Preparation And Lithium Storage Properties Of Nanostructure T-Nb₂O₅ Composite

The rapid development of electric vehicles has put forward higher requirements for the high power density and high energy density lithium ion batteries.Recently,T-Nb₂O₅ becomes an attractive Li ion intercalation host for power batteries owing to its ultra-fast Li ion transport kinetics.However,the poor electronic conductivity of T-Nb₂O₅(3×10^–66 S cm^–1)resulting from a large band gap of 3.4 e V limits the release of its high rate capability.To circumvent this issue,two composites of porous T-Nb₂O₅/C nanospheres and T-Nb₂O₅@Mo O₂ nanorods were synthesized to release the ultrahigh rate capacibility of T-Nb₂O₅.Our work mainly includes the following two parts:?1?We report a solvethermal method to synthesize mesoporous Nb?IV?-doped T-Nb₂O₅/C nanospheres formed by the agglomeration of Nb₂O₅ nanocrystals and conductive carbon.The electronic conductivity of Nb₂O₅ nanospheres has been significantly improved to 1.469×10^–2S cm^–1through Nb?IV?doping and carbon compositing.Compared with the T-Nb₂O₅ without Nb?IV?and carbon,the T-Nb₂O₅/C exhibits extraordinary rate performance and good cycling stability.Furthermore,the hierarchical structure of T-Nb₂O₅/C material affords a high compact density of 2.34 g cm^–33 when used it as Li ion battery electrodes.The good conductivity and high compact density enable T-Nb₂O₅/C electrode to deliver a higher capacity of 85.4 mAh g^–1after100 cycles at 5 C at a high mass loading of 4 mg cm^–2,compared with the 56.3 mAh g^–1for commercial T-Nb₂O₅.The electrochemical measurement results indicate that the T-Nb₂O₅/C nanospheres not only own improved electronic conductivity and fast ion transport kinetics benefiting from the nanostructure,but also show a practical compact density like a block material,which is favourable for achieving high volume.?2?A homogeneous T-Nb₂O₅ nanorod array was in-situ fabricated on the Nb foils by hydrothermal method,one-dimensional structure of T-Nb₂O₅ nanorods can significantly shorten the transport path of lithium ions and electron.In order to further improve the conductivity of T-Nb₂O₅,core-shell T-Nb₂O₅@Mo O₂ nanorod array was successfully prepared by impregnation and heat-treatment under reducing atmosphere.The T-Nb₂O₅@MoO₂ exhibits better rate performance and cycle stability after coating with a highly conductive Mo O₂ film on the surface of T-Nb₂O₅ nanorods.T-Nb₂O₅@Mo O₂ delivers a high capacity of 42.4 m Ah g^–1after 130 cycles at a current density of 2 A g^–1,accompanied with a capacity retention rate of 87.8%.While the capacity retention rate of T-Nb₂O₅ is only 32.8%with obvious capacity fading.Electrochemical impedance spectroscopy test shows that T-Nb₂O₅@Mo O₂ has a smaller charge-transfer resistance compared with T-Nb₂O₅.Furthermore,the Li⁺diffusion coefficient of T-Nb₂O₅@Mo O₂ is as high as 4.93×10^–1818 cm² s^–1.It proves that the T-Nb₂O₅@Mo O₂ material has faster lithium ion transport kinetics than T-Nb₂O₅.