Preparation And Study On Electrochemical Lithium Storage Behavior Of Nb-Based Oxides

With the wide application of lithium ion batteries in electric vehicles and other fields,it is important to find anode materials with high power density and good safety for lithium ion batteries.The rate performance of graphite materials used in commercial lithium ion batteries is generally poor,Li₄Ti₅O₁₂ has been suggested as a promising alternative to graphite for its excellent high rate properties and cycle stability.However,its low specific capacity leads to low energy density,which limits its application in batteries.TiNb₂O₇,a novel anode material with a structure ReO₃ has both excellent rate performance and higher specific capacity,however,there are still many challenges to overcome,such as poor electronic conductivity and poor cycle stability.Up to now,only few researches were done in this area,so further studies still need to be done.Both the crystal structure characteristics of TiNb₂O₇ and the kinetics of lithium ion insertion were studied to explore the relationship between the two-dimensional lithium-ion diffusion channel and the lithium ion transport.The results suggest that the pure TiNb₂O₇ negative electrode has high specific capacity,good cycle stability,high magnification performance and long cycle stability.The primary conductivity of the material under different SOC was calculated by using the first principle calculation.The intrinsic conductivity of the material found in different SOC was improved with the increase of the amount of lithium intercalation.After the synthesis analysis,the intercalation mechanism of lithium ions in the phase pure material is put forward,that is,the active substance near the current collector reacts first in the electrochemical reaction,which affects the electrochemical reaction of the active material away from the current collector,resulting in a large loss of irreversible capacity.The effects of different calcination temperatures?900?,1000?,1100?and1200??on the structure,morphology and electrochemical properties of TiNb₂O₇oxides were investigated.The results showed that by increasing the calcination temperature,the crystal structure of TiNb₂O₇ oxide did not change,while the oxide particles increased gradually;and the crystallinity increased.The effects of different calcination temperatures on the electrochemical properties of the composites were investigated.It was found that TiNb₂O₇-1200 showed the highest specific capacity and cycle stability under the charge and discharge rates at 0.1C and 1C.TiNb₂O₇-1100 and TiNb₂O₇-1200 show better electrochemical performance than TiNb₂O₇-900 and TiNb₂O₇-1000.The capacity retention ratio of 2000 cycles is higher than 90%at 5C and10C rates.TiNb₂O₇ nanorods with one-dimensional nanostructures were synthesized by liquid phase method.The results show that the material grows along the?003?crystal plane during the growth process,which is favorable for the rapid transmission of lithium ions in the interior,resulting in excellent magnification performance and long cycle performance.Ti₂Nb₁₀O₂₉ nanospheres with porous hierarchical structure were synthesized by solvothermal method.The porous nanospheres exhibited a uniform particle size distribution?between 300-500 nm?,and the primary particles showed a rod or rod-like structure,with the growth of a particular crystal face.The results show that the super-magnification performance and long-cycle stability are mainly due to the high specific surface area of the porous graded structure,which provides a high contact area of the electrode/electrolyte.The hierarchical structure makes the lithium ion de-insertion occurs on a primary particle of tens of nanometers,greatly reducing the diffusion distance of lithium ions.Moreover,the Ti₂Nb₁₀O₂₉ nanospheres with porous grading show a significant pseudostructure effect during charge and discharge,and play a decisive role in their high magnification capacity,and also ensure that they exhibit high capacity retention ratio during the long cycles.Three-dimensional ordered macroporous structures based on PS microsphere templates were used to synthesize highly ordered 3DOM T-Nb₂O₅ and 3DOM-TiNb₂O₇oxides.3DOM T-Nb₂O₅ and 3DOM-TiNb₂O₇ oxides show a nanoscale pore structure on the three-dimensional ordered skeleton,and the unique three-dimensional ordered structure,together with the pore structure on the skeleton,is favorable for producing high electrode/electrolyte active contact area,is conducive to the electrochemical intercalation of lithium.At the same time,the three-dimensional hierarchical pore structure is favorable for the storage and exchange of electrolyte,reducing the concentration polarization,increasing the electrochemical reaction kinetics and enhancing the magnification performance of the electrode material.While the defective structure of the nanopores on the skeleton can provide additional lithium ion storage location to enhance the reversible capacity of the material,even beyond its theoretical capacity.It is found that the pseudo-capacitance effect plays an important role in the high rate capacity of the 3DOM T-Nb₂O₅ and 3DOM-TiNb₂O₇ oxides.With the increase of charge and discharge rate,which is mainly due to the high specific surface area characteristic brought by the three-dimensional graded joint structure,highlighting its significance in the fast charge-discharge performance.