 1 C after 200 cycles,the charge capacity of 158 mAh g^-1 is still maintained,with the capacity retention rate of95%.In addition,the high ratio of pseudo-capacitor current response makes the sample exhibit good rate performance,and its charge capacity is still 86 mAh g^-1 at a current density of 20 C.The EIS results also show that the sample has the lowest charge transferresistance.Then,the calcination experiments of NbSe₂ were carried out at 600°C for different time?2 h,4 h,6 h,8 h?.XRD and SEM results show that the increase of the calcination time at the same calcination temperature will not affect the crystal structure of Nb₂O₅,but with the increase of the calcination time,the morphology of the sample is gradually broken,with the electrochemical performance gradual decay.Nb₂O₅ calcined at 600°C for 2 h was carbon-coated with glucose,polydopamine and PAN as different carbon sources,and the coating amount was 12wt%.XRD results show that the original crystal structure of the material does not change after carbon coated with different carbon sources.SEM results show that the integrity and dispersion of the particles coated with glucose remain good.Electrochemical test results show that Nb₂O₅ coated with glucose exhibits the best electrochemical performance.Subsequently,glucose was used as a carbon source for different coating amounts,and the coating amounts were 6wt%,9wt%,12wt%and 15wt%,respectively.XPS and TEM results show that 12wt%glucose coated Nb₂O₅ has the best crystal structure,regular microporous hexagonal morphology,showing good rate performance and long cycling stability.The charge capacity of the sample at the current density of 0.2 C for the first time is 228 mAh g^-1 and its capacity retention rate is 100%after 50 cycles.The high rate of pseudocapacitor capacitance current response makes the capacity of the sample also maintains at 110 mAh g^-1 even at the current density of 20 C.Nb₂O₅ calcined at 600°C for 2 h was doped with Cu²⁺,and the doping amounts were 0.05,0.075 and 0.01,respectively.XRD results show that the Cu doping does not change the original crystal structure of the sample.SEM and TEM results show that the Cu doping will have a certain effect on the morphology of the material.The morphology of the sample with a doping amount of 0.075 can basically maintain the original porous hexagonal sheet shape.Electrochemical test results show that different Cu doping have a greater impact on the modification effect of Nb₂O₅.When the Cu doping amount is0.075,the Cu_0.075Nb_1.97O₅ maintains a reversible capacity of 219 mAh g^-1 after 50 cycles at a current density of 0.2 C.Even at a high current density of 20 C,it has a capacity of up to 124 mAh g^-1.