K(3)SbS(4) as a Potassium Superionic Conductor with Low Activation Energy for K–S Batteries

Solid‐state K‐ion conducting electrolytes are key elements to address the current problems in K secondary batteries. Here, we report a sulfide‐based K‐ion conductor K(3)SbS(4) with a low‐activation energy of 0.27 eV. W‐doped K(3−x )Sb(1−x )W( x )S(4) (x=0.04, 0.06, 0.08, 0.10 and 0.12) compounds were also explored for increasing vacancy concentrations and improving ionic conductivity. Among them, K(2.92)Sb(0.92)W(0.08)S(4) exhibits the highest conductivity of 1.4×10(−4) S cm(−1) at 40 °C, which is among the best reported potassium‐ion conductors at ambient temperature. In addition, K(2.92)Sb(0.92)W(0.08)S(4) is electrochemically stable with long‐chained potassium polysulfide of K(2)S( x ). A room‐temperature solid potassium–sulfur (K−S) battery system has therefore been successfully demonstrated, which is the first K−S battery prototype using non‐commercial inorganic‐based electrolyte to block the polysulfide shuttle.