Real-time vibrational fingerprinting of liquid-phase sulfide electrolyte synthesis via in situ Raman spectroscopy

Abstract

All-solid-state lithium batteries benefit from scalable routes to sulfide solid electrolytes with controlled phase formation. Here, an in situ Raman spectrometer integrated with a microwave reactor provides real-time vibrational fingerprints of the liquid-phase reaction between Li₂S and P₄S₁₀ in acetonitrile. We benchmark the cell by tracking P₄S₁₀ solubility up to 130 °C and establish analytical performance for the PS stretch at ∼716 cm⁻¹, determining LOD = 0.78 mM and LOQ = 2.60 mM. Time-resolved spectra capture the systematic decay of the 716 cm⁻¹ band during the reaction, consistent with the disruption of the P₄S₁₀ cage and formation of thiophosphate intermediates. Early-stage kinetics are quantitatively described by the Finke–Watzky two-step model, and temperature-dependent rate constants yield Arrhenius and Eyring relationships with E_a(mw) = 39.59 kJ mol⁻¹, ΔH^‡ = 36.97 kJ mol⁻¹, and ΔS^‡ = −178.55 J mol⁻¹ K⁻¹. This combined in situ spectroscopic–kinetic approach offers a direct pathway to mechanistic understanding and parameter extraction in solution-based synthesis of sulfide SSEs.