Research On Full Battery Application And Asymmetric Capacitor Based On Niobium Oxide Anode Material

With the continuous development of the consumer electronics market and the electric vehicle market,higher requirements have been put forward for the energy density,power density,cycle life and safety of electrochemical energy storage devices.Traditional graphite anode materials have been unable to meet the demand for high power output.Therefore,it is urgent to find a new type of anode material with high specific capacity and high rate performance.Among them,niobium-based oxide can achieve hige rate lithium insertion/extraction due to its unique two-dimensional layered structure,which can realize structural stability and high rate perfoemance.It has been a promising new generation of negative electrode materials.However,the low electronic conductivity has always been the main problem that limits its practical application.This paper mainly focuses on the application of niobium-based oxides in electrochemical energy storage,and carries out researches on the performance of pounch full-cell batteries based on Ti Nb₂O₇anode materials,and the modification and application of Nb₂O₅ as anode materials for hybrid supercapacitors.The main work content and research results are as follows:As the negative electrode material of the full battery,the rod-like structure Ti Nb₂O₇was prepared by high temperature solid state method.The commercial NCM811 was used as the positive electrode material.The best cycle stability and capacity retention rate of the pounch cell were obtained when N/P was 1.05.The discharge specific capacity at 0.3C was 155.3 mAhg^-1,respectively,the capacity retention rate after 100 cycles is 90%,and the capacity retention rate after 200 cycles is 80%,showing the practical application potential of TiNb₂O₇.The microscopic morphology,crystal structure,surface elements and valence of the disassembled positive and negative pole pieces is analysed.It is believed that the main reason for the capacity decline of the TNO||NCM811 pounch full battery comes from the negative electrode material Ti₂Nb₂O₇.The SEI film with LiF and Li CO₃ as the main components is formed on the surface of the negative electrode during the cycle.At the same time,the TNO particles may have micro-area distortion and cracks during the cycle.The crystallinity of the material becomes worse,which increases the resistance of the ion intercalation.The above reasons make the capacity of the whole battery continue to decay.Nb₂O₅ microspheres with a diameter of about 2～4μm were prepared by hydrothermal method.The microspheres were assembled from two-dimensional sheet-like Nb₂O₅,and Nb₂O_5-x with abundant oxygen vacancy defects was obtained by hydrogenation modification.XPS,EPR and other characterizations confirmed the existence of oxygen deficiency.The discharge specific capacity of Nb₂O_5-x/4h after 1000cycles of 0.5Ag^-1 cycle is 157.38mAhg^-1,and the capacity retention rate is 82.8%,showing the best rate performance and cycle stability.Nb₂O_5-x||AC hybrid capacitors have significant capacitance characteristics.,The discharge specific energy and discharge specific capacitance are 185Whkg^-1/188Fg^-1 at 0.5Ag^-1,and the retention rates after1200 cycles are respectively 87.4%/72.8%.This is because the introduction of oxygen vacancy defects can shorten the band gap,increase the surface charge density of the electrode material,and essentially increase the electronic conductivity of the Nb₂O₅material.In addition,part of the Nb⁵⁺is reduced to Nb⁴⁺,result in the enlarged lattice spacing and low the lithium ion diffusion energy barrier.