Enhanced Li-ion transport in Li₁₀Sn_0.2Si_0.8P₂S₁₂ solid electrolytes through controlled SiO₂-induced oxysulfide modification

Sulfide-based solid electrolytes are promising candidates for all-solid-state lithium batteries because of their high Li⁺ conductivity and favorable mechanical processability, but their transport properties are highly sensitive to local structure, phase evolution, and surface chemistry. In this study, xSiO₂-modified Li₁₀Sn_0.2Si_0.8+xP₂S₁₂O_2x (x = 0, 0.2, 0.4, 0.6, and 0.8) solid electrolytes were prepared by high-energy milling and subsequent heat treatment, and the effect of SiO₂ content on structural and electrochemical properties was investigated using electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). EIS results show a non-monotonic composition dependence, with the x = 0.4 composition exhibiting the highest room-temperature ionic conductivity of approximately 2.6 × 10⁻³ S cm⁻¹. Arrhenius analysis further confirms that the x = 0.4 composition has the lowest activation energy of about 21 kJ mol⁻¹, indicating the most favorable Li⁺ migration pathway among the investigated compositions. Li symmetric-cell and critical current density (CCD) tests further show that the x = 0.4 composition exhibits lower polarization and a higher CCD of 1.02 mA cm⁻² than the x = 0 composition. XRD and Raman analyses show that moderate SiO₂ addition largely preserves the sulfide/thiophosphate framework, whereas higher SiO₂ contents increase structural disorder and heterogeneity. XPS analysis reveals enhanced Si–O–S/M–O-related surface environments for the x = 0.4 composition without complete conversion to an oxide-dominated phase. These results suggest that controlled SiO₂ incorporation provides an effective approach for modifying the local chemical environment while preserving the sulfide framework, which is consistent with the improved ionic conductivity and electrochemical properties observed in the present study.