Synthesis And Energy Storage Properties Of Ti-Based Oxides As Anode Materials For Lithium-Ion Batteries

As an important clean energy source,Lithium-ion batteries are widely used in various fields,such as aerospace,electronic products and electric vehicles.With the rapid development of science,technology and economy,Lithium-ion batteries have been unable to meet the growing energy needs of people.Anode materials are one of the important factors affecting the development of Lithium-ion batteries.As a common transition metal oxide,titanium dioxide has been used as anode material for Lithium-ion batteries due to its advantages of low cost,environmental protection and stable physical and chemical properties.However,its poor electronic and ionic conductivity limits its application.Researchers all over the world usually design it into nano-scale or composite with conductive materials to prepare titanium-based oxide composites with outstanding properties.In this paper,the surface of C@TiO₂ nanocomposites was prepared by solvothermal method and calcination at high temperature;CNTs-C@titanium dioxi TiO₂ composites were prepared by self-assembled deposition of titanium dioxide on the basis of conductive network of CNTs and pyrolytic carbon layer;and C@TiO₂/3D pollen carbon composites were prepared by controlling the hydrolysis of TBT with hollow pollen carbon spheres as skeleton and glucose as carbon coating.The main research contents and results are as follows:1.In this paper,C@TiO₂ nanocomposites were successfully prepared by solvothermal method and high temperature calcination.Under the catalysis of KCl,the esterification of acetic acid with ethylene glycol yields esters and water molecules.Water molecule promotes hydrolysis of tetrabutyl titanate,and water molecule consumption promotes esterification,which is similar to self-catalyzed reaction.The precursor was calcined at high temperature in N₂ atmosphere to obtain C@TiO₂nanocomposites.A series of characterization methods and electrochemical tests were used to study the structure,morphology and electrochemical properties of the composites.The results show that,compared with pure titanium dioxide,C@TiO₂nanocomposites exhibit not only stable structure but also excellent electrochemical properties during charge-discharge cycle.The first charge-discharge capacity of C@TiO₂ composites is 757/374 mAh g^-1,corresponding to the first Coulomb efficiency of 49.4%.Even at the current density of 1.6 A g^-1,the capacity can be maintained at 176.5 mAh g^-1.2.CNTs-C@TiO₂ composites were successfully prepared by solvothermal method with CNTs as additive.Deionized water promoted the hydrolysis of tetrabutyl titanate to obtain Ti（OH）₄ particles,which were deposited on the surface of CNTs.Polyethylene glycol was synthesized by the polymerization of ethylene glycol under the action of Ti⁴⁺,and CNTs-C@TiO₂ composite was obtained by calcination at high temperature.Under the synergistic action of pyrolytic carbon and CNTs,the conductivity and structural stability of the composites have been greatly improved.Therefore,CNTs-C@TiO₂ composites have excellent electrochemical properties as negative electrode materials for Lithium/Sodium-ion batteries.3.C@TiO₂/3D pollen carbon composites were successfully prepared by solvothermal method and high temperature calcination,using hollow pollen carbon spheres as skeleton and glucose as carbon coating.The structure,morphology and crystalline phases of the material were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,Raman spectroscopy（Raman）and specific surface area test（BET）.After a series of electrochemical tests,it was confirmed that C@TiO₂/3D pollen carbon composites had excellent electrochemical properties.The results show that the first charge-discharge capacity of C@TiO₂/3D pollen carbon composites is 263.1/331mAh g^-1 at 1 C current density,and the corresponding Coulomb efficiency is 79.4%under the action of conductive network composed of pollen carbon spheres and pyrolytic carbon at 700℃.After 100 cycles,the capacity was maintained at 203.1mAh g^-1,and the capacity retention rate was close to 100%.In order to better study the excellent electrochemical properties of the composites,C@TiO₂/3D pollen carbon composites were charged and discharged 1000 times at 5 C.The capacity of the composites could still be maintained at 148 mAh g^-1,and the coulombic efficiency was close to 100%.