Preparation And Research On Storage Lithium Performance Of Niobium-based Metal Oxide

The development of high-performance anode materials is of great significance to further improve the energy density,power density,and cycle performance of lithium-ion batteries.Niobium-based oxide and Li₄Ti₅O₁₂ have the same lithium storage mechanism,high lithium intercalation potential（1～2V）,large rate charge and discharge,and excellent cycle performance.At the same time,compared with Li₄Ti₅O₁₂,the niobium-based oxide has a higher specific capacity due to its polyvalent states.Therefore,niobium-based oxides are expected to become new anode materials for lithium-ion batteries.However,the inherent low conductivity of niobium-based oxides has limited development,and modifications are needed to improve electrochemical performance.Therefore,in this paper,hollow NiNb₂O₆,flake SnNb₂O₆ and one-dimensional CuNb₂O₆ nanowire materials were synthesized,which were carbon composite modified and the performance of lithium-ion half-cells and lithium-ion capacitors were investigated:The surface of the hollow NiNb₂O₆ particles was coated by dopamine self-polymerization reaction,and NiNb₂O₆ materials coated with nitrogen doped carbon（NiNb₂O₆@NC）were obtained by calcination,and the effects of different dopamine coating amounts on their lithium storage performance were investigated.The results showed that the morphology of the coated NiNb₂O₆ particles did not change,and the thickness of the coated carbon layer increased with the increase of the amount of dopamine.When the mass fraction of dopamine hydrochloride was 20%（relative to NiNb₂O₆）,the prepared NiNb₂O₆@NC-2 had the best lithium storage performance.At 500 m A·g^-1 current density,its specific capacity was325.5 m Ah·g^-1,when the current density was increased to 2000 m A·g^-1,its specific capacity could be maintained at 227.2 m Ah·g^-1.After 500 cycles,its specific capacity retention rate was 94.1%,while the specific capacity retention rate of NiNb₂O₆ sample was only 80.1%.Ex-situ XRD and XPS were used to study the lithium storage mechanism of NiNb₂O₆materials,and the results showed that NiNb₂O₆ materials were mainly lithium-storaged by insertion/extraction type and conversion type.Finally,NiNb₂O₆@NC-2 and AC were used to assemble a lithium-ion capacitor.The device showed a maximum energy density of 123.9Wh·kg^-1 and a maximum power density of 10,000 W·kg^-1 in the voltage range of 0～4.0V.After 5000 times of at 1A·g^-1,the capacity retention rate could still be maintained at 86.1%and the coulomb efficiency was close to 100%.Flaky SnNb₂O₆ was prepared by solvothermal method,which was compounded with graphene oxide in different proportions to obtain SnNb₂O₆@rGOgel samples.Electrochemical tests showed that SnNb₂O₆-100mg@rGO had excellent lithium storage performance.At a current density of 100 m A·g^-1,its specific capacity was 1431.8 m Ah·g^-1.After 100 cycles,its specific capacity remains 544.6 m Ah·g^-1 reversible specific capacity,while SnNb₂O₆ had only162.4 m Ah·g^-1.At a current density of 500 m A·g^-1,after 1000 cycles,the specific capacity of SnNb₂O₆-100mg@rGO could be stabilized at 780 m Ah·g^-1,and the coulomb efficiency was close to 100%.The EIS test was used to study the kinetic characteristics of the SnNb₂O₆-100mg@rGO.The EIS test was used to study the kinetic characteristics of SnNb₂O₆-100mg@rGO.Compared with SnNb₂O₆,it had the smallest charge transfer resistance before and after cycling,indicating that the material hadgood conductivity and accelerated charge transfer rate due to the compounding of graphene.Ex-situ XRD and TEM were used to analyze the lithium storage mechanism and structural changes of SnNb₂O₆,which indicated that SnNb₂O₆ was mainly alloyed and inserted/extracted to store lithiums.One-dimensional CuNb₂O₆nanowires were successfully prepared by electrostatic spinning technology,and the nanowires were loaded on the surface of graphene by electrostatic action.According to electrochemical characterizations such as CV and galvanostatic charge-discharge,CuNb₂O₆/rGO had good electrochemical performance.Among them,CuNb₂O₆/rGO showed a stable reversible specific capacity of 312.2 m Ah·g^-1 at a current density of 100 m A·g^-1,while CuNb₂O₆ was only 175.5 m Ah·g^-1.Meanwhile,CuNb₂O₆/rGO had 183.6 m Ah·g-1 after 2000 cycles at 1000 m A·g^-1,and the coulomb efficiency was close to 100%;CuNb₂O₆/rGO had good electrochemical performance.Among them,CuNb₂O₆/rGO showed a lithium storage capacity of 312.2 m Ah·g^-1 at a current density of 100 m A·g^-1,while CuNb₂O₆ had only 175.5 m Ah·g^-1.At the same time,CuNb₂O₆/rGO had a stable specific capacity of 183.6 m Ah·g^-1 after 2000 cycles at 1000 m A·g^-1,and the coulomb efficiency was close to 100%,CuNb₂O₆/rGO/Li battery had the smallest charge transfer resistance before and after cycling by EIS test,which showed that it had good dynamic characteristics.In addition,the addition of graphene also increased the ratio of plutonium capacitors during lithium ion deintercalation.At the same time,CuNb₂O₆/rGO and AC were assembled into CuNb₂O₆/rGO//AC lithium ion capacitors,which were tested at 0.01～3.8 V.This device exhibited a high energy density of 92.1 Wh·kg^-1 and a high power density of 9475W·kg^-1.Even after 10,000 cycles at a current density of 2 A·g^-1,the device’s capacity retention rate could be maintained at 82.3%,and the coulomb effect was close to 100%.