Nanoscaled Na₃PS₄ Solid Electrolyte for All-Solid-State FeS₂/Na Batteries with Ultrahigh Initial Coulombic Efficiency of 95% and Excellent Cyclic Performances

Nanosized Na3PS4 solid electrolyte with an ionic conductivity of 8.44 × 10-5 S cm-1 at room temperature is synthesized by a liquid-phase reaction. The resultant all-solid-state FeS2/Na3PS4/Na batteries show an extraordinary high initial Coulombic efficiency of 95% and demonstrate high energy density of 611 Wh kg-1 at current density of 20 mA g-1 at room temperature. The outstanding performances of the battery can be ascribed to good interface compatibility and intimate solid-solid contact at FeS2 electrode/nanosized Na3PS4 solid electrolytes interface. Meanwhile, excellent cycling stability is achieved for the battery after cycling at 60 mA g-1 for 100 cycles, showing a high capacity of 287 mAh g-1 with the capacity retention of 80%.