Preparation And Characterization Of M-Nb-O (M=K, Ba)Materials As Energy Storage Materials

High-performance lithium-ion batteries are important for developing sustainable energy.Therefore,the new high-performance anode materials are widely concerned and studied.Recently,Nb-based materials have been considered as one of the most promising anode materials for lithium-ion batteries because of their relatively high specific capacity and excellent cycling performance.Among them,TiNb₂O₇ is the most studied,and it has also been tried to be used in commercial electrodes.However,the poor rate performance of TiNb₂O₇ has not been well solved.Therefore,we explore new materials of K₂Nb₈O₂₁1 and BaNb_3.6O₁₀.In this work,we will focus on the comparison of synthesis methods and electrochemical properties between K₂Nb₈O₂₁microtubes and nanotubes,and the research on electrochemical properties and Li⁺intercalation/deintercalation mechanism of BaNb_3.6O₁₀0 nanowires.Firstly,K₂Nb₈O₂₁1 microtubes of outer diameter?²?m?and wall thickness?⁵00 nm?were synthesized by electrospinning in this work.Additionally,K₂Nb₈O₂₁1 nanotubes of outer diameter?¹60 nm?and wall thickness?⁴0 nm?were synthesized by changing synthesis condition of the flow rate,voltage and calcination temperature.Compared with microtubes,K₂Nb₈O₂₁1 nanotubes exhibit excellent electrochemical properties.K₂Nb₈O₂₁1 nanotubes showed the specific capacity of335 mAh g^-11 at 100 mA g^-11 with capacity retention rate of 87.6%after 500 cycles,a specific capacity of 213 mAh g^-1at 1000 mA g^-1with capacity retention rate 80.3%after 5000 cycles,and a high Li⁺diffusion coefficient in CV,EIS and GITT measurements,respectively.The excellent performance of K₂Nb₈O₂₁1 nanotubes was attributed to the short Li⁺diffusion path.The outstanding structure and electrochemical reversibility were proved by in-situ XRD and ex-situ XPS.Secondly,we also report the preparation of BaNb_3.6O₁₀0 nanowires by electrospinning method.Its cycling performance at different loads,full cell performance with the cathode material of LiMn₂O₄ and Li⁺intercalation/deintercalation mechanism were further studied.BaNb_3.6O₁₀nanowires exhibited a specific capacity of 263.8 mAh g^-11 at a load of 1.5 mg cm^-22 and 100 mA g^-1.Moreover,the capacity retention of 5000 cycles still was 60%at 1000 mA g^-1.Similar reversible capacities were also shown at loads ranging from 1.5 mg cm^-2to 7.5 mg cm^-2.Finally,the cyclic stability and high electrochemical reversibility of BaNb_3.6O₁₀0 nanowires were obtained by in-situ XRD,in-situ TEM and theoretical calculation.Furthermore,the charge/discharge process of Li⁺intercalation/deintercalation can be divided into three stages,which are two solid-solution processes and one two-phase coexistence process.