Synthesis And Energy Storage Application Of Titanium Dioxide-based Self-supporting Electrode

Lithium-ion batteries have outstanding advantages such as high working voltage,long cycle stability,large energy density,small self-discharge,and no memory effect,so they are involved in almost every field of electronics,especially mobile consumer electronics.The negative electrode,as an important part of the lithium-ion battery,directly determines the performance of the lithium-ion battery.The traditional lithium ion battery negative electrode has a complicated preparation process for a long time.The active material only accounts for 60-90%of the electrode,and the binder hinders the lithium ion diffusion channel,thereby affecting the electrochemical performance.Titanium dioxide?TiO₂?is cheap,stable,safe,and has a small volume change in the process of insertion and extraction of lithium ions.It is considered to be an additive-free anode material with great development prospects.Therefore,the purpose of this thesis is to grow porous TiO₂ coatings in situ on titanium foils,which can be directly used as negative electrodes of lithium ion batteries,moreover modify the surface of them to shorten the ion diffusion path,increase the reaction sites,and then improve lithium storage performance.First,through the micro-arc oxidation reaction,an ultra-thin porous TiO₂ coating is grown in situ on the titanium foil.The rich pore structure facilitates the diffusion of the electrolyte and accelerates the diffusion of lithium ions to the electrode surface.Furthermore,a porous hierarchical structure is formed by composite carbon-based conductive materials,accompanied by nano-sheets growing vertically on the surface,which shortens the ion transport path and reduces the electrochemical impedance greatly.The capacity of lithium storage has been increased by 3 times,reaching 600 mAh cm^-3.After 1,000 cycles,the Coulomb efficiency remains above 98%.It was found that through reduction treatment,oxygen vacancies were introduced into the TiO₂ lattice,which improved electronic conductivity and improved electrochemical performance.Based on this,this paper uses hydrazine hydrate as a reducing agent,to reduces TiO₂ by hydrothermal reaction.The XPS and ESR analysis proved the existence of oxygen vacancies.Nano-particles grow on the surface of the prepared TiO_2-x coating,accompanied by fuzzing surface.With the progress of the charge-discharge reaction,the nanoparticles have no cracks and shedding,and the size gradually becomes smaller and uniform,providing a basis for their excellent cycle performance.Electrochemical tests show that the Rct of the TiO_2-x coating is reduced by an order of magnitude.The first cycle capacity is as high as 840 mAh cm^-3,and the cycle performance is excellent.The capacity of 520 mAh cm^-3 can be maintained after 900 cycles.In order to improve its rate performance,this thesis converts TiO₂ to lithium titanate?LTO?.At the same time,in order to improve its conductivity,a carbon source is introduced in the hydrothermal process and annealed at high temperature to achieve phase transformation and carbonization in one step.Compared with TiO₂ coating,the charge-discharge performance under large current has been significantly improved.This paper proposes a lithium-ion battery anode that is easy to synthesize,high efficiency,superior performance,good stability,environmental protection,low cost,and self-supporting with the development prospects.