This investigation explores the fabrication of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) electrolytes, specifically focusing on the evolution of densification and resulting stress within the sintered structure of LLZTO electrolytes. Through a combination of experimental methods and numerical simulations based on finite element analysis, this study clarifies the mechanisms underlying the enhanced densification and grain growth of LLZTO with the addition of the sintering aid, liquid metallic gallium, attributing these effects to the reduced activation energies. With elevated sintering temperatures or the addition of gallium, the fired LLZTO exhibits heightened conductive performance, with conductivity increasing from < 10−4 to > 10−4 S cm−1. The numerical simulations further elucidate the correlation between stresses and the agglomeration/distribution of components during sintering. Non-uniform component distribution and agglomeration significantly escalate stress levels by two to four orders, compromising the structural integrity of the sintered electrolytes. The imperative need to address these challenges in the early stages of battery fabrication becomes apparent for the successful developments of ceramic electrolytes and the corresponding solid-state lithium batteries. Display omitted