Preparation Of Nickel-cobalt Oxide/Nitride And Carbon Nanotubes Composites For The Applications Of Lithium-based Batteries

With the rapid development of electronic portable devices and electrical vehicles,energy storage systems have attracted extensive attention.Lithium-based batteries(such as lithium-ion battery,lithium-sulfur battery,lithium-O₂ battery and so on)have emerged as promising next-generation energy storagy systems due to their high energy density and environmental friendliness.In the development of these batteries,electrode materials paly a crucial role in determining the performance and practical applications.Therefore,it is of great significance to design and synthesize excellent electrode materials.In this thesis,transition metal oxide and carbon nanotubes nanocomposite(Ni Co₂O₄@CNTs),and transition metal oxide-nitride heterostructures composited with CNTs(Ni Co O₂-Ni₃N@CNTs)are proposed.The above materials are applied as the electrodes in the lithium-ion battery and lithium-sulfur battery,respectively.1.Synthesis of Ni,Co-binary metal oxides@carbon nanotubes(Ni Co₂O₄@CNTs)composite electrode and the application as an anode material for lithium ion batteries.Herein,a Ni Co₂O₄@carbon nanotubes(CNTs)composite electrode with advanced architecture is developed through a facile surfactant-assisted synthetic strategy.The introduced polyvinyl pyrrolidone(PVP)can greatly facilitate the heterogeneous nucleation and growth of Ni Co precursor on CNTs and thus benefit the uniform transformation to well-confined Ni Co₂O₄@CNTs composite.The CNTs combined with Ni Co₂O₄ tightly act both as a conductive network for enhancing the ion/electron transfer and as a support for mitigating the volume expansion of Ni Co₂O₄.As a result,the Ni Co₂O₄@CNTs electrode exhibits a high initial capacity of 830.3 m A h g^-1 and good cycling stability of 608.1 m A h g^-1 after 300 cycles at 2000 m A g^-1.2.Synthesis of Ni/Co oxide-nitride heterojunction@CNTs(Ni Co O₂-Ni₃N@CNTs)and the application as a cathode material for lithium-sulfur batteries.Here we report a Ni Co O₂–Ni₃N@CNTs heterostructures that combine the merits of Ni Co O₂with high adsorption to lithium polysulfides(Li PSs)and Ni₃N with high electrical conductivity and catalytic activity to the conversion of Li PSs,thus achieving smooth trapping/diffusion/conversion of Li PSs across the interface.The polar surface of Ni Co O₂ has high adsorption to Li PSs,while Ni₃N promotes the conversion of Li PSs into insoluble Li₂S.The fast diffusion of Li PSs from Ni Co O₂ to Ni₃N helps achieve both high trapping efficiency and fast conversion.As a result,the structure can effectively suppress the shuttle effect and consequently increase the utilization of active materials and improve the cycle stability.The lithium-sulfur battery with Ni Co O₂–Ni₃N@CNTs electrode displayed a high initial discharge specific capacity of 1215.3m Ah g^-1 at the current density of 0.1 C.