Na 2 MgP 2 S 6: A new solid electrolyte for sodium ion batteries

Transparent needles -like single crystals of Na 2 MgP 2 S 6 were obtained by self -flux synthesis route from Na 2 S, Mg, and P 2 S 5 . The crystal structure of the new compound was determined from single -crystal X-ray diffraction data [ wR ( F 2 ) = 0.066, 1088 reflections, 58 variables]. The chemical composition was confirmed by energy dispersive X-ray spectroscopy (EDX), and the ionic conductivity was measured using electrochemical impedance spectroscopy (EIS). Na 2 MgP 2 S 6 crystallizes in the orthorhombic system, space group Pbcn (N degrees 60), a = 7.3629 (3) A, b = 21.5547 (8) A , c = 6.2155 (3) A, V = 986.43 (7) A 3 and Z = 4. The sulfur atoms form a distorted hexagonal close packing within which the sodium, magnesium, and P -P dimer units are octahedrally coordinated and form a honeycomb -like structure. Two of the three sodium atomic positions are partially occupied. Na 2 MgP 2 S 6 exhibits an ionic conductivity of 8.8x10 -7 S cm - 1 ( E a = 0.48 eV) at 29.6 degrees C.