Halogen Doping in Na3PS4 Solid Electrolytes for High Performance All-Solid-State Sodium Batteries

Sulfide-based solid electrolytes are promising for all-solid-state sodium batteries due to their high ionic conductivity and facile processability, but their practical use is limited by moisture sensitivity and poor interfacial stability. To address these issues, Na3−xPS4−xMx (M = F, Cl, Br, I) electrolytes were first synthesized as a preliminary study to evaluate the effect of halogen doping. Chlorine was identified as the most effective dopant and was therefore selected for a systematic investigation of doping concentration. Na3−xPS4−xClx (x = 0.1–0.3) electrolytes were prepared by solid-state sintering, and the optimum composition was determined to be Na2.85PS3.85Cl0.15, which achieved a high ionic conductivity of 5.5 × 10−4 S·cm−1 with a reduced activation energy of 33.3 kJ·mol−1. When employed in TiS2|Na2.85PS3.85Cl0.15|Na3Sn full cells, the optimized electrolyte enabled high initial capacity, excellent rate capability, and stable long-term cycling. These results highlight the effectiveness of Cl doping concentration control in enhancing both the intrinsic properties of Na3PS4-based electrolytes and the overall electrochemical performance of all-solid-state sodium batteries.