Study On The Modification Of Li₄Ti₅O₁₂ With Carbon And Nitrogen As The Anode Material Of Lithium Ion Batteries

With the exhaustion of non-renewable energy and the increasingly serious problems of environment,the need for clean and efficient energy storage device has directed a global trend.Lithium ion battery is an auspicious candidate for the application of electric vehicles due to their high energy density,cycling stability and no memory effect.Electrode materials play a decisive role in the performance of lithium ion battery.Spinel and zero-strain Li₄Ti₅O₁₂exhibits a long cycle life,satisfactory safety,a flat and relatively high lithium insertion/extraction voltage avoided the formation of dendritic lithium,so it becomes one of the most promising anode materials of lithium ion batteries.However,the large scale application of Li₄Ti₅O₁₂ has been limited due to its low electronic conductivity,which results in fading of capacity during cycling and severely polarization at high charge and discharge rate.This dissertation focuses on improving the electronic conductivity of Li₄Ti₅O₁₂ by coating and doping with carbon and nitrogen to enhance the electrochemical performance by ball milling assisted with high temperature solid state method.The main research contents are as follows:Melamine formaldehyde resin?MF?,polyacrylonitrile?PAN?and Polyaniline?PANI?are used as carbon and nitrogen sources for the modification of Li₄Ti₅O₁₂.X-ray diffraction?XRD?,scanning electron microscopy?SEM?and electrochemical testing are employed to characterize the structure,morphology and electrochemical behaviors of the samples,respectively.The results indicate that PANI-LTO-1-20 modified by PANI with the mass ratio of PANI and Li₄Ti₅O₁₂?coating ratio?at 1:20 shows the best electrochemical behaviors among the modified samples treated by the three different carbon and nitrogen sources.The discharge capacity of the PANI-LTO-1-20 sample reaches 94.1 m Ah·g^-1at 10 C.After 100 cycles at 10C,its capacity retention keeps at 97.2%.TiO₂ and Li₂CO₃ are used to synthesis the pure Li₄Ti₅O₁₂.The selected carbon and nitrogen source of PANI is added for the modification of Li₄Ti₅O₁₂ by direct coating to obtain the LTCN samples and the LCNT samples by pre-coating TiO₂.XRD,X-ray photoelectron spectroscopy?XPS?and Raman spectrum analysis are used to characterize the structure of the samples;SEM and transmission electron microscope?TEM?are used to characterize the morphology;lithium ion coin cells are assembled for the testing of electrochemical behaviors.The performance of the carbon coated Li₄Ti₅O₁₂ is characterized for comparison.The comparison between the LTCN and LCNT samples indicates that the samples synthesized by pre-coating TiO₂ exhibit better performance.XRD results show that the diffraction peaks of all modified samples are indexed to the spinel Li₄Ti₅O₁₂.The central position of main peaks move towards the direction of low angle indicating some atoms might be doped in the Li₄Ti₅O₁₂ lattice.The results of XPS and Raman confirm the formation of coated carbon and Ti-N bond.The results of constant current charging-discharging indicate that LCNT-2 obtained by pre-coating process of TiO₂ shows the best rate capacity when the coating ratio is 1:20 with the discharge capacity of 140.5 mAh·g^-1 at 10 C.After 100 cycles at10 C,its capacity retention keeps at 97.8%.