Improved Air Stability of Li Argyrodites Through PS43− Rotation Suppression by Al and Se Co-Substitution for All-Solid-State Batteries

Abstract

Sulfide-based solid electrolytes, particularly Li argyrodites, hold significant promise for practical all-solid-state batteries (ASSBs); however, their poor stability under humid conditions presents a critical challenge. Despite numerous efforts to address this issue, a comprehensive mechanistic understanding of moisture-induced degradation remains limited. Herein, we introduce an Al and Se co-substituted argyrodite, Li<inf>6-3</inf><inf>x</inf>Al<inf>x</inf>PS<inf>5-1.5</inf><inf>x</inf>Se<inf>1.5</inf><inf>x</inf>Cl, which enhances both the Li+ conductivity and air stability. The optimized composition (x = 0.05) exhibits an improved Li+ conductivity of 4.91 mS cm−1 at 30 °C and a 22% conductivity reduction after dry-air exposure (dew point: −40 °C for 5 h), compared with 3.71 mS cm−1 and a 42% decrease for the unsubstituted sample. Reduced surface degradation is validated by comprehensive experimental analyses. Complementary calculations indicate less favorable H<inf>2</inf>O adsorption and further reveal that Al and Se co-substitution inhibits the rotation of P[S<inf>2</inf>SeO]3− and P[S<inf>2</inf>O<inf>2</inf>]3−; tetrahedra via preferential surface-oriented Se2− and Al─O interactions, which otherwise promote H<inf>2</inf>O-induced degradation, thereby minimizing moisture interactions. Finally, the improved electrochemical performance of the co-substituted argyrodite is validated by its enhanced capacity retention following air exposure in NCM|Li<inf>6</inf>PS<inf>5</inf>Cl|(Li-In) cells. This study highlights rotational dynamics as an overlooked mechanism underlying moisture-induced degradation, and demonstrates that targeted co-substitution is a viable strategy for advancing practical ASSBs. © 2025 The Author(s). Advanced Science published by Wiley-VCH GmbH.