Study On Preparation And Modification Of Li₄Ti₅O₁₂ Anode Material

Spinel Li₄Ti₅O₁₂,as anode material for lithium ion battery,exhibits good stability,good electrochemical security,and long cycling life,making it as a potential anode material for high power lithium ion batteries.However,the low electric conductivity of Li₄Ti₅O₁₂does lead to the poor rate capability at high rates.In this paper,in order to enhance the rate capabilities of the spinel Li₄Ti₅O₁₂,the Mg²⁺and F^-co-doped Li₄Ti₅O₁₂ and Zr⁴⁺and F^-co-modified Li₄Ti₅O₁₂ were synthesized by solid-state reaction in situ and ex situ,respectively.The structure and electrochemical performance of the material were investigated by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,energy dispersive spectroscopy?EDS?,transmission electron microscope?TEM?,X-ray photoelectron spectroscopy?XPS?,electrochemical impedance spectroscopy?EIS?,and galvanostatic charge-discharge tests.The research work finished and the results obtained are listed as following:Mg²⁺-modified and F^--modified Li₄Ti₅O₁₂ were prepared by solid-state reaction in situ.The results of tests showed that the crystal of Li₄Ti₅O₁₂ had not been changed after Mg²⁺and F^-modifing,and it had a smaller primary particles with a narrow size distribution,higher initial discharge capacity and lower resistance of the electrode.The optimal mass ratio of Mg²⁺and F^-modifing are 3mol%and 2mol%,respectively,and Mg²⁺and F^-co-modified Li₄Ti₅O₁₂ was prepared at the ratio.The Mg²⁺and F^-co-modified technique improved effectively rate capabilities and cycling stabilities of the Li₄Ti₅O₁₂ electrodes.The discharge capacity of Mg²⁺and F^-co-modified Li₄Ti₅O₁₂ was 174.6 mAh·g^-1,170.2mAh·g^-1,162.1 mAh·g^-1,140.1 mAh·g^-1,121.8 mAh·g^-1 and 94.7 mAh·g^-1 at 0.2C,0.5C,1C,3C,5C and 10C,respectively,increasing by 15.8%,24.4%,31.3%,49.8%,59.8%and80.7%compared to the pure Li₄Ti₅O₁₂,and 120.3 mAh·g^-1 at 5C after 150 cycles with a capacity retention of 98.8%,increasing by 48 mAh·g^-1 and 15.6%compared to the pure Li4Ti5O12.Zr⁴⁺and F^-co-modified Li₄Ti₅O₁₂ was prepared by solid-state reaction ex situ.The results of tests showed that the Li₄Ti₅O₁₂ material had a holonomic spinel structure after Zr⁴⁺and F^-co-modified,and there was no ZrF₄ coating layer on the surfaces of Li₄Ti₅O₁₂particles,instead that F^-reacted with Li₄Ti₅O₁₂ chemically to generate new impurity phase of LiF and anatase TiO₂,while Zr⁴⁺formed amorphous ZrO₂.According to the results of electrochemical performance tests,Zr⁴⁺and F^-co-modified technique was effective in extending the voltage plateau,enhancing the rate capabilities,reducing the resistance and increasing cycling performance of Li4Ti5O12 material.The discharge capacity of 1wt%ZrF₄-modified Li₄Ti₅O₁₂ was 171.1 mAh·g^-1?154.1 mAh·g^-1?141.0 mAh·g^-1?104.6mAh·g^-1?86.7 mAh·g^-1 and 66.7 mAh·g^-1 at 0.2C,0.5C,1C,3C,5C and 10C,respectively,increasing by 6.9%?10.3%?15.9%?30.8%?40.3%?61.5%compared to the pure Li₄Ti₅O₁₂,and 80.7 mAh·g^-1 at 5C after 150 cycles with a capacity retention of 91.5%,increasing by27.8 mAh·g^-1 and 3.3%compared to the pure Li₄Ti₅O₁₂.