Preparation And Properties Of W-based Double Doped Garnet Li₇La₃Zr₂O₁₂ Solid Electrolyte

At present,lithium-ion batteries have been widely used in energy storage systems such as portable electronic products,electric vehicles,smart grids and solar power generation.The liquid electrolyte used in commercial lithium-ion batteries has the risk of combustion,and the use of solid electrolyte is expected to fundamentally improve the safety of lithium-ion batteries.The garnet-type LLZO solid electrolyte not only has high ionic conductivity and extremely low electronic conductivity,but also has good chemical stability and wide electrochemical window.This paper focuses on how to synthesize samples with high lithium ion conductivity.The effects of different composition,sintering temperature and sintering time on the structure,microstructure and electrochemical properties of solid electrolyte ceramics were studied.Li_7-2y+xLa_3-xBa_xZr_2-yW_yO₁₂（0≤x≤0.06）precursor powders were synthesized by solid state reaction method at 900℃ for 6 h.Li_7-2y+xLa_3-xBa_xZr_2-yW_yO₁₂（0≤x≤0.06）ceramics were obtained by sintering at 1180℃ for 6 h.XRD diffraction patterns show that the crystal structure of Ba-W co-doped ceramics is cubic phase structure.Ba-W co-doping can stabilize the cubic phase at room temperature.A small amount of pores can be observed between the grains of the undoped Ba sample(Li_6.4La₃Zr_1.7W_0.3O₁₂),and abnormal grains can be observed.After adding Ba（x=0.04）,the grains gradually grow and become denser.The Li_6.42La_2.98Ba_0.02Zr_1.7W_0.3O₁₂ ceramic sample has the best performance.The relative density of the sample can reach 91.8%,the total ionic conductivity is 2.23×10^-4 S cm-1（30℃）,and the corresponding activation energy is0.28 e V.Li_7-3x-2yGa_xLa₃Zr_2-yW_yO₁₂（0≤y≤0.2）ceramic powders were synthesized by solid state reaction method at 900℃ for 6 h.Li_7-3x-2yGa_xLa₃Zr_2-yW_yO₁₂（0≤y≤0.2）ceramics were obtained by sintering at 1180℃ for 6 h.The XRD diffraction pattern shows that the crystal structure of Ga-W co-doped ceramics is cubic phase structure.It can be explained that Ga-W double doping can effectively stabilize the cubic phase at room temperature.The microstructure shows that many pores can be observed between the grains of the sample(Li_6.7Ga_0.1La₃Zr₂O₁₂)without W doping,and the sintering is not dense enough.When the introduction amount of W is 0.15 mol,the pores between the grains of the sample are significantly reduced,and the sintering is very dense.The Li_6.4Ga_0.1La₃Zr_1.85W_0.15O₁₂ ceramic sample has the best performance.The relative density of the sample can reach 93.4%,the total ionic conductivity is 3.03×10^-4 S cm^-1（30℃）,and the corresponding activation energy is 0.26 e V.