Multifunctionalization Of Titanium Dioxide And Its Pseudocapacitive Sodium Storage Behavior

New energy storage technology is a major issue that needs to be solved urgently for human society under the guidance of the"carbon neutral carbon peak"policy.In the past 30 years,lithium-ion batteries have been widely used in various electronic components,new energy power vehicles and other fields on account of their low self-discharge,high safety,long cycle life,environmental friendliness merits,which bring significant benefits to modern society.However,due to the shortage of lithium resources,sodium of the same main group as lithium has been favored by researchers as a substitute.Sodium is abundant in reserves,low in price,and has a similar"rocking chair"working mechanism as lithium,so the current research on sodium batteries is also"leading the way".However,the redox potential of graphite is low.When it is used as a sodium anode,due to its lower working voltage relative to the deposition voltage of sodium metal,sodium tends to deposit on the surface of graphite,thereby promoting the growth of sodium dendrites.It seriously impairs the battery life,thus resulting in the inability of reversible deintercalation of Na ions in commercial lithium-electric graphite anodes.In this paper,starting from titanium dioxide（TiO₂）,three kinds of composite electrode materials are carefully designed,and their sodium storage mechanism is studied.The specific research contents are as follows:1.Through the reduction reaction with sodium hypophosphite（NaH₂PO₂）,an amorphous layer with many oxygen vacancy defects is introduced on the surface of TiO₂.The existence of defects can reduce the band gap of TiO₂,speed up the ion transport rate and enhance the charge storage performance;at the same time,the host TiO₂ phase ensures the high capacity and stable cyclability of this anode material;in addition,pseudocapacitive charge storage provides additional storage sites for sodium ions,enhances the reaction kinetics,and ensures electrochemical performance at high rates performance.Electrochemical results show that the P-TiO₂ nanoparticles have an ultra-stable cycle life(167 m Ah g^-1 at 20 C after 2000 cycles and a capacity retention of95.9%),which is comparable to that of pure P-TiO₂ nanoparticles without phosphorus doping and oxygen vacancies.Compared with the TiO₂ electrode material,the energy density of the battery has been greatly improved.Subsequently,a P-TiO₂|Na₃V₂（PO₄）₂F₃ full cell was constructed,and the key scientific issues facing the practical application of this anode material were discussed.2.Using metal-organic framework（MIL-125）as the precursor,by coating polydopamine（PDA）,and after high temperature carbonization heat treatment,the porous p-TiO₂@NC material was finally obtained.The product retains the unique circular shape of MIL-125.The cake-shaped,porous and high-surface-area p-TiO₂@NC composites accelerate the reversible deintercalation of Na⁺;the electrochemically active species TiO₂ is coated with nitrogen-doped carbon,and this framework can facilitate interfacial electron transport,resulting in Fast reaction kinetics;at the same time,anatase TiO₂ with a specific（001）crystal face exposed has higher activity,lowers the deintercalation barrier of Na⁺,and further improves the sodium storage properties of the material.Electrochemical results show that p-TiO₂@NC micro-nanodiscs exhibit ultra-stable cycle life(130 m Ah g^-1 at 90 C after 10,000 cycles and a capacity retention of 87.8%).Subsequently,a p-TiO₂@NC|Na₃V₂（PO₄）₃ full cell was constructed,and the key scientific issues facing the practical application of this anode material were discussed.3.Based on the self-sacrificial template method,Co₃[Co（CN）₆]₂ Prussian blue analog（Co-Co PBA）was used as the precursor,and coated with a TiO₂coating on the outside via the sol-gel procedure,followed by high temperature gas phase carbonization and selenium.A nitrogen-doped carbon Co Se₂composite（TNC-Co Se₂）with TiO₂ protection was constructed.The material retains the original cubic morphology,and the nitrogen-doped carbon skeleton can promote interfacial electron transport,thereby promoting the improvement of reaction kinetics;secondly,TiO₂ acts as a protective layer to inhibit the structural collapse of the material during cycling,making it The energy density remains stable;additionally,this hybrid structure facilitates robust pseudocapacitive charge storage,resulting in high-rate cycling stability.Electrochemical results illustrate that the TNC-Co Se₂ microcubes exhibit remarkable ultra-stable cycling ability(464 m Ah g^-1 at 6.4 A g^-1 after 6,000cycles and a capacity retention of 92.7%).Subsequently,a TNC-Co Se₂|Na₃V₂（PO₄）₂F₃ full cell was constructed,and the key scientific issues facing the practical application of this anode material were discussed.