Controllable Preparation And Electrochemical Properties Of Tungsten Oxide Based Anode Materials

With the consumption of traditional energy sources and environmental pollution,development of renewable energy is urgent.Among renewable energy,lithium ion batteries have attracted attention as a continuous energy supply device.However,the rise of electric vehicles,hybrid vehicles and large-scale energy storage equipment has made traditional lithium-ion batteries unable to meet people's needs.Therefore,the development of lithium ion batteries with higher energy density and higher cycle stability has become an urgent goal.Compared with traditional graphite-type anode materials,tungsten oxide has attracted close attention due to its abundant reserves,high intrinsic density,rich framwork diversity and high theoretical capacity.But the tungsten oxide-based anode material also has some disadvantages,such as poor conductivity,large volume change during charge and discharge and so on.Thence,the electrochemical stability of tungsten oxide is improved by nanocrystallization,heat treatment and surface coating technology.The main research contents and results are as follows:(1)The WO2.8 nanowires were prepared by solvothermal method.By controlling the synthesis conditions,the nanowires with uniform morphology,length of 0.7-1.2 ?m and diameter of 0.01-0.02 ?m can be prepared.Electrochemical tests are as follows: it has an initial discharge specific capacity of 655 m Ah g-1 at a current density of 200 m A g-1 and a discharge specific capacity of 335 m Ah g-1 after 100 cycles,capacity remains stable during the 3-100 cycle cycle.(2)The effects of heat treatment were investigated.The WO2.8 nanowires were used as raw materials to investigate the different heat treatment conditions,including heat treatment temperature and holding time.A series of WO3 materials with different morphologies and structural features were obtained.It is mainly based on the removal of PVP on the surface of WO3 nanowires,and further surface fusion growth to form a layered flower-like morphology and a monoclinic crystal structure.Electrochemical tests are as follows: layered flower-like WO3 has an initial discharge specific capacity of 1129 m Ah g-1 at a current density of 200 m A g-1 and a discharge specific capacity of 760 m Ah g-1 after 100 cycles.(3)The effect of surface coating was investigated.The surface of WO2.8 nanowire was coated with dopamine by solution method,and the WO3@C composite was obtained by calcination and carbonization.The results show that the prepared composites have a uniform core-shell structure,and core-shell materials can be obtained with adjustable cavity,nitrogen doping and composite component(WO2.83 and WC)by carbonization at 500 °C,700 °C and 900 °C.Electrochemical tests are as follows: WO3@C 500 material has an initial discharge specific capacity of 925 m Ah g-1 at a current density of 200 m A g-1 and a discharge specific capacity of 370 m Ah g-1 after 100 cycles.In summary,the preparation of nano-tungsten oxide by one-step solvothermal method and two modification methods of heat treatment and surface coating have improved the electrochemical performance of tungsten oxide to some extent and provided a reference for the coating of nano-tungsten oxide.