Preparation Of Metal Cation Doped V₂O₅ Microspheres And Their Application In Lithium-Sulfur Batteries

With the rapidly development of human society,classical lithium-ion batteries have been difficult to fill the market demand for high-energy energy storage devices.With a higher theoretical capacity and energy density,lithium-sulfur（Li-S）batteries have great advantages including cheap and environment-friendly,show a very promising application.However,the slow redox kinetics of sulfur,and the dissolution and shuttle effect due to lithium polysulfides（Li PSs）,as well as bad performance during practical applications with a higher sulfur loading and poor electrolyte adding,seriously hampered the development of Li-S batteries.In this paper,a series of electrocatalytic materials with unique structures have been designed and synthesized according to the metal cation doping strategy to address the deficiencies of Li-S batteries,which are applied to the efficient catalytic host of sulfur.The main studies are as follows:1.The doped V₂O₅materials were synthesized by hydrothermal method by Fe,Co and Ni atoms with the same period and atomic size in combination with the V atom.The results show that the Fe,Co or Ni doped V₂O₅materials（M-V₂O₅-YS）,similar to the undoped V₂O₅,are microspheres with a special yolk structure with a diameter of about 1.5μm.The introduction of cations not only effectively improves the electrical conductivity of V₂O₅,but also,enriches the active sites of V₂O₅for enhanced chemical anchoring of Li PSs.Meanwhile,the unique yolk structure can raise the loading of sulfur.Consequently,the composite anode exhibits favorable electrochemical performance.Especially for the S/Co-V₂O₅-YS cathode,can still stabilize an excellent reversible discharge capacity of 693.7 m Ah g^-1at such a high current density of 5 C.2.W⁶⁺and Mo⁶⁺ions with larger than V atoms and higher positive charge than V⁵⁺were selected to dope the V₂O₅microspheres.The doping of ions with larger charge numbers causes lattice distortion of V₂O₅and generates oxygen vacancy defects.Such defects would not only improve the chemisorption ability of V₂O₅to Li PSs,and also promote their interconversion.The electrochemical results show that the W-doped V₂O₅composite cathode,in particular,yields more remarkable rates and cycle performance.In particular,the S/W-V₂O₅cell can still realize good sulfur utilization even under high sulfur loading(5.5 mg cm^-2)and low electrolyte addition(6μL mg^-1).3.La and Ce,the rare earth elements,with larger radius but less charge number than V⁵⁺were selected for doping of V₂O₅microspheres.La and Ce ions,with special electronic structure,doped V₂O₅microspheres,have an abundance of active sites.Even at a beginning rate of 0.3 C,the initial capacities for 1227.1 m Ah g^-1and1065.6 m Ah g^-1were obtained from S@YS-Ce-V₂O₅and S@YS-La-V₂O₅cathodes,respectively.When the current density was increased to 5 C,the reversible capacity of S@YS-Ce-V₂O₅525.4 m Ah g^-1.At the same time,has a superior cycling stability as well as a higher electrochemical conversion efficiency.The kinetic test results highlight that the La and Ce doped V₂O₅materials can dramatically expedite the liquid-solid conversion kinetics in Li-S batteries.In conclusion,this work systematically studies the application of different metal cation doped-V₂O₅materials as the sulfur hosts in Li-S batteries,reveals their chemisorption effect on Li PSs,and further clarifies the catalytic mechanism between the doped-V₂O₅materials and sulfur.The strategies and results of this paper are conductive to broaden the application of transition metal oxides in Li-S batteries,which has certain reference significance for the development of high-performance key materials.