Interface formation by composite electrolytes using Li7La3Zr2O12 / Li2OHBr for bulk-type sintering-free oxide-based all-solid-state batteries

Garnet-type crystalline Li₇La₃Zr₂O₁₂ (LLZs) is an oxide-based electrolyte (SE) that exhibits high ionic conductivity at room temperature. However, the LLZs green compact exhibits a remarkably low conductivity owing to the challenges in deforming LLZ particles using solely cold-pressing. Therefore, the ionic conduction path becomes extremely narrow in point contact, resulting in increased grain boundary resistance. We proposed the realization of a green compact with high ionic conductivity and a large area by combining the antiperovskite-like crystal Li₂OHBr as a soft SE and LLZs as a highly conductive hard SE. In this study, highly lithium-ion-conductive composites of LLZs and antiperovskite-like crystal Li₂OHBr were prepared using ball milling. The composite powders were then palletized via uniaxial pressing at room temperature. Cross-sectional scanning electron microscopy images of the green compact revealed the presence of Li₂OHBr phases in the voids of LLZs particles. The total conductivity of the obtained 30 vol% Li₂OHBr-LLZ green compact was 7.1 × 10⁻⁵ S cm⁻¹ at 60 °C. Moreover, sintering-free oxide-based all-solid-state battery was successfully fabricated using the 50 vol% Li₂OHBr-LLZs composite and LiFePO₄ to obtain a reversible capacity of approximately 90 mAh g⁻¹.