Sintering aid effect of La ₂ Zr _1.4 Ta _0.6 O ₇ /Li _6.4 La ₃ Zr _1.4 Ta _0.6 O ₁₂ nanocomposite in garnet‐type solid‐state electrolyte

Abstract Garnet‐type lithium lanthanum zirconium oxide is a promising solid electrolyte for lithium–oxygen batteries owing to its high ionic conductivity and stability against Li metal anodes. The development of novel sintering aids is crucial for achieving densification, grain growth, and the formation of Li conducting and mechanically strong grain interfaces, enabling ionic conductivity >10 −3 S/cm and long‐term stability. In this study, 120 nm composite nanoparticles of La 2 Zr 1.4 Ta 0.6 O 7 /Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 were synthesized via planetary ball milling of Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) microparticles followed by annealing under Ar atmosphere at 900°C. The presence of the La 2 Zr 1.4 Ta 0.6 O 7 layer and size effect in the composite nanoparticles facilitated the sintering of cubic LLZTO microparticles at 1160°C, resulting in improvement of ionic conductivity (3.9 × 10 −4 S/cm) and Vickers hardness (6.3 GPa) without significant particle growth. The mixing ratio of the composite nanoparticles was optimized at 20 wt%. Simulation of the nanoparticle arrangement on the microparticles with various mixing ratios revealed that adding 10‒20 wt% nanoparticles is essential to cover microparticles with a single layer, suppressing highly resistive grain boundary formation.