Nickel-based And Cobalt-based Metal Oxides Nanocomposites: Fabrication And Their Lithium Storage Properties

Due to the high theoretical capacity,enhanced safety and low cost,nickel-based oxides and cobalt-based oxides?eg.Ni O,Co₃O₄ etc?have been regarded as promising candidates as alternative anode materials for Li-ion batteries?LIBs?.However,the lithium storage mechanism of some new anode materials?eg.Ni₃V₂O₈,Co₃V₂O₈?is complicated,that need to be further clarified.In addition,the electrochemical performance of nickel-based oxides and cobalt-based oxides is unsatisfactory because of their low electrical conductivity,large volume variation and subsequently capabilities recession upon a charge-discharge process,which should be further optimized.In this thesis,we developed a series of nanostructured nickel-based oxides and cobalt-based oxides electrodes,to enhance their lithium storage properties.We explored the preparation method and the lithium storage mechanism of these materials,investigate the key factors that affect the electrochemical performance of developed new anode materials.The main contents and results was listed as follows:?1?A simple and morpho-genetic route had been developed for the fabrication of hierarchically nanostructured Ni₃V₂O₈ and its nanocomposites.A hierarchically flower-like Ni₃V₂O₈ superstructure had been successfully synthesized using a facile one-step hydrothermal approach.It was found that the p H value of the mixed precursor solutions played a key role in the formation of flower-like Ni₃V₂O₈ structure.Importantly,the flower-like Ni₃V₂O₈ showed good electrochemical performance as an anode material for LIBs,and delivered 1047.8 m Ah g-1 at 200 m A g-1 after 300 cycles.Furthermore,the lithium storage mechanism of Ni₃V₂O₈ involving in a conversion reaction?Ni O to Ni?and an intercalation reaction?Lix V2O5 to Lix+y V2O5?was proposed by ex-situ XRD analyses.On this basis,we fabricated the novel hierarchically flower-like Ni₃V₂O₈/Co₃V₂O₈ nanocomposites for the first time.The flower-like Ni₃V₂O₈/Co₃V₂O₈ nanocomposites exhibited superior cycling stability?933.2 m Ah g-1 at 500 m A g-1 after 600 cycles?than flower-like Ni₃V₂O₈.These excellent electrochemical properties may be contributed by the unique 3D hierarchical structure of the Ni₃V₂O₈/Co₃V₂O₈ material,and the synergistic affects between the Ni₃V₂O₈ and Co₃V₂O₈ nanoparticles.?2?A new nanostructure of Mx Oy/M₃V₂O₈?M=Ni?Co?nanocomposites arrays on Ti foil were successfully designed and prepared,and their Li-storage properties were investigated systemly.The Co₃O₄/Co₃V₂O₈ hybrid nanowires were fabricated by a stepwise hydrothermal strategy and subsequent annealing treatment,it delieved a high initial discharge capacity of 1677 m Ah g-1 at 200 m A g-1 and retained at 1251.0 m Ah g-1 after 200 cycles.The excellent electrochemical performance could be attributed to the synergistic effects of the two metal oxides in lithiation-delithiation process.Furthermore,the Ni O/Ni₃V₂O₈ nanosheet arrays on Ti foil were successfully prepared by a one-step hydrothermal strategy and subsequent annealing treatment.It exhibited an enhanced cycling and rate performance compared with single Ni O electrode.Even at a high rate of 8000 m A g-1,a large capacity of 425.0 m Ah g-1 was still reached.Upon altering the current density back to 100 m A g-1,the capacity of was recovered to 898.3 m Ah g-1.The superior electrochemical performance of the Ni O/Ni₃V₂O₈ nanosheet arrays was relevant to a novel electrochemical reconstruction,which results in enhanced reaction kinetics owing to the formation of a new symmetrical porous architecture during the cycling process.?3?The M₃V₂O₈/Ni foam?M=Ni?Co?nanocomposites were synthesized for the first time and their Li-storage mechanism,Li-storage perfoamce and the key factors that affect the electrochemical performance were studied deeply.The Co₃V₂O₈/Ni and Ni₃V₂O₈/Ni nanocomposites were prepared by a simple one-step procedure using a low-temperature and low-cost hydrothermal method.The charge/discharge mechanism of Co₃V₂O₈/Ni and Ni₃V₂O₈/Ni based on conversion and intercalation reaction routes were further verified by ex-situ XRD diffraction and CV.When used as a new sort of binder-free anode for LIBs,the Co₃V₂O₈/Ni and Ni₃V₂O₈/Ni nanocomposites delievered 1289.0 and 1286.8 m Ah g-1 respectively,after 100 cycles at 200 m A g-1.Even when the current was 10000 m A g-1,discharge capacity of 471.4 and 477.7 m Ah g-1 could be achieved.The superior electrochemical performance was attributed to the original structural advantages of the Co₃V₂O₈/Ni and Ni₃V₂O₈/Ni composites.More importantly,unique nanostructure of nanocomposites induced the electrochemical reconstruction during the cycling process,resulted in improved reaction kinetics,electrochemical activity and structure stability,this was an internal factors that affect the electrochemical performance of electrode materials.?4?Stimulated by the advantages of above designed electrodes,we design and fabricate a Co₃O₄/Co₃V₂O₈/Ni foam nanocomposites for the first time,their Li-storage mechanism and Li-storage perfoamce were investigated systemly.Hierarchically nanostructured Co₃O₄/Co₃V₂O₈/Ni nanocomposites were prepared by a two-step hydrothermal synthesis and subsequent annealing treatment.The one-dimensional?1D?Co₃O₄ nanowire arrays directly grew on Ni foam,whereas the 1D Co₃V₂O₈ nanowires adhered to parts of Co₃O₄ nanowires.Most of the hybrid nanowires were inlayed with each other,forming a 3D hybrid nanowires network.Unique Hierarchical nanostructure can provided sufficient electrolyte-electrode contact area and buffered the volume variation caused by the Li-ion insertion/extraction.Meanwhile,unique 3D macroporous structure induced the formation of a new symmetrical porous architecture during the cycling process,which leads to improve electrochemical performance.As a result,the discharge capacity of Co₃O₄/Co₃V₂O₈/Ni nanocomposites could reach 828.1 m Ah g-1 even after 600 cycles at 1000 m A g-1,which demonstrates great potential of Co₃O₄/Co₃V₂O₈/Ni nanocomposites as promising electrode material for LIBs.