Modification And Electrochemical Performance Of Titanium Niobate Anode Material

Secondary lithium-ion batteries have been widely used in the fields of electric vehicles,mobile devices,and grid energy storage.However,with the accelerated pace of social life and the frequent occurrence of battery explosions,the battery market has put forward higher requirements for energy storage devices in terms of fast charging,cycling stability and safety,etc.TiNb₂O₇（TNO）anode material has high theoretical capacity(388m Ah·g^-1),good structural stability,high reversibility,and a working potential of about 1.6 V,effectively avoiding the formation of solid electrolyte interphase（SEI）films and lithium dendrites,thus ensuring high safety.Therefore,TNO is an ideal choice for high-power lithium-ion battery anode.However,the poor electrical conductivity of TNO material limits its commercial application.In order to improve the performance of TNO material,this study focuses on the modification of TNO through methods such as ion doping,optimization of preparation processes,and the introduction of new conductive materials.Modified TNO materials with excellent rate performance were obtained.The main research content and results are summarized as follows:1.M_0.03TNO（M=Mn,Ce,W）materials were prepared by high-temperature solid-state method,and the effects of ion doping on their structural and electrochemical properties were investigated.The results showed that all three types of ion doping increased the unit cell volume,decreased the particle size and improved the electrochemical properties.Among them,the W_0.03Ti_0.97Nb₂O₇ sample exhibited the smallest charge transfer impedance and the largest lithium ion diffusion coefficient with the best charge/discharge performance,and the specific capacity reached126.9 m Ah·g^-1 at 20 C rate,and the specific capacity retention rate was91.26%after 250 cycles at 1 C rate.Further samples of W_xTNO（x=0.01,0.03,0.05,0.1,0.15）were prepared and the influence of W⁶⁺doping on the electrochemical performance was investigated.The results showed that as the W⁶⁺doping amount gradually increased to 0.1,the particle size of the material decreased and transformed into a more plate-like shape.The charge transfer impedance gradually decreased,and the lithium ion diffusion coefficient gradually increased,showing the best rate performance,and the specific capacity reached 152.7 m Ah·g^-1 at 20 C rate,and the capacity retention rate was 94.63%after 250 charge/discharge cycles at 1 C.XPS analysis confirmed that W⁶⁺doping increased the concentration of Ti³⁺and Nb⁴⁺ions in the material,which contributed to the improvement of electronic conductivity.However,when the W⁶⁺doping amount was higher,the samples synthesized by the solid-state method did not achieve a pure phase material matching the TiNb₂O₇standard card,indicating the need for further optimization of the preparation process to improve the electrochemical performance of doped-modified W_xTNO materials.2.The W_xTi_1-xNb₂O₇（x=0.05,0.1,0.15）samples modified with high content of W⁶⁺doping were successfully prepared by the liquid-phase method,which further improved their rate properties.When prepared by the conventional solvothermal method,W⁶⁺doping did not change the crystalline phase of TiNb₂O₇,and pure phase materials were obtained even at x=0.15.To further meet the requirements of practical applications,this study attempted to combine the acid-assisted peroxide method with spray drying to achieve low-temperature crystallization under ambient pressure.The modified materials prepared by this method were all microspheres assembled from primary nanoparticles.With the increase of W⁶⁺doping,the size of primary nanoparticles gradually increased,and the degree of crystallization significantly improved,while the monoclinic crystal structure of TiNb₂O₇ with a sheared Re O₃ structure remained unchanged.The electrochemical performance results showed that the sample with x=0.1 exhibited the best charge/discharge performance,with a charging specific capacity of 266 m Ah·g^-1 at 0.1 C rate.It maintained a high specific capacity of 167.7 m Ah·g^-1 at a 20 C rate,and even after 250charge/discharge cycles at 1 C rate,it still retained a specific capacity of226.5 m Ah·g^-1 with a capacity retention rate of 93.4%.Compared to the solvothermal method,the W_0.1Ti_0.9Nb₂O₇ material prepared using the acid-assisted peroxide method combined with spray drying significantly reduced the charge transfer impedance and exhibited better high-rate performance and cycle stability.3.To enhance the interparticle conductivity of the material,the monolayer MXene（Ti₃C₂）-modified TiNb₂O₇ material was prepared by the solvothermal method,and the calcination conditions were optimized.Subsequently,the proportion of MXene addition was further optimized.The results showed that the composite material exhibited the best electrochemical performance when the MXene addition amount was 5%of the theoretical mass of TiNb₂O₇.It demonstrated high specific capacity(182.7 m Ah·g^-1 at 20 C)and a high capacity retention rate of 95.09%（1 C,250 cycles）.The performance improvement can be attributed to the following three aspects:1)TiNb₂O₇ nanoparticles were uniformly distributed in the layered MXene material,forming a three-dimensional conductive network,which improved the conductivity.2)The nanoparticles were anchored in the layered structure of MXene,inhibiting particle aggregation,increasing the contact between particles and electrolyte,and shortening the Li⁺ion transport path.3)The composite material generated oxygen vacancies during the calcination process,resulting in the formation of partial Ti³⁺and Nb⁴⁺ions,which enhanced the electronic conductivity and ionic conductivity.In summary,TiNb₂O₇composite material with 5%MXene addition exhibited excellent electrochemical performance,demonstrating potential application prospects.