Computational and experimental investigation of Na₄P₂S₆ as a promising solid electrolyte material for sodium metal batteries

Recent experiments¹ have shown that Na₄P₂S₆, prepared from a hydrated precursor Na₄P₂S₆●6H₂O by heating under vacuum to 175 deg. C, has good ionic conductivity and stability with respect to metallic Na anodes, suggesting its promise as a solid state electrolyte for Na ion batteries. Examining the experimental results, we have extended previous computational work² on this material to further understand its structural, conductivity, and interface properties. Of particular interest is the observation^1,3 that Na₄P₂S₆ crystallizes to form monoclinic crystals having the space group C2/m which is distinct from the hexagonal or trigonal structures^4-6 analyzed for the related material Li₄P₂S₆. Computer modeling results suggest that the C2/m structure of Na₄P₂S₆ is stabilized by lattice vibrations.
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¹Hood et al. Manuscript in preparation. ²Rush et al. SSI 286, 45-50 (2016). ³Kuhn et al. Z. Anorg. Allg. Chem. 640, 689-692 (2014). ⁴Mercier et al. Solid State Chem. 82, 151-162 (1982). ⁵Hood et al. SSI 284, 61-70 (2015). ⁶Neuberger et al. Dalton Trans. 47, 11691-11695 (2018).