Synthesis conditions affecting electrochemical and chemical stabilities of Ga-doped Li7La3Zr2O12 solid electrolyte

All-solid-state lithium batteries with Li metal anodes and solid-state electrolytes (SSEs) can achieve higher energy density and enhanced safety compared to the current liquid-based Li-ion batteries. Among several SSEs, Li₇La₃Zr₂O₁₂ (LLZO) has attracted attention due to its high Li⁺ ion conductivity (∼10⁻³ S cm⁻¹ at room temperature for Ga-doped LLZO) and good stability in ambient air. However, the challenges of Li penetration and the chemical instability against Li are the primary obstacles to its practical application. This study investigates the effects of the grain size and electronic conductivity of Ga-doped LLZO on the critical current density (CCD). Using samples with similar interfacial impedances between Ga-doped LLZO and Li, we demonstrate that a decrease in the grain size of Ga-doped LLZO lowers the electronic conductivity, leading to a higher CCD. Furthermore, although a previous study suggests that Ga-doped LLZO might be unsuitable for direct contact with Li, the chemical stability against Li is enhanced in a more compact pellet prepared at a higher cold-pressing pressure. These results underscore the significance of the sintering conditions and pellet pressing pressure in the synthesis of Ga-doped LLZO since they ultimately affect the electrochemical and chemical stabilities of the Ga-doped LLZO solid electrolyte with a Li-metal anode.