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_2.98Sb_0.91S_3.53Cl_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 K₃SbS₄, marking the highest reported ionic conductivity for non-oxide potassium SEs. Solid-state ³⁹K magic-angle-spinning nuclear magnetic resonance on K_2.98Sb_0.91S_3.53Cl_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_2.98Sb_0.91S_3.53Cl_0.47 as a promising SE for all-solid-state potassium batteries.