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 P2Sx 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 P2Sx 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 performance in all‐solid‐state batteries.