Study On The Preparation And Surface Modification Of Nano-Ti₂Nb₁₀O₂₉ Electrode And Its Lithiation/deliatiation Behavior

Lithium ion batteries(LIB s)have been applied in a wild range of fields including smart grids,electronic vehicles and portable devices owing to their high energy density and cycle stability.The negative material is one of the most critical issues which have substantial influence on the performance of LIBs.However,to meet the growing demands in quick charge and long duration ability of devices,developing high-rate LIB is imperative and the commercial graphite anode could no longer satisfy the requirements of the high-rate LIB.Titanium niobate(Ti2Nb10O29,TNO)which is regarded as a suitable anode candidate for high-power LIBs,has excellent structural,high capacity and endurance of fast/over charge and discharge owning to its Wadsley-Roth shear structure.Unfortunately,its low electrical conductivity and Li+diffusion coefficient hamper its high-rate performance.Thus,in this dissertation the aim is improving the reaction kinetics of Ti2Nb10O29 via conductive 3D structure skeleton constructing,nanosizing and surface modification by nitrogen-carbon coating strategies.First,we report carbon nanofibers/TNO core-shell arrays grown on carbon cloth(CNFs@TNO/CC)as anode material to promote lithium-ion diffusion kinetics,enhance the capability property,and ameliorate the rate performance and cycling stability.Such architecture as LIB anode has several obvious advantages.(1)The unique core-shell structure of nanosized TNO particles uniformly anchored on CNF surface improves the lithium-ion transfer efficiency.(2)The CNF arrays with an optimized length served as a bridge increase the conductivity of TNO nanoparticles,and also as a strong support enhance the mechanical stability of composite arrays.(3)Most important of all,compared to the conventional linear arrays,the intertwined and interconnected CNFs@TNO arrays can form a tridimensional conductive network,which is conductive to fully boosting their LIB performance.Consequently,CNFs@TNO/CC exhibits a high reversible capacity of 182 mAh g-1 at an ultra-large current rate of 80 C,and impressive cycle stability(192 mAh g-1 after 1000 cycles at 10C).Then the porous Ti2Nb10O29 hierarchical nanospheres coated with thin nitrogen-doped carbon were prepared using a facile in-situ thermal annealing method.ZIF-8 membrane uniformly coated outside of the as-prepared Ti2Nb10O29 microspheres is used as carbon and nitrogen source to obtain a thin coating layer of nitrogen-doped carbon(NPC).It is found that the NPC derived from ZIF-8 in-situ thermal annealing improves the as-prepared TNO by constructing a three-dimensional conductive network skeleton that facilitates electron transmission and limiting the TNO secondary grains to a nano-size.Thus,significantly reducing the diffusion distance of lithium ions and accelerated mass transfer process.The TNO@NPC porous microspheres possess a unique hierarchical structure and excellent high-rate performance(226 mAh g-1 at 1OC).Futhermore,the solid-state full cell assembled with lithium iron phosphate(LFP)are tested to illustrate its practical application.The full cell TNO@NPC//LFP exhibits 212 mAh g-1 at 5C and retains 187 mAh g-1 after 1000 cycles at 10C,showing well cycle stability.