Electrochemical Performance And Structure Of Multiion Co-doped Li₄Ti₅O₁₂

The spinel Li4Ti5O12 has been investigated as a lithium ion anode material owning to its advantage such as good cycling stability,good reversibility,no structural change(zero-strain structure material)and Li+ has a three dimensional diffusion channel in the charge-discharge for lithium-ion batteries.However,its rate performance is limited,because the electronic conductivity and Lithium-ion difusion coefficient are much lower.This is also the reason of this thesis.In this work,multiion co-doped Li4Ti5O12 was prepared by wet milling assisted solid-state method with a subsequent air treatment.X-ray diffraction(XRD),scanning electron microscopy(SEM),cyclic voltammograms(CV),and electrochemical impedance spectra(EIS)were used to study the effects of ion doping on the stucture,morphology,and electrochemical properties.Three groups of compound ions doping including in Br--Mg2+?Br--K+?Br--Al3+,are successfully introduced into the Li4Ti5O12 lattice,and formed solid solution,The unit cell volume was increased,which can increase the amount of Ti3+/Ti4+ mixing as charge compensation,and Lithium ion diffusion coefficient was much enlarger,so they can effectivetly increase and improve the electrochemical performance of Li4Ti5O12 at high rate and low temperature.Among the doped materials,Li3.8Mg0.2Ti5O11.8Br0.2 exhibits an outstanding electrochemical performance.it delivers a discharge capacity of 139.6 mAhg-1 with an capacity retention rate of 96.07%after 55 cycles at 10C rate at-20?,which is 46.38 mAhg-1 higher than the pure Li4Ti5O12,and at room temperature,the sample delivers a discharge capacity of 140.52 mAhg-1,an capacity retention rate of 97.61%after 100 cycles at 30C rate,at 25 0C.The significantly improved the electrochemical performance of the rate,cycle stability and discharge capacity could be attributed to the appropriate co-doping with Mg2+ and Br-,which has the lagest cell volume,lagest amount of Ti3+/Ti4+mixing as charge compensation,the minimum of charge transfer resistance and Warburg resistance,and the fastest of electronic conductivity and lithium ion diffusion coefficient.