Fabrication And Electrochemical Performance Of Li₄Ti₅O₁₂ Modified By Solid Electrolytes As Anode Materials For Lithium-ion Batteries

Energy is crucial to the development of science and technology,but the resources become scarce due to the undue use.Developing lithium ion batteries(LIBs)is one of the solutions for the present energy crisis.LIBs possess large energy density,high output voltage and friendliness toward environment.However,the anode materials used in current LIBs(dominantly carbon materials)could not meet the demands of many energy fields,especially electric vehicles and hybrid electric vehicles.In this paper,LTO was composited by different solid electrolytes synthesized though sol-gel method and the electrochemical performance was explored in some ways.(1)In order to simultaneously improve both the ionic and electronic conductivities,Li4Ti5O12(LTO)was composited with Li2ZrO3 accompanying with superficial Zr4+doping by the simple reaction between Zr(NO3)4·5H2O and LiNO3 on the LTO surface.From the comparative experiments,the as-modified LTO with a Li2ZrO3/LTO mass ratio of 0.009 and sintered at 750 ? exhibits the most excellent rate performance(achieving capacities of 155.3,149.6,145.4,139.6 and 130.2 mAh/g at 100,200,400,800 and 1600 mA/g,respectively)and long-term cyclability(retaining a capacity of 102 mAh/g after the 2000th cycle at 500 mAh/g).By the detailed structural characterization and electrochemical impedance spectra analysis,the formation of the tetragonal Li2ZrO3 with good ionic conductivity and the superficial Zr4+doping with improved electronic conductivity is responsible for the markedly enhanced cycling and rate performance of LTO.(2)Dual-phase Li4Ti5O12-TiO2(LTOT)was modified by the composite of lithium zirconates(Li6Zr2O7+Li2ZrO3,LZO)to boost the rate capabilities and cyclability.When the homogeneous mixture of LiN03,Zr(NO3)4·5H20 and LTOT was sintered at 700 ? for 5 h,the as-prepared composite achieved a higher reversible capacity of 183.2 mAh/g than the pure Li4Ti5O12 after cycling at a current density of 100 mA/g for 100 times due to the presence of a small amount of TiO2.Meanwhile,when the composite was cycled at 100,200,400,800 and 1600 mA/g for every 10 cycles,the reversible capacities are 183.2,179.1,176.5,173.3 and 169.3 mAh/g,respectively,suggesting the excellent rate performance.Even cycled at 500 mA/g for 1400 times,the composite still retained a reversible capacity of 144.7 mAh/g,revealing the appreciable cycling stability.From a series of comparative experiments and systematic characterizations,the formation of LZO not only meliorates the ionic conductivity of LTOT,but also improves the electronic conductivity due to the concomitant superficial Zr4+ doping,giving rise to the comprehensive enhancement in electrochemical performance of LTO.(3)Li1.3Al0.3Ti1.7(PO4)3(LATP)is a Li-ion conductive solid electrolyte with high ionic conductivity,meanwhile,it also possesses relatively high electronic conductivity compared to the other fast ionic conductors.LATP was composited with Li4TiO12(LTO)at a mass ratio of 0.026 and calcined at 700 ? for 5 h.The composite delivers reversible capacities of 164.8,156.3,152.4,146.5 and 130.5 mAh/g at the current densities of 100,200,400,800 and 1600 mA/g,respectively,as well as a capacity of 112 mAh/g after cycling at 500 mA/g for 1200 cycles.The appreciable performance is attributable to the three-dimensional Li-ion diffusion channels in LATP to facilitate Li-ion migration,and the local charge imbalance resulted from the substitution of Al3+for Ti4+ to promote charge transfer in LTO,thus the LATP-composited LTO exhibits enhanced ionic and electronic conductivities,as well as the markedly boosted electrochemical performance.