Synthesis, Modification And Electrochemical Performance Of TiO₂(B) Nanostructures For Lithium Storage

As energy storage and conversion device,lithium-ion batteries have been widely used in real life.With the popularity of electric vehicles,people's requirements for lithium-ion batteries'performance are increasing day by day.Therefore,it is necessary to develop lithium-ion batteries with a faster-charging speed,longer service life,and more stability and safety.The key to restricting the performance of lithium-ion batteries lies in the electrode materials.As lithium-ion batteries'anode material,TiO₂(B)has a high de-lithium-embedded potential,which can avoid the decomposition of electrolyte and the precipitation of lithium dendrite.Moreover,TiO₂(B)'s volume expansion rate in the de-lithium-embedded process is only 4%,so it has good safety and structural stability.Besides,TiO₂(B)has pseudocapacitance effect,making it have excellent application prospects in rapid charge and discharge.Due to its safety,low volume expansion rate and pseudocapacitance effect,TiO₂(B)have received extensive attention and research.However,its commercial application is impeded by its poor electrical conductivity and lattice stress in lithium removal and intercalation.In this paper,TiO₂(B)nanoparticles,TiO₂(B)nanobelts and TiO₂(B)nanoflowers were synthesized and optimized to improve the electrochemical performance of TiO₂(B)as electrode material for lithium-ion batteries.The main research contents are as follows:(1)TiO₂(B)nanoparticles were prepared by using Ti powder,NH₄OH,H₂O₂,C₂H₄O₃and H₂SO₄as raw materials,and then PEDOT:PSS was coated on the surface of TiO₂(B)nanoparticles by wet coating technology to form TiO₂(B)@PEDOT:PSS composites.Electrochemical test results show that the electrode material coated with PEDOT:PSS has a higher specific capacity and better rate performance.The results of AC impedance spectroscopy showed that compared with the uncoated TiO₂(B)nanoparticles,PEDOT:PSS coating on the surface of TiO₂(B)nanoparticles could effectively reduce the internal resistance and charge transfer resistance of the battery.Kinetic calculation results show that PEDOT:PSS coating can improve the diffusion coefficient of lithium ions.(2)Bulk anatase titanium dioxide was prepared by sol-gel method with tetra-butyl titanate,glacial acetic acid and ethanol as raw materials.The purchased titanium dioxide(P25)and our self-made block anatase titanium dioxide were added into 10 mol/L Na OH solution for reaction,and the corresponding TiO₂(B)nanobelts were obtained.The material characterization results show that the width of TiO₂(B)nanobelt prepared with self-made anatase as the precursor is 50-150 nm,which is narrower than the width of TiO₂(B)nanobelt prepared with P25 precursor(100-250 nm).The results of CV curves at different scanning velocities show that TiO₂(B)stores lithium in the form of pseudocapacitance,while anatase stores lithium in ion diffusion.The calculation results of pseudocapacitance show that the proportion of pseudocapacitance increases with the increase of scanning rate,indicating that lithium is mainly stored by pseudo capacitance at a high magnification rate.The charge-discharge test and rate test results show that the TiO₂(B)nanobelt prepared by the sol-gel method has a better rate and higher specific capacity.The TiO₂(B)nanobelt prepared by the sol-gel method is charged and discharged at 1 C,and the capacity retention rate of the TiO₂(B)nanobelt is 99.1%after 350 cycles..(3)TiO₂(B)nanoflowers were prepared from Ti Cl₃and ethylene glycol,and then GO was prepared from graphite powder,K₂S₂O₈,P₂O₅,concentrated sulfuric acid,H₂O₂and HCl.TiO₂(B)nanoflower graphene hydrogels were prepared by mixing them evenly with GO and using L-ascorbic acid as a reducing agent.After freeze-drying,TiO₂(B)nanoflower graphene aerogel composites were obtained.The results of FESEM showed that the TiO₂(B)nanoflowers were uniformly distributed in the three-dimensional network structure formed by the graphene aerogel,which effectively reduced the agglomeration of the TiO₂(B)nanoflowers.The specific surface area test results showed that the TiO₂(B)nanoflowers aerogel composites had a larger specific surface area than the TiO₂(B)nanoflowers.The electrochemical test results showed that TiO_2()Bnanoflower-graphene-aerogel composites'specific capacity decreased from 196.8m Ah/g to 154 m Ah/g after 1000 charge-discharge cycles at 5 C,and the capacity retention rate was 78.2%.At 10C for 1000 cycles,the battery capacity decreases from 165.6 m Ah/g to133.9 m Ah/g,and the capacity retention rate is 80.8%,showing good rate performance and cycle stability.