Ethanol-Based Solution Synthesis of a Functionalized Sulfide Solid Electrolyte: Investigation and Application

A sulfide solid electrolyte was synthesized using a solution-phase approach via the dissolution of Li₃PS₄ in ethanol followed by heat treatment (90–300 °C). This method yielded an electrolyte with a maximum lithium-ion conductivity of 1.7×10⁻⁵ S cm⁻¹ at 200 °C (down to 25 % of the pristine Li₃PS₄); however, increasing the heating temperature resulted in a significant decrease in conductivity. Nuclear magnetic resonance spectroscopy revealed the decomposition of the PS₄³⁻ unit into P₂S_x dimers (P₂S₇⁴⁻ and P₂S₆⁴⁻) at high temperatures. X-ray absorption spectroscopy further confirmed a core-shell structure in the solution-phase-synthesized electrolyte, with an enriched shell of oxygen-substituted P(S/O)_x phases. Both the P₂S_x dimers in the core and the oxygen-rich shell may have contributed to the reduction in lithium-ion conductivity. Moreover, the oxygen-rich shell unexpectedly suppressed undesirable side reactions at the solid electrolyte/cathode interface. This study demonstrates the functionalization of solution-phase synthesis for sulfide solid electrolytes from ethanol, with a trade-off between conductivity and interface stability. Further optimizing the heat treatment process and shell engineering are promising avenues for enhancing the performance of all-solid-state batteries.