Study On The Construction And Energy Storage Performance Of Tungsten-based Nanostructures

In recent years,with the maturity and rapid development of new energy power generation technologies,the development of large-scale,high-energy-density and low-cost energy storage systems has become the primary problem to be solved for the grid application of the scale new energy power.Lithium-sulfur batteries have attracted much attention due to their high energy density,high specific capacity and low cost,in turn have be considered as one of the most promising large-scale high-energy density energy storage systems.Meanwhile,due to the abundant sodium resources,sodium-ion batteries have become an important choice for the development of inexpensive large-scale energy storage systems.However,due to poor conductivity of the sulfur positive electrode,serious volume expansion,and the shuttle effect of the soluble lithium polysulfide during charge and discharge,the battery performance is seriously attenuated.At the same time,since the ionic radius of sodium ions is larger than that of lithium ions,commercial anode materials for lithium ion battery cannot be applied to sodium ion batteries,so finding a suitable anode material is the primary task of developing sodium ion batteries.In order to solve the main problems in front of lithium-sulfur batteries and sodium ion batteries,the design and development of high-performance nanostructure energy storage materials has become one of the important research field.In terms of the abundance of tungsten resources,China possess important advantages on resources and price.Meanwhile metal nitrides and sulfides have good electrical conductivity.Therefore,there are important scientific significance and using value to design and develop nano-structured tungsten-based energy storage materials for lithium-sulfur and sodium ion batteries.Based on the above background,in this dissertation,a series of tungsten nitride and sulfide nanorods,nano-foam blocks and microspheres have been designed prepared through the strategy of hydrothermal chemcial method.The specific research results are as follows:?1?To enhance the utilization of sulfur in lithium-sulfur batteries,three-dimensional tungsten nitride?WN?mesoporous foam blocks are designed to spatially localize the soluble Li₂S₆ and Li₂S₄within the pore spaces.Meanwhile,the chemisorption behaviors of polysulfides and the capability of WN as an effective confiner are systematically investigated through density functional theoretical calculations and experimental studies.The theoretical calculations reveal a decrease chemisorption strength between WN and the soluble polysulfides?Li₂S₈>Li₂S₆>Li₂S₄?,while the interactions between WN and the insoluble Li₂S₂/Li₂S show a high chemisorption strength of ca.3 eV.Validating theoretical insights through electrochemical measurements further manifest that the assembled battery configurations with sulfur cathode confined in the thickest WN blocks deliver the best rate capabilities(1090 and 510 mAh g^-1 at 0.5 C and 5 C,respectively)with the highest initial coulombic efficiency of 90.5%.Moreover,a reversible capacity of 358 mAh g^-1 is maintained with a high coulombic efficiency approaching to 100%,even after 500 cycles at 2 C.As guided by in silico design,this work not only provides an effective strategy to improve the retentivity of polysulfides,but also underpins that properly architectured WN can be effective retainers of polysulfides.?2?In order to develop high performance sodium ion battery anode materials,a series of tungsten sulfides with different morphology and nanostructures such as nanorods,nanoblocks and microspheres were designed and successfully fabricated.Compared with WS₂ nanoblocks and WS₂microspheres,WS₂ nanorods deliver a better sodium ion storage properties due to the larger specific surface area short diffusion distance and better crystallinity.In order to further improve the conductivity of WS₂ while mitigating the large volume change during charge and discharge process,a layer of rGO is coated on the surface of WS₂ nanorods by freeze-drying method to effectively improve the structural stability and rate capability.The electrochemcial testing results indicate that the as-prepared rGO@WS₂ nanorods composites exhibit both good sodium ion and lithium ion storage performace.After cycling for 500 cycles at 500 mA g^-1,its sodium storage capacity is still maintained at 65.9 mAh g^-1.And after cycling for 500 cycles at 1000 mA g^-1,its lithium storage capacity can be maintained at 288.3 mAh g^-1.