Exploring electronic and ionic transport properties of promising electrolyte Na2ZnS2 for all-solid-state sodium-ion battery

Solid-state electrolyte (SSE) with high ionic conductivity and low cost is essential for accelerating the commercialization of all-solid-state sodium-ion batteries. Here, we provide profound atomistic insights into electronic and ionic transport properties of the SSE candidate Na2ZnS2 using the highly accurate first-principles calculations. Our calculations demonstrate that orthorhombic Na2ZnS2 exhibits dynamical and mechanical stabilities with ductility and a wide electrochemical stability window from 0.93 to 1.98 V. We find a direct bandgap of 3.80 eV from GW calculation and low electron/hole conductivities at low carrier concentrations, verifying its electronic insulating behavior. From machine learning interatomic potential-based molecular dynamics simulations, we obtain a high ionic conductivity of 1.93 mS/cm at 300 K with a low activation energy of 0.24 eV, highlighting the practicality of Na2ZnS2 for SSE applications.