The Preparation Of Molybdenum-niobium Based Oxide Composites And The Investigation Of Their Lithium Storage Properties

With the rapid development of economy,electrochemical energy storage systems are playing an increasingly important role in consumer electronics,electric vehicles,hybrid electric vehicles,aerospace and smart grids.Lithium-ion batteries are popular among consumers because of their large capacity,high operating voltage,small size and light weight.As one of the important components of lithium-ion battery,anode material is the key point of developing new and high efficiency lithium-ion battery,which has aroused the interest of many researchers.At present,the most widely used graphite anode materials have gradually failed to meet the high standard of human production and life.Molybdenum niobium oxide is one of the most studied anode materials in recent years.It stands out from other materials by virtue of its high theoretical capacity and safe operating voltage window.Improving the conductivity of electrode materials and the migration rate of lithium ions in the process of operation,and keeping the structure stablity of the battery in the process of charge and discharge are the key to fabricate higher capacity and safer lithium-ion batteries.In this work,the mixed phase of Mo₁₃O₃₃/Nb₂O₅metal oxides was synthesized,and a propery comparison was made with pure Nb₂O₅synthesized under the same reaction conditions.The larger size of Mo atom can affect the crystal structure to a certain extent and provide a wider and more favorable channel for lithium-ion transport.Abundant active sites and twisted lattices at the two-phase interface can improve the reaction kinetics,thus improving the conductivity and energy storage capacity.In addition,Mo₁₃O₃₃contains intrinsic oxygen vacancies,which can improve the overall electrical conductivity of the material.The excellent performance of Mo₁₃O₃₃/Nb₂O₅microspheres is due to the synergistic effect of the interconnected microstructures and the improvement of the electrical conductivity of Mo₁₃O₃₃.After 1000 cycles at 500 m A g^-1,the specific capacity of Mo₁₃O₃₃/Nb₂O₅remains at 136.66 m A h g^-1,while Nb₂O₅is only 71.96 m A h g^-1.Then,an ultra-thin flake-like MoNb₁₂O₃₃（F-MNO）nanosheet was successfully synthesized by a solvothermal method and a high temperature calcination through adjusting the concentration.The unique porous nanosheet structure can enhance the contact area between electrode and electrolyte,which is more beneficial to shorten the ion transport distance than other MNO structures.In addition,we also coated the MNO particles with a thin carbon layer（F-MNO@C）to improve their overall electrical conductivity.Another advantage of this experiment is that the thickness of the carbon layer can be controlled by changing the reaction time of chemical vapor deposition.The carbon layer can connect the MNO particles to each other into a complete conductive network and act as a scaffold in electrochemical behavior to maintain structural stability during the cycling testing process.The initial coulomb efficiency of F-MNO@C is 96.29%.Remarkably,the capacity of F-MNO@C is remained at 144.23 m A h g^-1after 1000 cycles,which is much higher than that of F-MNO at 88.75 m A h g^-1,showing excellent electrochemical performance.