Vacancy‐Controlled Na⁺ Superion Conduction in Na₁₁Sn₂PS₁₂

Abstract

Highly conductive solid electrolytes are crucial to the development of efficient all-solid-state batteries. Meanwhile, the ion conductivities of lithium solid electrolytes match those of liquid electrolytes used in commercial Li ion batteries. However, concerns about the future availability and the price of lithium made Na ion conductors come into the spotlight in recent years. Here we present the superionic conductor Na Sn PS , which possesses a room temperature Na conductivity close to 4 mS cm , thus the highest value known to date for sulfide-based solids. Structure determination based on synchrotron X-ray powder diffraction data proves the existence of Na vacancies. As confirmed by bond valence site energy calculations, the vacancies interconnect ion migration pathways in a 3D manner, hence enabling high Na conductivity. The results indicate that sodium electrolytes are about to equal the performance of their lithium counterparts.

Finding the Right Blend: Interplay Between Structure and Sodium Ion Conductivity in the System Na5AlS4–Na4SiS4

“…Similar to the LGPS system (Kamaya et al, 2011;Bron et al, 2013Bron et al, , 2016Kuhn et al, 2013aKuhn et al, ,b, 2014Kato et al, 2014Kato et al, , 2016Hori et al, 2015a,b;Harm et al, 2019), tetrel elements were employed in the Na 3+x T x P 1-x S 4 (T = Si, Sn) system to increase the charge carrier density and increase the overall ionic conductivity. The Sn-containing compounds are structurally very similar to the LGPS-like Li 10 SnP 2 S 12 and show conductivities of 4 · 10 −5 S cm −1 for Na 10 SnP 2 S 12 and the highest measured sodium ionic conductivity at room temperature for sulfides of 4 · 10 −3 S cm −1 for Na 11 Sn 2 PS 12 (Bron et al, 2013;Richards et al, 2016;Duchardt et al, 2018). Aliovalent silicon substitution studies were also conducted for the Na 3 PS 4 phase achieving a maximum conductivity of 7.4 · 10 −4 S cm −1 for a glass ceramic of composition 94(Na 3 PS 4 ) · 6(Na 4 SiS 4 ) .…”

Studies of Functional Defects for Fast Na‐Ion Conduction in Na3−yPS4−xClx with a Combined Experimental and Computational Approach

“…As a reference, the activation energy for most solid electrolytes is >0.24 eV. [2,14,15] The achieved small activation energy in t-Na 3−x PS 4−x Cl x is beneficial for flexible adaption of these solid electrolytes to be used in different climates especially at low temperatures with no significant decrease in ionic conductivity.…”

Ionic Conductivity of the NASICON‐Related Thiophosphate Na1+xTi2−xGax(PS4)3

“…Continued research on Na + conducting thiophosphates has focused on compounds derived from Li 10 GeP 2 S 12 . Namely, the Ceder group was able to synthesize Na 10 SnP 2 S 12 with a high ionic conductivity of 4.0×10 −5 S cm −1 ,and Na 11 Sn 2 PS 12 has recently been found separately by the groups of Roling and Nazar, with an even higher conductivity in the range of mS cm −1 . In addition to the Li 10 GeP 2 S 12 derived structures, recent work has also focused on Na‐Sb‐S compounds for ionic conductors …”

“…Namely,t he Ceder group was able to synthesize Na 10 SnP 2 S 12 with ah igh ionic conductivity of 4.0 10 À5 Scm À1 , [35] and Na 11 Sn 2 PS 12 has recently been found separately by the groups of Roling and Nazar,w ith an even higher conductivity in the range of mS cm À1 . [36][37][38] In addition to the Li 10 GeP 2 S 12 derived structures, recent work has also focusedo nN a-Sb-Sc ompounds for ionic conductors. [39] Herein, in an effort to further widen the materials space of sodium ion conductors,t he Na + ionic conductivity of the thio-NASICON analogue NaTi 2 (PS 4 ) 3 (NTPS) and the effects of Gasubstitution in Na 1 + x Ti 2Àx Ga x (PS 4 ) 3 are explored.…”