Improvement of the Li-ion conductivity and air stability of the Ta-doped Li₇La₃Zr₂O₁₂ electrolyte via Ga co-doping and its application in Li-S batteries

The garnet-type solid electrolyte Li₇La₃Zr₂O₁₂ (LLZO) has emerged as a promising candidate for all-solid-state lithium-ion batteries (ASSLBs) due to its exceptional performance. However, it currently faces challenges related to low ionic conductivity and structural instability, which limit its widespread application. To obtain a garnet-type solid electrolyte with high ionic conductivity and stable structure, Ta and Ga co-doped Li_6.6−3xGa_xLa₃Zr_1.6Ta_0.4O₁₂ (Gax-LLZT) was successfully synthesized using a solid-phase method. The influence of Ga-doping on crystal structure, morphology, relative density, ionic conductivity, and air stability was investigated. The results indicate that Ga-doping not only alters the Li occupancy distribution, enhancing ionic conductivity but also expedites the densification of the garnet electrolyte, reducing the required sintering temperature for densification. Specifically, Ga0.1-LLZT sintered at 1050 °C for 6 h achieves a relative density of 95.3% and a total ionic conductivity of 8.09 × 10⁻⁴ S cm⁻¹ at 25 °C. Remarkably, it exhibits excellent air stability, retaining 86% of the initial total ionic conductivity after 4 months of atmospheric exposure. Furthermore, the Li|Ga0.1-LLZT|Li symmetric cell demonstrates excellent Li metal stability. The fabricated Li|Ga0.1-LLZT|S-KB full cell maintains a discharge specific capacity of 392 mA h g⁻¹ after 600 cycles at 0.1C, confirming the potential of the Gax-LLZT electrolyte in ASSLBs.