Interfacial Enhancement of an Iodide-Oxide-Sulfide Solid Electrolyte for Long-Life All-Solid-State Lithium Metal...

Interfacial instability against lithium metal remains a major challenge for sulfide-based solid electrolytes in all-solid-state lithium metal batteries (ASSLMBs). In this study, the previously reported iodide-oxide-sulfide solid electrolyte 10LPSOI was prepared by mechanical ball milling (BM) and a modified liquid-phase shaking (LS) method to investigate the influence of the synthesis route on structural characteristics, particle morphology, ionic transport, and lithium-metal interfacial behavior. Structural and spectroscopic analyses revealed differences in phase characteristics and local phosphorus environments between 10LPSOI-BM and 10LPSOI-LS, while SEM analysis showed that the LS method produced substantially finer and more homogeneous particles. Although 10LPSOI-LS exhibited a lower room-temperature ionic conductivity of 0.7 mS cm^-1 than 10LPSOI-BM at 3.4 mS cm^-1, it achieved a higher critical current density of 0.925 mA cm^-2 compared with 0.30 mA cm^-2 for 10LPSOI-BM. The Li | 10LPSOI-LS | Li symmetric cell maintained relatively stable polarization for about 3092 h at 0.30 mA cm^-2 before a sustained decrease in overpotential was observed. In addition, 10LPSOI-LS showed improved cycling stability in NMC₁₁₁-based cells compared with 10LPSOI-BM under the tested conditions. These results indicate that the modified LS route improves lithium-metal interfacial performance despite the lower ionic conductivity. This improved behavior is correlated with synthesis-dependent differences in particle morphology, phase characteristics, local structure, and surface chemistry. The modified liquid-phase process may also offer potential advantages for scalable preparation of sulfide-based solid electrolytes.