Synthesis of Pyrochlore-type Li _1.25 La _0.58 Nb ₂ O ₆ F Solid Electrolyte via Spark Plasma Sintering

Oxide-based lithium-ion conductors are attractive due to their chemical stability. Among these, pyrochlore-type oxyfluorides have emerged as a solid electrolyte family with high ionic conductivity and strong water tolerance. However, their ionic conductivity remains lower than those of previously reported sulfide- and oxychloride-based solid electrolytes. In addition, sintered pellets exhibit poor densification, limiting lithium-ion transport. In this study, spark plasma sintering (SPS) was employed to prepare and densify pyrochlore-type Li 1.25 La 0.58 Nb 2 O 6 F solid electrolytes. SPS enables rapid synthesis within minutes compared to conventional solid-state synthesis and yields dense pellets with a relative density of 98%. Owing to the reduction of grain boundary resistance, the SPS-processed samples exhibited the highest bulk conductivity (15 mS cm –1 at 300 K) reported to date for oxide-based lithium-ion conductors. This study is significant in the development of oxide-based solid electrolytes, opening opportunities in a field long dominated by sulfide-, chloride-, and oxychloride-based systems.