Preparation Of Tungsten Oxide Composites And Its Application In New Energy Devices

The development of industrialization and globalization has greatly promoted the demand for environmentally friendly and efficient energy in countries around the world.Lithium ion battery has become the mainstream of energy storage equipment for its advantages of high power density,flexible structure,high efficiency and good environmental performance.Nowadays,the theoretical specific capacity of mainstream anode graphite is very low(372 m Ah/g)and the rate performance is poor.It is very necessary to find alternative anode materials with high specific capacity and long cycle life.As a transition metal oxide,tungsten oxide(WO₃)has a theoretical capacity of 693m Ah/g and a large lattice spacing(3.7(?)).However,WO₃ has defects such as large volume change,prone to agglomeration and poor electrical conductivity during the process of lithium intercalation/delithiation,which severely limits its commercial development.Therefore,this paper designed the embedded WO₃@N-CNF composite,and explored its electrochemical properties and lithium storage mechanism.The main research work and innovations of this paper are as follows:(1)The double one-dimensional embedded WO₃@N-CNF composite was successfully prepared by the combination of hydrothermal and electrospinning and two-step annealing process,and the growth mechanism and morphology of the material were systematically explored.The increased O content through the conversion of WO_x to WO₃ provides more reactive sites for the lithiation reaction.N-CNF can not only wrap ultrafine WO₃nanowires,effectively prevent the direct contact of WO₃ with the electrolyte,reduce secondary reactions and prevent nanowire agglomeration,but also effectively limit the volume expansion of WO₃.The uniformly distributed N doping greatly improves the conductivity,and the double one-dimensional structure can also provide more Li⁺diffusion channels,shorten the diffusion path of lithium ions,and accelerate the diffusion of Li⁺.(2)Compared with WO_x and N-CNF,WO₃@N-CNF exhibits excellent rate capability and stable cycling performance,which is attributed to the double one-dimensional embedded structure and excellent surface pseudocapacitive effect.The fast reaction kinetics of the surface pseudocapacitance-dominated mechanism leads to the rapid diffusion of lithium ions,which contributes to the improvement of electrochemical performance.At 1.0 mV/s,the surface pseudocapacitance contribution of WO₃@N-CNF is as high as 91.71%.At 0.2 A/g,the initial specific capacity is 838.5m Ah/g,which rises to an astonishing 950 m Ah/g after 300 cycles,showing superior reversibility and stability.However,the cycling performance of WO₃@N-CNF is still unsatisfactory at high current density.(3)At high current density,compared with the composite electrodes with different contents of WO₃,WO₃@N-CNF-3 has the best coulombic efficiency and cycle performance.The cycle performance of the composite electrode was improved by comparing samples with different contents of WO₃.A small amount of WO₃ has little improvement in capacity and will destroy the integrity of N-CNF;excessive WO₃ cannot form a hermetic embedded structure,and at the same time,the severe volume expansion will lead to the collapse of the lattice structure of WO₃ and the destruction of the N-CNF structure,which further leads to battery damage.WO₃@N-CNF-3 can effectively balance the ratio between WO₃ and N-CNF,showing the best performance.