Preparation And Lithium Storage Performance Of Titanium Dioxide Nanocomposites

The increasingly severe environmental problems caused by the widespread use of fossil energy have motivated the rapid development of lithium-ion batteries with high energy density and environmental sustainability,and developing high-performance electrodes for lithium-ion batteries has gained great research effort in recent years.TiO₂is one of the most attractive choices due to its low cost,environmental friendliness,high safety,and good stability.However,the low conductivity and theoretical specific capacity of TiO₂limit its practical application.Based on the good stability of TiO₂,we constructed three kinds of nanostructured TiO₂ composites,considering elaborate design of the composition and structure in this thesis.Various material measurements are used to systematically investigate the physical and chemical performance,preparation process and improved lithium storage performance of the TiO₂ composites.Firstly,the modification of V₂O₅ nanosheet cathode with TiO₂ as the structural auxiliary component was studied.A facile and controllable liquid-phase self-assemble strategy was proposed to uniformly decorate V₂O₅ nanosheets with TiO₂ and Ag nanoparticles simultaneously,resulting in novel Ag-TiO₂/V₂O₅ composites.The influence of solvent on the self-assembly process was explored,and the poor solvent THF for V₂O₅nanosheets is the key to the success of self-assembly.It should be stressed that our strategy boasts precise control over the loading density of the nanoparticles on the nanosheets.The introduction of Ag improves the conductivity,and TiO₂ nanoparticles can effectively isolate the V₂O₅ nanosheets from restacking,shorten the Li⁺diffusion pathway,and increase the contact area between electrode and electrolyte,thus providing more electrochemically active sites.Consequently,the resulting Ag-TiO₂/V₂O₅ composites exhibit improved lithium storage performance over neat V₂O₅ nanosheets.A high reversible capacity of 266 mAh g^-1 is achieved at a current density of 100 mA g^-1 after100 cycles.Based on the good cycling stability of TiO₂ anode,hierarchical CNT@TiO₂@Mn₃O₄nanostructures composed of 2D TiO₂ nanosheets,1D carbon nanotubes and 0D Mn₃O₄nanoparticles were constructed by combining solvothermal with above mentioned self-assembly method.In this composite,each component plays a unique,indispensable role.2D TiO₂ nanosheets being flexible in nature are able to inhibit the aggregation of the Mn₃O₄ nanoparticles as well as buffer their volume variation suffered during the charging/discharging process.1D CNTs serve not only as a backbone to improve conductivity,but also maintain material structural stability.0D Mn₃O₄ nanoparticles contribute an extraordinarily high theoretical capacity and are capable of physically isolating the TiO₂ nanosheets,which is favorable for the contact of active materials and electrolyte.The resulting CNT@TiO₂@Mn₃O₄ composites exhibit enhanced cycle and rate performances,delivering a reversible capacity as high as 516 mAh g^-1 at 500 mA g^-1after 300 cycles,and 251 mAh g^-1at 2000 mA g^-1 after 600 cycles.Considering the enhancement in lithium storage performance of the hierarchically assembled composites,Fe₃O₄ nanoparticles were assembled on TiO₂ nanosheets to prepare TiO₂@Fe₃O₄,which were mixed with CNTs and then filtered to prepare TiO₂@Fe₃O₄/CNT composite films.Highly conductive CNTs are cross-linked with each other to form three-dimensional porous conductive network for fast electron transport,and effectively disperse TiO₂@Fe₃O₄,avoiding their agglomeration as well as preserving the advantages of two-dimensional structure.Fe₃O₄ nanoparticles uniformly distributed on the surface of TiO₂ nanosheets,provide high capacity and isolate the nanosheets from restacking.TiO₂ nanosheets with good flexibility not only alleviate the large volume change of Fe₃O₄ upon cycling,but also limit the agglomeration of the nanoparticles.The composite films were wet-transferred onto copper foil and directly used as binder-free anodes for lithium-ion batteries,showing improved rate performance.After 1000 cycles at 5000 mA g^-1,a reversible specific capacity of 225 mAh g^-1 could be remained.