The Synthesis Of Zinc Sulfide/Carbon Nanocomposite For Lithium/Sodium Storage

With the rapid development of modern society and the increasing depletion of global fossil energy,we urgently need to develop advanced energy conversion and storage technologies.Among them,lithium-ion batteries(LIBs)are regarded as a promising energy storage device due to their advantages such as high energy density and long cycle life,and have broad development prospects.In addition,due to the abundant natural resources and low cost of sodium,sodium-ion batteries(SIBs)have great potential for large-scale energy storage applications.However,with the rapid development of portable electronic devices and electric vehicles,traditional graphite anodes(372 m Ah/g)have been unable to meet the demand for high-power and high-energy-density LIBs.On the other hand,since the ionic radius of Na~+(0.97?)is 55%larger than that of Li~+,the limited interlayer spacing of graphite makes it inapplicable to SIBs.Therefore,exploring a low-cost,high-capacity and well-structured anode material is crucial for the further development of LIBs and SIBs.Among the available alternatives to graphite anode materials,metal sulfides have high theoretical specific capacity and the weaker M-S bond energy further ensures their good reversibility of the reaction,which has attracted extensive attention of researchers.Among them,zinc sulfide(ZnS)stands out among many sulfides due to its advantages of low cost,non-toxicity,and non-polluting.However,the practical application of ZnS anode materials still faces some problems.For example,based on the reaction mechanism of transformation and alloying machine,ZnS will have a huge volume change during the cycle,which will lead to the destruction of the structure of the electrode material and reduce its cycle stability.Meanwhile,the poor electronic conductivity also seriously hinders the Li/Na storage performance of ZnS.In order to solve the above problems,in this work,carbon coating and carbon confinement are used to suppress the volume expansion effect of ZnS and improve the electrical conductivity of the material.Besides,the effect of heteroatom doping on the electrochemical properties of ZnS anode materials was also discussed.The main research contents are as follows:(1)First,hollow carbon spheres(HC)were prepared and sulfonated in concentrated sulfuric acid,and sulfonic groups were introduced on the surface of the HC to induce the growth of ZnS nanoparticles.Secondly,zinc acetate and thioacetamide were used as zinc and sulfur sources,and ZnS nanoparticles were prepared by a simple hydrothermal reaction and loaded on the surface of hollow carbon spheres.Finally,a thin layer of polydopamine(PDA)was coated on the surface of the material and carbonized at high temperature to obtain hollow sandwich structured ZnS/C composite(HSZC).This unique double-carbon shell structure not only facilitates fast ion/electron transport,but also prevents the agglomeration of ZnS during cycling and alleviates its volume expansion.Finally,HSZC exhibits excellent Li/Na storage properties.(2)In order to further improve the performance of the electrode material,selenium powder was used as the selenium source,and it was loaded into hollow carbon spheres by melting method.The subsequent preparation process was the same as(1).Finally,a gradient selenium-doped ZnS/C composite(Se-HSZC)with hollow sandwich structure was obtained.Electrochemical performance tests and DFT calculations show that Se doping can improve the structural stability of the composites and enhance the charge transfer kinetics,thereby significantly improving the electrochemical performance of the electrode materials.Se-HSZC,as an anode material for LIBs,still maintains a specific capacity of 567 m Ah/g after 1500 cycles at a high current density of 4 A/g.When as an anode material for NIBs,Se-HSZC can exhibit a high reversible capacity of 343.5 m Ah/g after 200 cycles at 0.2 A/g.(3)ZnS/carbon fibers composite(ZnS/CFs)were synthesized by electrospinning technology to confine ZnS in 3D interconnected flexible carbon nanofibers.On the one hand,the 3D interconnected carbon network can greatly reduce the electron/ion transport distance to improve the electrical conductivity.On the other hand,carbon fiber can effectively suppress the volume expansion effect of ZnS and improve the structural stability of the electrode material because of the strong physical confinement effect on ZnS.Consequently,the ZnS/CFs anode exhibits excellent cycling stability in SIBs.