Interfacial Stability and Li + Transport Trade‐Off in Halide‐Based SEI Components for LPSC: A First‐Principles Study

ABSTRACT The solid electrolyte interphase (SEI) formed from the decomposition of Li 6 PS 5 Cl (LPSC) is a critical determinant of performance and safety in all‐solid‐state lithium metal batteries. Herein, first‐principles calculations are employed to systematically investigate the interfacial stability and Li + transport properties of the main SEI components, including LiF, LiCl, LiBr, LiI, Li 2 S, and Li 3 P in contact with metallic lithium. The results show that F‐doping yields LiF interfaces with superior stability and passivation. LiF delivers the highest interfacial energy, the highest dendrite suppression ability, and the strongest electronic blocking (highest tunneling barrier) among lithium halides. F‐doping thus significantly enhances the SEI's mechanical integrity and electronic passivation, minimizing dendrite risk and parasitic reactions. Conversely, Br and I‐doped LPSC components (LiBr, LiI) improve Li + surface transport kinetics (lowest migration barriers) and interfacial adhesion, but at the expense of a reduced mechanical barrier and weaker electronic insulation. This study clarifies the fundamental trade‐off between interfacial stability and ion transport kinetics dictated by halogen identity. These theoretical insights provide crucial guidance for the rational design of composite SEI layers and the precise optimization of halogen doping concentrations in LPSC electrolytes.