Influence of synthesis parameters on the conductivity of pristine and Cl/Br‐doped Na ₃ PS ₄ solid electrolytes

Abstract The transition toward sustainable energy requires safe and efficient storage systems. Sodium‐ion batteries are a promising alternative to lithium‐based systems, with Na 3 PS 4 solid electrolytes gaining attention for their safety, processability, and ionic conductivity. This study investigates how synthesis parameters (e.g., heat treatment time) affect the conductivity of pristine and Cl − /Br − ‐doped Na 3 PS 4 . Electrolytes with nominal compositions Na 3 PS 4 , Na 3.0 PS 3.8 Cl 0.2 , and Na 3.0 PS 3.88 Br 0.12 were synthesized via ball milling and heat treatment, and characterized by X‐ray diffraction (with Rietveld refinement), scanning electron microscopy, and electrochemical impedance spectroscopy. Cl − doping with moderate heat treatment introduces Na⁺ vacancies, enhancing ionic conductivity fourfold (4.8×10 −5 Scm −1 ) without compromising phase stability. In contrast, Br − doping results in NaBr precipitation and reduced conductivity. These findings provide insights into the effect of halogen doping and synthesis conditions to understand structure–transport relationships, guiding the development of Na 3 PS 4 ‐based solid electrolytes. Based on that, future work should refine synthesis conditions and doping level to deepen the understanding and further improve ionic transport in solid‐state sodium‐ion batteries.