Synergistic Effect of Ga-Based Precipitates and Ga-Au Surface Layer on Stabilization of Li₇La₃Zr₂O₁₂ Solid Electrolyte

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is a promising oxide solid electrolyte with high ionic conductivity and excellent stability toward Li metal. However, the presence of grain boundaries (GBs) cause a decrease in the ionic conductivity and cycling stability of the sintered LLZO. Herein, we promote the Ga precipitation at GBs through excessive doping with Ga/Al/Ta, simultaneously depositing a few nanometers thickness Au layer to form a Ga-Au surface layer. High-temperature sintering of heavily doped LLZO induces Ga precipitation, effectively filling the GB of the pellet. Consequently, the relative density and ionic conductivity are increased. Furthermore, nanoscale Au encounters precipitated Ga and forms a new Ga-Au layer, which reduces the contact resistance. The new layer prevents direct contact between molten Li and Ga-based composites at the GBs, thus enhancing the cycling stability. Therefore, it demonstrates the synergistic effect that the precipitated Ga improves the compactness of the LLZO electrolyte, whereas the Ga-Au layer enhances the cycling stability. It provides a straightforward approach to address the issues originated from GBs and increase the cycling stability of LLZO, thereby contributing to the practical application of all-solid-state batteries.