Design Principles for Cation‐Mixed Sodium Solid Electrolytes
Zhuoying Zhu, Hanmei Tang, Ji Qi, Xiang‐Guo Li, Shyue Ping Ong
Abstract
Abstract All‐solid‐state sodium‐ion batteries are highly promising for next generation grid energy storage with improved safety. Among the known sodium superionic conductors, the Na 3 PnS 4 family and the recently discovered Na 11 Sn 2 PnS 12 (Pn = P, Sb) have garnered major interest due to their extremely high ionic conductivities. In this work, comprehensive investigation of the Na 3 PnS 4 ‐Na 4 TtS 4 (Pn = P/As/Sb, Tt = Si/Ge/Sn) phase space of superionic conductors using density functional theory calculations, as well as AIMD simulations on the promising new Na 11 Sn 2 PnS 12 (Pn=P/As/Sb) structures are presented. Crucial design rules on the effect of cation mixing are extracted on relative phase stability, electrochemical stability, moisture stability, and ionic conductivity. In particular, it is shown that while larger cations can substantially improve the ionic conductivity and moisture stability in these structures, there is an inherent trade‐off in terms of electrochemical stability. Na 11 Sn 2 AsS 12 is also identified as a hitherto unexplored stable sodium superionic conductor with higher Na + conductivity and better moisture stability than the Na 11 Sn 2 PS 12 and Na 11 Sn 2 SbS 12 phases already reported experimentally.