Study On The Controllable Preparation Of Titanium-based Oxide Anode Materials And The Performance Of Their Lithium-ion Capacitors

With the increasing demand for energy and the environmental pollution caused by the combustion of fossil energy,it is urgent to develop high performance electrochemical energy storage systems.Lithium ion capacitors have become a hot research,because of its high power density and high energy density.The key factor affecting the performance of lithium ion capacitors is the kinetic gap between the two electrodes caused by their different energy storage mechanisms.In order to narrow the kinetic gap,it is very important to develop novel anode materials with improved reaction dynamics.Among the anode materials,titanium-based oxides have attracted much attention,due to their good cycling stability,excellent rate performance,high safety and low cost.However,their low intrinsic conductivity and poor lithium ion diffusion limit their further applications.The aim of this thesis is to improve the electrochemical performance of titanium-based oxides by morphological control,oxygen vacancy modification and recombination with reduced graphene oxide.The main research contents are as follows:?1?FeTi₂O₅ material with special morphology was prepared through the combination of electrospinning and heat treatment.The relationship between structure and performance is analyzed by morphological structure characterization and electrochemical performance test.The results show that the smaller size of primary particle could increase the lithium ion diffusion by shortening the ion transport distance;the nano-chain structure is beneficial to the directional transport of electrons and ions,enhancing the conductivity and ion transport performance;the 3D network-like structure connected by nano-chains is not only beneficial to electron conduction,but also avoids the capacity attenuation caused by agglomeration.Therefore,when evaluated as anode,FeTi₂O₅ exihibits excellent electrochemical performance.Furthermore,the LIC was designed and assembled by using FeTi₂O₅ as anode and superconductive carbon black?SCCB?as cathode,which can deliver a high energy density of 112 Wh kg^-1 and a power density of 67500 W kg^-1.?2?TiNb₂O_7-x material was prepared through the combination of electrospinning and heat treatment,and the existence of oxygen vacancies was proved by HRTEM and XPS characterizations.The electrochemical tests indicated that the presence of oxygen vacancies can not only improve the conductivity,but also provide more active sites for lithium ion storage.In addition,the chain-like structure of electrode materials is beneficial to the directional transport of electrons and ions,which can enhance the conductivity and ion transport performance.Compared with other titanium niobate materials without oxygen vacancies,TiNb₂O_7-x exhibits superior rate performance,higher specific capacity.The as-fabricated TiNb₂O_7-x nanochains also has a good cycling stability with 91.5%discharge capacity retention over 2000 cycles at the current density of 1.0 A g^-1.The TiNb₂O_7-x//SCCB can deliver a high energy density of 114 Wh kg^-1 and a power density of 22502.4 W kg^-1.?3?Roselle-like Zn₂Ti₃O₈ nanomaterials was firstly prepared by a simple hydrothermal method.Then,the Zn₂Ti₃O₈/rGO nanocomposites were achieved by freeze-drying and thermal reduction treatment.Their morphology and structure were analyzed by SEM,TEM and XPS characterization methods.The results demonstrated that a compact interface was formed between Zn₂Ti₃O₈ and rGO,which would facilitate the electron transfer to enhance the reaction kinetics.Furthermore,the relationship between structure and performance was further explored by electrochemical tests and calculations.By comparing the electrochemical properties of Zn₂Ti₃O₈ and Zn₂Ti₃O₈/rGO,it was found that the introduction of rGO can not only provide more space for lithium storage by increasing the specific surface area,but also avoid the agglomeration of electrode materials by forming a 3D electron conduction network.The LIC was designed and assembled by using ZTO/rGO nanocomposite as anode and superconductive carbon black powders?SCCB?as cathode.Remarkably,the as-fabricated LIC device can deliver a high energy density of 204 Wh kg^-11 at a power density of 112.5 W kg^-1 and remain 55 Wh kg^-1 at an ultrahigh power density of 67500 W kg^-1,which is superior to other similar LICs.