Study On The Sythesis Of Li₇La₃Zr₂O₁₂ Solid State Electrolyte And Its Stability In Air

All-solid-state lithium batteries have many advantages such as high safety,high energy density and high capacity density.In the research of solid electrolytes,the garnet-type Li₇La₃Zr₂O₁₂is one of the most promising candidates.Therefore,the preparation process of Li₇La₃Zr₂O₁₂was systemetically investigated and optimized in this paper.The effects of Al³⁺/Ta⁵⁺doping on phase formation,structure and ionic conductivity were investigated.We then analyzed the stability of Al-doped solid electrolyte in humid air and the effects of the Li⁺/H⁺ion exchange process.The effect of the sintering medium on the phase formation of the solid electrolytes was investigated.Al³⁺and Ta⁵⁺doped solid electrolyte powders were sintered using corundum and ordinary clay crucible for comparison,the effects of different sintering medium on the phase formation and structure were analyzed by combining XRD and NMR.It was found that the sintering effect of the corundum is better,so the corundum crucible is the suitable sintering medium to prepare the garnet-type solid electrolyte material.Garnet-type cubic Al³⁺/Ta⁵⁺-doped Li₇La₃Zr₂O₁₂were prepared by high temperature solid-state method.In the system of Li_7-3xAl_xLa₃Zr₂O₁₂,the optimal sintering condition has been determined as 1130?for 6 hours;and the Al³⁺occupied the Li⁺site in the lattice,with slightly reduced the unit cell parameter from 12.958 to12.952?.Li_6.1Al_0.3La₃Zr₂O₁₂had the highest ionic conductivity of 3.8×10^-4Scm^-1and the minimum activation energy of 0.31 eV.In the system of Li_7-xLa₃Zr_2-xTa_xO₁₂,the optimal sintering condition was 1120?for 7 hours,and the Ta⁵⁺occupied the Zr⁴⁺site in the lattice,which dramatically reduced the unit cell parameter from 12.958 to 12.915?.Li_6.4La₃Zr_1.4Ta_0.6O₁₂had the highest ionic conductivity of 4.9×10^-4Scm^-1and the minimum activation energy of 0.29 eV.considering influence of doping on material structure and ionic conductivity,the effect of Ta⁵⁺doping was more pronounced.The stability of solid electrolyte in humid air was studied,using the Li_7-3xAl_x La₃Zr₂O₁₂material as an example.Results of SEM and EDS confirmed that the irregular block structure layer formed on the surface was impurity Li₂CO₃.¹H,⁶Li,²⁷Al,¹⁷O MAS NMR and other results revealed that when samples were placed in a humid atmosphere,the amount of Li₂CO₃ and Al?OH?₃ increased along with the time of placement,while the amount of LaAlO₃ decreased.Results of ¹H-⁶Li CP MAS NMR showed that Li⁺located on 24 d was more likely to be replaced by portons from H₂O molecules.