High densification and Li-ion conductivity of Al-free Li7-xLa3Zr2-xTaxO12 garnet solid electrolyte prepared by using ultrafine powders

摘要

Ta-doped Li7La3Zr2O12 (Ta-LLZO) is considered as a promising solid electrolyte due to high Li-ion conductivity and good chemical stability against electrode materials. In this work, Ta-LLZO was prepared by a conventional solid-state reaction. Ultrafine powders were obtained by ball-milling to improve the surface activity. Ta-LLZO is sintered in ZrO2 crucibles to avoid introducing Al into the samples. The particle size distribution, phase structure, morphology, ionic conductivity, electronic conductivity, density and electrochemical performance of semisolid battery were characterized by laser diffraction particle size analyzer, X-ray diffraction, scanning electron microscope, AC-impedance, DC polarization, Archimedes method and a battery testing system, respectively. The results show that the ball milling to reduce the particle size is an effective way to solve the problem of relatively low density and Li-ion conductivity for Al-free Li7-xLa3Zr2-xTaxO12. For Al-free Li7-xLa3Zr2-xTaxO12, the increase of x (0.2 = x = 0.4) promotes the grain growth and sintering densification, but the increase of x (0.4 x = 0.6) has an adverse effect. Li6.7La3Zr1.7Ta0.3O12 sintered at 1180 degrees C for 12 h shows the relative density of 92% and the highest Li-ion conductivity of 1.03 x 10(-3) S/cm at 30 degrees C with the activation energy of about 0.37 eV, while Li6.6La3Zr1.6Ta0.4O12 sintered at 1180 degrees C for 12 h shows the highest relative density of 96% and the Li-ion conductivity of 6.68 x 10(-4) S/cm at 30 degrees C with the activation energy of about 0.46 eV. The electronic conductivity of Al-free Li7-xLa3Zr2-xTaxO12 is 10(-9) S/cm orders of magnitude. The semi-solid battery shows the first discharge capacity of 104.6 mAh/g and 92.5% capacity retention after 20 cycles.