Elastic properties of diverse sodium-ion conductive materials: a first-principles study

Abstract

All-solid-state sodium batteries are expected to be low-cost energy-storage devices because they use resource-rich sodium. However, mechanical degradation remains a critical issue, and solid electrolytes must exhibit sufficient ductility to accommodate the expansion and contraction of the electrode active materials at their interface. In this study, the elastic properties of various sodium-ion conductors were evaluated using first-principles calculations and compared based on their anion elements, compositions, crystal phases, and other factors. The elastic moduli of approximately 40 sodium-ion conductors were calculated. The results revealed that sulfide-, chloride-, and hydride-based materials generally exhibit low elastic moduli, whereas oxide materials exhibit higher values. Among the evaluated sulfide compounds, β-Na₃PS₄ crystals exhibit a relatively high Pugh's ratio, suggesting sufficient ductility to resist mechanical degradation. Furthermore, Na_2.875Sb_0.875W_0.125S₄ exhibited lower elastic moduli and higher Poisson's and Pugh's ratios than Na₃SbS₄. Unsupervised clustering of the bulk and shear moduli identified two distinct categories of oxide electrolytes: those with medium elastic moduli and those with large elastic moduli. Notably, NaAl₁₁O₁₇ exhibited the highest elastic modulus and Pugh's ratio among all the ox electrolytes, which was attributed to its high oxide ion concentration. A nonlinear correlation was observed between the elastic moduli and the mean atomic volume across most materials; however, hydrides deviated from this trend, exhibiting low elastic moduli despite their small mean atomic volumes.