Design,Synthesis And Electrochemical Performance Of Core-sheath Micro-/Nanostructured Transition Metal Compound Electrode Materials

The micro-/nanostructured core-sheath materials can make maximum use of the interface area between the nanostructures and strengthen the interaction between the inner core and the outer shell layer.Moreover,the coating layer can stabilize the structure of the inner core and prevent the aggregation of particles so that more active sites are exposed.These features could bring special and novel properties to the material,changing the intrinsic characteristics of the original micro-nanostructured material.Therefore,researchers can further tune their electrical,mechanical,catalytical and other properties by structural design and size control of the core-sheath structures.So far,the core-sheath structured micro/nano-materials have been widely used in the field of electrochemical energy storage.In this thesis,we have synthesized three kinds of transition metal electrode materials with a core-sheath structure by using atomic layer deposition including NiCoP@FeP_x nanowire arrays,Mn₃O₄@ZnO nanosheet arrays and ZnMn₂O₄/C@TiO₂ nanofibers.Besides,the electrocatalytic hydrogen evolution reaction?HER?and zinc-ion srorage properties of the products are investigated.The main contents and results are listed as belows:?1?Nickel-cobalt oxide nanowire arrays coated with iron oxide were uniformly grown on the conductive nickel wire by a hydrothermal process and atomic layer deposition,and then the NiCoP@FeP_x multimetallic phosphide nanowire arrays with a stable core-sheath structure were obtained by phosphorization.The HER performance and reaction kinetics of NiCoP@FeP_x nanowire arrays in acidic and alkaline electrolytes were systematically investigated.The overpotentials of NiCoP@FeP_x are only 82.5 and 96 mV at the current density of 10 mA cm^-2,respectively.Besides,the core-sheath NiCoP@FeP_x nanowires still exhibit excellent electrochemical HER performance after 4000 cycles.?2?The core-shell structured Mn₃O₄@ZnO nanosheet arrays were synthesized on the carbon cloth by a microwave hydrothermal process and atomic layer deposition.We have investigated the effect of ZnO layer on the aqueous Zinc-ion batteries?AZIB?electrochemical performance of Mn₃O₄@ZnO nanosheets systematicially.It is found that the capacity retention of Mn₃O₄@ZnO nanosheets increases from 27.3%to 60.3%compared to Mn₃O₄ nanosheets after 100 cycles at a current density of 100 mA g^-1 and the rate performance has also improved dramatically.These results demonstrate that the introduction of a ZnO coating layer can improve the AZIBs electrochemical performance of materials.?3?The core-sheath structured ZnMn₂O₄/C@TiO₂ nanofibers assembled with nanoparticles have been successfully prepared by electrospinning,atomic layer deposition and subsequent annealing treatment.The electrochemical performance has been studied intensively.The capacity retention of ZnMn₂O₄/C@TiO₂ nanofibers is improved from 66.4%to 96.1%compared with ZnMn₂O₄/C nanofibers after 100 cycles at a current density of 200mA g^-1 and the rate performance has also increased significantly.It is found that the deposition of ultra-thin TiO₂ layer on the surface of ZnMn₂O₄/C nanofibers can improve the cycle stability and rate performance of materials.