Investigation Of Vanadium Niobium Oxide As Anode Material For Lithium-ion Battery

In this work,VNb₉O₂₅ and V₄Nb₁₈O₅₅,which are thermodynamically stable in the V₂O₅-Nb₂O₅ systems,are prepared by electrospinning.As the general synthetic temperature of the materials in V₂O₅-Nb₂O₅ system is higher than 1000 ^oC,the synthetic temperature that is nearly half as low as that of the original method in electrostatic spinning method is a great improvement for the preparation of these materials.The rod like VNb₉O₂₅ is similar with the good crystalline VNb₉O₂₅ obtained from the traditional preparation method,which can provide the initial reversible capacity of 205.03 mAh g^-1at the current density of 100 mA g^-1,and can maintain a capacity retention of 94.22%after 200cycles.The initial reversible capacity of the pored ribbon VNb₉O₂₅ material is the higher 220.38mAh g^-1,which reaches the theoretical capacity of VNb₉O₂₅ in the voltage range in the test.After200 cycles,the pored ribbon VNb₉O₂₅ can maintain a capacity retention of 95.16%.Moreover,even after 500 cycles under the current density of 1000 mA g^-1,the pored ribbon VNb₉O₂₅ sample can still maintain the reversible capacity of 132.3 mAh g^-1 with the retention rate of 92.97%.In-situ XRD test is used to study the mechanism of lithium ions intercalation/deintercalation in VNb9O25.It was observed that not only the reduction of Nb⁵⁺to Nb⁴⁺occurred in the electrochemical reaction process,but also the reduction of Nb⁴⁺to Nb³⁺,which can explain the reason for the cavity in VNb9O25 crystal structure holds excess lithium ions.According to the theoretical calculation,the theoretical capacity of V₄Nb₁₈O₅₅ in the voltage range of 1-3 V?versus Li/Li⁺?is 271.83 mAh g^-1.The best prepared sample can provide the specific capacity of 251.56 mAh g^-1 at the current density of 100 mA g^-1,which can reach 92.54%of the theoretical capacity.The reversible capacity of the material in diacharge/charge process is236.04 mAh g^-1,which still achieves 86.83%of theoretical capacity with the capacity loss of only10.16%.This indicates that V₄Nb₁₈O₅₅ has a great potential for electrode material.Besides,V₄Nb₁₈O₅₅ can maintain the reversible capacity of 157.73 mAh g^-1 after 1000 cycles at the rate of1200 mA g^-1.By investigating the lithium ions intercalation/deintercalation mechanism of V₄Nb₁₈O₅₅,it can be found that lithium ions transport rapidly in three directions in the crystal structure of materials.It can explain why materials have excellent rate performance.