Composite Electrolyte for All-Solid-State Lithium Batteries: Low-Temperature Fabrication and Conductivity Enhancement

All-solid-state lithium batteries offer notable advantages over conventional Li-ion batteries with liquid electrolytes in terms of energy density, stability, and safety. To realize this technology, it is critical to develop highly reliable solid-state inorganic electrolytes with high ionic conductivities and adequate processability. Li_1+x Al_x Ti_2-x (PO₄ )₃ (LATP) with a NASICON (Na superionic conductor)-like structure is regarded as a potential solid electrolyte, owing to its high "bulk" conductivity (ca. 10^-3  S cm^-1 ) and excellent stability against air and moisture. However, the solid LATP electrolyte still suffers from a low "total" conductivity, mainly owing to the blocking effect of grain boundaries to Li⁺ conduction. In this study, an LATP-Bi₂ O₃ composite solid electrolyte shows very high total conductivity (9.4×10^-4  S cm^-1 ) at room temperature. Bi₂ O₃ acts as a microstructural modifier to effectively reduce the fabrication temperature of the electrolyte and to enhance its ionic conductivity. Bi₂ O₃ promotes the densification of the LATP electrolyte, thereby improving its structural integrity, and at the same time, it facilitates Li⁺ conduction, leading to reduced grain-boundary resistance. The feasibility of the LATP-Bi₂ O₃ composite electrolyte in all-solid-state Li batteries is also examined in this study.