Stability and Formation of the Li₃PS₄/Li, Li₃PS₄/Li₂S, and Li₂S/Li Interfaces: A Theoretical Study

Solid electrolytes have shown superior behavior and many advantages over liquid electrolytes, including simplicity in battery design. However, some chemical and structural instability problems arise when solid electrolytes form a direct interface with the negative Li-metal electrode. In particular, it was recognized that the interface between the β-Li₃PS₄ crystal and lithium anode is quite unstable and tends to promote structural defects that inhibit the correct functioning of the device. As a possible way out of this problem, we propose a material, Li₂S, as a passivating coating for the Li/β-Li₃PS₄ interface. We investigated the mutual affinity between Li/Li₂S and Li₂S/β-Li₃PS₄ interfaces by DFT methods and investigated the structural stability through the adhesion energy and mechanical stress. Furthermore, a topological analysis of the electron density identified preferential paths for the migration of Li ions.