Preparation And Electrochemical Performance Of TiO₂?B? And Iron-based Oxides As Anode Materials For Lithium-ion Batteries

With the development of portable electronic products,new energy vehicles and grid battery systems,the rapidly incremental demand for energy has driven the development of electrode materials of lithium-ion batteries?LIBs?to go beyond conventional graphite anodes and attain higher energy density and lower cost.TiO₂?B?has a highest theoretical capacity to store charge?335 mAhg-1?compared with the rutile and anatase.Due to a relatively larger channel structure,TiO₂?B?is particularly suitable for the lithium-ion diffusion.Three major obstacles that have prevented the wide adoption as an anode material for lithium-ion batteries,one being the low diffusion rate of lithium-ion,In addition,the low intrinsic electrical conductivity,the last one being the using of conductive agents and additives,which reduce the energy density.Iron-based oxides,including ferroferric oxide?Fe₃O₄?and hematite??-Fe₂O₃?are the most promising anode materials because of its advantages,including high theoretical capacity of 924 mAhg-1 and 1007 mAhg-1,respectively,environment friendly,natural abundance.However,the practical application of iron-based oxides as anodes of LIBs faces a significant challenge of the notoriously fast capacity degradation upon cycling.The poor cycle stability originates from the intrinsically large volume change and aggregation of hematite particles along the lithiation/delithiation process.in this paper,according to the different characteristics of TiO₂?B?,Fe₃O₄ and ?-Fe₂O₃,we proposed to synthesize 3D TiO₂ by using pure titanium,and the specific surface area of TiO₂ was increased and the capacity of TiO₂ was improved;3DOM Fe₃O₄ was obtained by electrodeposition of Fe₃O₄ on PMMA template,and the structure of 3DOM was used to alleviate the stress during the charge and discharge process;The 3DOM TiO₂/CoPt/?-Fe₂O₃?3DOMTCF?composites wereprepared by the combination of 3DOM TiO₂ and CoPt and ?-Fe₂O₃,and the cycling stability of ?-Fe₂O₃ was improved.In chapter 3,3D TiO₂?B?were synthesized directly on Ti foil substrate as a three-dimensional anode for lithium ion batteries.3D TiO₂?B?exhibits promising electrochemical performance,the discharge capacity is extremely high capacity of396.2 mAhg-1 at a current density of C/20,though it decays gradually,it is still high as 124.9 mAhg-1at a current density of 2C.The dramatic improvement in reversible capacity is ascribed to the unique structure of 3D nanowire array,which provides good electronic conductivity and accessible lithium ion paths,and do not use any conductive agents and additives.In chapter 4,the 3DOM Fe₃O₄ as the anode material is prepared by electrodepositing on the copper current collector covered with PMMA template,which is removed by annealing subsequently.It was found that the 3DOM Fe₃O₄ showed excellent electrochemical performance,it delivers a stable capacity of 633 mAhg-1 for up to 100 cycles at density of 250 mAg-1.In chapter 5,a three-dimensional ordered macroporous TiO₂/CoPt/?-Fe₂O₃?3DOMTCF?nanocomposite was synthesized via a sol-gel approach templated by poly methyl methacrylate?PMMA?microspheres.After magnetized,3DOMTCF anode exhibited extremely high reversible capacity of 540 mAhg-1with the current density of 50 m Ag-1 and long cycle life with more than 84% capacity remained after250 cycles?current density of 200 mAg-1?.Results from post-analysis indicated that the excellent electrochemical behaviors of magnetized were ascribed to the unique structure of 3DOMTCF,which provide sufficient space for large volume change and a internally established magnetic field for keeping pulverized active materials.