Reduced Energy Barrier for Li⁺ Transport Across Grain Boundaries with Amorphous Domains in LLZO Thin Films

The high-resistive grain boundaries are the bottleneck for Li⁺ transport in Li₇La₃Zr₂O₁₂ (LLZO) solid electrolytes. Herein, high-conductive LLZO thin films with cubic phase and amorphous domains between crystalline grains are prepared, via annealing the repetitive LLZO/Li₂CO₃/Ga₂O₃ multi-nanolayers at 600 °C for 2 h. The amorphous domains may provide additional vacant sites for Li⁺, and thus relax the accumulation of Li⁺ at grain boundaries. The significantly improved ionic conductivity across grain boundaries demonstrates that the high energy barrier for Li⁺ migration caused by space charge layer is effectively reduced. Benefiting from the Li⁺ transport paths with low energy barriers, the presented LLZO thin film exhibits a cutting-edge value of ionic conductivity as high as 6.36 × 10⁻⁴ S/cm, which is promising for applications in thin film lithium batteries.