Preparation and Characterization of Cation-Substituted Na₃SbS₄ Solid Electrolytes

Abstract

To realize all-solid-state sodium-ion batteries, the ionic conductivities and stabilities of solid electrolytes must be improved. The sulfide Na 3 SbS 4 electrolyte is known to show a high sodium-ion conductivity of over 10 −3 S cm −1 at room temperature. In this study, cation-substituted Na 3 SbS 4 solid electrolytes with excess Na or Na vacancies were prepared, and the effects of substitution on the material conductivity were examined. The ionic conductivities of the Na 3+x Sb 1−x M x S 4 (M = Si, Ge, Sn) electrolytes, which were doped with excess Na, were lower than that of the Na 3 SbS 4 electrolyte; in contrast, the conductivities of the Na 3−x Sb 1−x Mo x S 4 electrolytes, which were doped with Na vacancies, were higher. The Na 2.88 Sb 0.88 Mo 0.12 S 4 electrolyte showed the highest room-temperature ionic conductivity of 3.9 × 10 −3 S cm −1 and the lowest activation energy for conduction of 21 kJ mol −1 . To improve the ionic conductivity of the Na 3 SbS 4 electrolyte, introducing Na vacancies instead of excess Na was found to be effective.

Insights into the rich polymorphism of the Na+ ion conductor Na3PS4 from the perspective of variable-temperature diffraction and spectroscopy

“…At the same time, the Na3PS4 structural archetype has proven to be a fertile playground for materials design through elemental substitutions, defining a wider materials family of the general composition Na3PnCh4 (Pn: pnictogens P, As, Sb; Ch: chalcogens S, Se) 16,17,[26][27][28][29][30][18][19][20][21][22][23][24][25] ; receptive to various aliovalent substitutions, e.g. Ca 2+ on the sodium sites 31 , Clon the chalcogenide site i [32][33][34][35] , and Si 4+ or W 6+ on the pnictide site [36][37][38][39][40][41][42][43][44] . Notable compositions of the Na3PS4 structural family include Na3SbS4 with a room-temperature conductivity of the order of 10 -3 S/cm and distinct stability against ambient moisture 20,21,30 , and the recently reported tungsten-doped Na3-xWxSb1-xS4 with room-temperature Na + -conductivity of the order of 10 -2 S/cm 39,40 , currently the highest reported among polycrystalline Na + and Li + conductors.…”

Energy Storage Materials for Solid‐State Batteries: Design by Mechanochemistry

“…[ 147,148 ] When comparing solid‐state synthetic approaches and ball milling, it was shown that Mo can be introduced in Na 3 SbS 4 using mechanochemical milling, whereas a solid‐state synthesis does not lead to a Mo incorporation, suggesting that milling does have an additional influence on the phase stability of these highly substituted materials. [ 147,149 ] A different type of disorder of sodium within the structure, where the compound still resembles the nominal composition, but has partially vacant sodium positions, with interstitial positions being slightly occupied by the missing sodium is discussed in a theoretical work by Zhu et al, [ 143 ] where it is shown that this type of disorder significantly boosts the electrochemical performance. This general idea of introducing disorder in the mobile species substructure might be the reason, why the mechanochemically synthesized compounds usually have a better ionic conductivity, as it has been previously reported for different materials.…”

Visualization of Solid‐State Synthesis for Chalcogenide Na Superionic Conductors by in‐situ Neutron Diffraction

“…Similar with Na 3 PS 4 conductor, Na 3 SbS 4 also displays polymorphs that include tetragonal structure ( F 43 m space group) at room temperature and cubic structure ( P 421 c space group) at elevated temperatures [17,18] . There are many studies on the Na 3 SbS 4 family conductors regarding the interface stability against Na metal, [19–22] doping chemistry (i. e., W, Ge, Cl, Se), [23–26] and electrochemical performance [27,28] . When S is partially replaced by a large anion such as Se, Na 3 SbS 4‐ x Se x conductors show changes in the crystal structure from tetragonal Na 3 SbS 4 to cubic Na 3 SbSe 4 at room temperature [29] .…”