High Sodium Ion Mobility of PEO‐NaTFSI‐Na3Zr2Si2PO12 Composite Solid Electrolyte for All‐Solid‐State Na‐S Battery

Abstract A composite solid electrolyte based on PEO‐NaTFSI (polyethylene oxide‐sodium bis(trifluoromethanesulfonyl)imide) and Na 3 Zr 2 Si 2 PO 12 is fabricated for all‐solid‐state Na−S battery (ASSB). When the molar ratio of EO (ethylene oxide of PEO) to Na + (sodium ion of NaTFSI) is 20 and the amount of Na 3 Zr 2 Si 2 PO 12 is 30 wt%, a highest ionic conductivity of 3.14×10 −4 S cm −1 and the sodium ion transference number of 0.66 are achieved at 60 °C. Harnessing the electrolyte's improved sodium ion transport abilities enables ASSB's assembled with a sulfur cathode and sodium metal anode to exhibit highly reversible current‐rates and capacity retention. At 0.2 C and 60 °C, the battery delivers a superior discharge capacity of 1110.0 mAh g −1 in the first cycle and maintains 666.8 mAh g −1 after 60 cycles with a stable Coulombic efficiency near 100 %.