Facile Preparation And Doping Complex Modification Of TiNb₂O₇ And Ti₂Nb₂O₉

Nowadays,lithium-ion batteries are widely used in many fields such as portable equipment,digital equipment,and communication,because of their high single cell voltage,large specific energy,and safe and reliable cycle stability.With the continuous expansion of the electric vehicle market,graphite anode lithium-ion batteries are currently unable to meet the requirements of high capacity and high power.Having a theoretical specific capacity of 387.5 mAh·g^-11 and excellent cycle stability and safety,TiNb2O7?TNO?has been considered as one of the most promising anode materials for lithium-ion batteries.In this thesis,the preparation and modification of titanium niobate anode materials are mainly studied.Firstly,the optimal conditions for preparing TiNb2O7 by high temperature solid-state method,sol-gel method and solvothermal method were discussed.The optimal conditions of the high-temperature solid-state methods for preparing TiNb2O7materials were:using Nb₂O₅ and TiO₂ as raw materials,and calcining at 1200^oCfor 10 h.The optimal conditions of the sol-gel method were:using KOH as the alkali source,and melting the sample at 800^oC for 2h.The optimal conditions of the solvothermal method were:using NbCl₅ and TBT as raw materials at pH=9 at 200^oC for 12h,with a subsequent calcination of the dried product at 800^oC for 2h.SEM results showed that the TiNb2O7 material obtained by the solvothermal method was microspheres composed of nanoparticles,while the TiNb2O7 material obtained by the high-temperature solid-state method and the sol-gel method had a larger particle size and no loose,porous structure.The half-cell for galvanostatic charge-discharge performance tests revealed that the solvothermally prepared TiNb2O7 material had the best reversible capacity of294.88 mAh·g^-11 at a rate of 0.1C.Secondly,corn cob was used as the raw material to prepare biochar.S and?NH₄?₆Mo₇O₂₄·4H₂O were used as raw materials to prepare MoS₂ with a hollow tubular structure.Then the biochar,TiNb2O7 and MoS2 were sequentially complexed by a solvothermal method,and biochar/TNO/MoS2 composite was successfully obtained.The XRD and SEM results showed that TiNb₂O₇ material was composited on biochar,and MoS2 material was composited on the outermost layer.The galvanostatic charge-discharge performance results showed that the reversible capacity of the composite decreased with the increase of biochar content;while the reversible capacity of the composite increased with the increase of MoS2 content.The discharge capacity of the 5%biochar/TNO/10%MoS₂ composite can reach about 475.1 mAh·g^-1at the rate of 0.1C.Finally,the experimental conditions of preparing Ti2Nb2O9 by high temperature solid-state method were studied,and the optimal condition was calcined at 1200^oC,for10h.A series of Ti₂Nb_2-xV_xO₉ materials with different doping amounts of V⁵⁺were prepared under these conditions.XRD results showed that V⁵⁺ions successfully entered the lattice of the host.The assembled half-cell was subjected to galvanostatic charge and discharge and electrochemical impedance tests.The results showed that the Ti2Nb2O9material could reach a reversible capacity of about 150 mAh·g^-11 at a rate of 0.1C.After4C charging and discharging,the capacity was still maintained 142.5 mAh·g^-1at 0.1C rate The doping of a proper amount of vanadium ions can increase the conductivity of Ti2Nb2O9 materials,but it has no effect on increasing the reversible capacity.