Preparation And Performance Of Tungsten-Based Heterostructure Materials For Lithium-Sulfur Batteries

Lithium-sulfur batteries are deemed to be one of the most promising energy storage systems due to their high theoretical energy density and the natural abundance,green,and clean sulfur resources.However,problems such as the shuttle effect of polysulfides and slow kinetics during the conversion reaction,resulting in rapid battery capacity decay and low utilization of active materials,which pose a significant obstacle to the actual process of lithium-sulfur batteries.In response to the above problems,this thesis takes tungsten-based materials as the research object,and rationally designs them through defect engineering and construction of heterostructure strategies to improve the adsorption and catalytic capabilities for polysulfides.The primary investigations in this thesis are as follows:WO_2.83/CC with oxygen vacancies are designed and fabricated as interlayer materials for lithium-sulfur batteries.The experimental results indicate that WO_2.83/CC has a stronger affinity for sulfur species and can effectively anchor polysulfides.The battery exhibits an outstanding specific capacity of 973.82 m Ah g^-1at current density of 1 C,with an average decay rate of 0.074%per cycle after 400charge-discharge cycles.Even at a high current density of 2 C,it can still cycle stably for 700 cycles,maintain a high discharge specific capacity of 467.25 m Ah g^-1,and the coulombic efficiency is basically maintained at 100%.The improved performance is due to the fact that the oxygen vacancies in WO_2.83 facilitate the acquisition of a stronger adsorption effect on polysulfides,the shuttle effect of lithium-sulfur battery is alleviated.And WO_2.83/CC after reduction treatment retains the nanoarrays structure of precursor,which facilitates the rapid transport of lithium ions.To further improve the electrochemical properties of WO_2.83/CC interlayer,WO_2.83-WN/CC heterostructure is prepared by high temperature nitriding treatment.The experimental results indicate that the WO_2.83-WN/CC heterostructure can effectively reduce the nucleation barrier of Li₂S,which can enhance the reaction kinetics of polysulfides.The battery exhibits a high initial discharge specific capacity of 1509.37 m Ah g^-1 at a current density of 0.1 C,and an average capacity decay rate of only 0.034%per cycle after 1500 stable cycles at a current density of 2 C.Even at a high sulfur loading of 3.47 mg cm^-2,it exhibits a high discharge specific capacity,and 68.86%of the capacity can be maintained after 90 stable cycles.The improved performance can be attributed to the synergistic effect of strong chemical anchoring ability of WO_2.83 and high catalytic activity of WN,which improves the adsorption-catalytic conversion performance of polysulfides.In addition,the carbon cloth substrate and nanoarrays structure facilitate the physical confinement of polysulfides and provide a fast charge transfer channel,inhibit the dissolution and diffusion of polysulfides.