Study On The Application Of Zinc Sulfide And Its Nanocomposites In Lithium-ion Batteries And Lithium Sulfur Batteries

With the development of the industrialization,the problem of energy shortage is one of the problems that mankind urgently needs to solve.Lithium-ion secondary batteries have been widely used in the commercial applications due to their high energy density,temperature cycling performance,and non-memory effect.However,the active material of the lithium ion battery is usually coated on a current collector.It is easy to deform during the long-cycle,resulting in the pulverization,even fall-off,of active materials,which further cause the declined cycling performance and safety problems.However,active materials are often deposited directly on the substrate in thin film lithium-ion batteries through magnetron sputtering technology,which has higher density and stronger adhesion.It can effectively avoid the above-mentioned problems.Considering the advantages of zinc sulfide thin film negative electrode,such as nontoxic,low cost,high thermal and chemical stability,and high theoretical specific capacity,etc.,in the first part of the research,the zinc sulfide film negative electrode material which is expected to be used in all solid-state thin-film lithium-ion battery is studied.The preparation methods of zinc sulfide and zinc oxide film are introduced in detail.The morphology and structure are explored through a variety of material characterization technologies,and then half cells are assembled to compare the differences in electrochemical performance.In contrast to ZnO films,ZnS films show less polarization and higher cycle stability,which is owed to the improvement of reversibility of conversion reaction.On the other hand,commercial lithium-ion batteries are getting closer to their theoretical capacity and can hardly meet the requirements of long-distance driving.Lithium-sulfur batteries have attracted the attention of academia and industry due to their high theoretical specific capacity(1672 mAh g-1).However,the development of lithium-sulfur batteries also encountered bottlenecks.For example,the nonconductivity of elemental sulfur,the volume expansion/contraction effect during the reaction,and the shuttle effect of lithium poly sulfide.As a polar transition metal sulfide,zinc sulfide can form polar chemical bonds with lithium polysulfide.The chemical bond is much greater than the intermolecular van der Waals force(the main force between polar molecule and nonpolar molecule).The lithium-sulfur shuttle effect caused by the dissolution of the intermediate product polysulfide is one of the biggest bottlenecks of lithium-sulfur batteries.Therefore,in the second part,the zinc sulfide/graphene composite was synthesized by hydrothermal method,and then used as a carrier for the sulfur cathode to improve its lithium storage performance.Meantime,the calculation of density functional theory(DFT)was used to illustrate the adsorptive and catalysis ability of the composite toward polysulfides.The lithium-sulfur battery pouch cells have verified its practical prospects,showing that metal sulfide composites can effectively decrease the polarization of lithium-sulfur batteries.