Computational discovery of stable Na-ion sulfide solid electrolytes with high conductivity at room temperature

Abstract

The search for inorganic solid electrolytes suitable for the realization of solid-state batteries with structural stability and high ion conductivity at room temperature remains a significant challenge. In this study, we employed a multi-stage density functional theory molecular dynamics (DFT-MD) sampling workflow, focusing on Na-ion sulfides with trivalent (M) and pentavalent (M′) metal ions and an expanded selection of parent structures (Ω). This led to the identification of two promising sampling spaces (M,M′,Ω) = (Ga,P,Na₄SiS₄) and (Si,Ta,Na₄SiS₄). The predictions were validated through multi-temperature DFT-MD calculations, wherein σ_Na,300K ≳ 10⁻³ S cm⁻¹ are attained within a thermodynamic phase stability range of 9 < E_hull < 25 meV per atom (E_hull is convex hull decomposition energy): Na₄Ga_0.5P_0.5S₄, Na_3.75Ga_0.375P_0.625S₄, Na_4.25Ga_0.625P_0.375S₄, Na_3.75Si_0.75Ta_0.25S₄, Na_3.625Si_0.625Ta_0.375S₄, and Na_3.5Si_0.5Ta_0.5S₄. These compounds are highly suggested for experimental synthesis and investigation. Moreover, our brute-force and highly generalized sampling technique is expected to be applicable in uncovering other solid electrolyte classes, thus potentially contributing to the advancement of solid-state battery technology.