Superionic Conduction in K3SbS4 Enabled by Cl‐Modified Anion Lattice

All‐solid‐state potassium batteries emerge as promising alternatives to lithium batteries, leveraging their high natural abundance and cost‐effectiveness. Developing potassium solid electrolytes (SEs) with high room‐temperature ionic conductivity is critical for realizing efficient potassium batteries. In this study, we present the synthesis of K 2.98 Sb 0.91 S 3.53 Cl 0.47 , showcasing a room‐temperature ionic conductivity of 0.32 mS/cm and a low activation energy of 0.26 eV. This represents an increase of over two orders of magnitude compared to the parent compound K 3 SbS 4 , marking the highest reported ionic conductivity for non‐oxide potassium SEs. Solid‐state 39 K magic‐angle‐spinning nuclear magnetic resonance on K 2.98 Sb 0.91 S 3.53 Cl 0.47 reveals an increased population of mobile K + ions with fast dynamics. Ab initio molecular dynamics (AIMD) simulations further confirm a delocalized K + density and significantly enhanced K + diffusion. This work demonstrates diversification of the anion sublattice as an effective approach to enhance ion transport and highlights K 2.98 Sb 0.91 S 3.53 Cl 0.47 as a promising SE for all‐solid‐state potassium batteries.