Preparation Of Doped Li₇La₃Zr₂O₁₂ Solid Electrolyte By Molten Salt Method

Garnet lithium ion solid electrolyte Li₇La₃Zr₂O₁₂（LLZO）has many advantages,such as high ionic conductivity,easy preparation,low cost,good stability and safety,but its conductivity needs further improvement compared with liquid electrolyte.Therefore,how to improve its conductivity has become a research hotspot.Li5.96Al0.2La3Zr1.69W0.25Y0.06O12,Li5.82Al0.2La2.98Ba0.02Zr1.55Y0.1O12,Li7-2x Cux La3Zr2O12（0.25<x<0.45）,Li_6.3-2yCu_0.35La₃Zr_2-yW_yO₁₂（0<y<0.6）and Li_6.3+zCu_0.35La_3-zY_zZr₂O₁₂（0≤z≤0.4）were prepared by molten salt method,respectively.The products were characterized by AC impedance,X-ray diffraction,scanning electron microscopy and X-ray fluorescence spectroscopy.The effects of molten salt type,pre-sintering temperature,sintering temperature,molten salt content and powder content on the conductivity,crystal structure,microstructure,relative density and shrinkage of the product were studied.The stability of Li_6.3Cu_0.35La₃Zr₂O₁₂in air was tested.The main research results are as follows:1)The optimum technological conditions for preparing Li_5.96Al_0.2La₃Zr_1.69W_0.25Y_0.06O₁₂solid electrolyte are as follows:molten salt is Li₂CO₃-Li OH,pre-sintering temperature is 850C,sintering temperature is 1140 C.Under these conditions,the ionic conductivity of the solid electrolyte at room temperature is3.31×10^-4S·cm^-1,the relative density is 91.4%,and the shrinkage rate is 6.8%.2)The optimum technological conditions for the preparation of Li_7-2xCu_xLa₃Zr₂O₁₂（0.25<x<0.45）solid electrolyte are as follows:x=0.35,molten salt Li2CO3-Li OH,excessive20wt%,pre-sintering temperature 550℃,sintering temperature 1160℃and buried powder 4G.Under these conditions,the ionic conductivity of the solid electrolyte is 5.61 x 10-4 S cm-1,the cubic garnet structure has 94.5%relative density,0.27e V activation energy and 8.9%shrinkage.Cu exists in the form of Cu²⁺in Li_6.3Cu _0.35La₃Zr₂O₁₂solid electrolyte.3)Li_6.3-2yCu_0.35La₃Zr_2-yW_yO₁₂solid electrolyte prepared at y=0.4 has ionic conductivity of 7.13×10^-4S·cm^-1,cubic garnet structure,relative density of 95.9%and shrinkage of 10.6%.Li_6.3+zCu_0.35La_3-zY_zZr₂O₁₂solid electrolyte was prepared at z=0.2.Its ionic conductivity was5.93×10^-4S·cm^-1,cubic garnet structure,relative density was 95.0%,and shrinkage was 9.3%.4)The conductivity of Li_6.3Cu_0.35La₃Zr₂O₁₂drops to 4.83×10^-4S·cm^-1after 2 weeks in air.There is no phase change and no impurity formation.After 3 months of storage,the conductivity decreased to 8.97×10^-5S·cm^-1,and there was no phase transition and Li₂CO₃ appeared.5)Innovation:The pre-sintering and sintering temperature of Li_5.96Al_0.2La₃Zr_1.69W_0.25Y_0.06O₁₂were reduced by molten salt method,and the pre-sintering temperature of Li_6.3Cu_0.35La₃Zr₂O₁₂was reduced.Cu²⁺doped Li₇La₃Zr₂O₁₂,Cu²⁺and W⁶⁺co-doped Li₇La₃Zr₂O₁₂and Cu²⁺and Y³⁺co-doped Li₇La₃Zr₂O₁₂solid electrolytes have not been reported.