Corner-Sharing PS4–BS4 Modes Facilitate Fast Ion Conduction in Lithium Thioborophosphate Iodide Glassy Solid Electrolytes

The amorphous nature and absence of grain boundaries in glassy solid electrolytes (GSEs) make them highly attractive for applications in all-solid-state lithium batteries (ASSLBs), leading candidates for next-generation energy storage technologies. A recently developed lithium thioborophosphate iodide GSE, composed of 30Li₂S-25B₂S₃-45LiI-5P₂S₅ (LBPSI), has demonstrated excellent room-temperature ionic conductivity and low activation energy. Despite this exciting finding, the underlying mechanism behind this ultrafast ion transport remains ambiguous. Here, we accurately fine-tune the foundational MACE-MP-0 model and perform large-scale machine learning molecular dynamics simulations to investigate the structural and ion dynamics in LBPSI GSE. Our results reveal that B₂S₃ glass formers primarily form multibridged B_xS_y long-chain networks that impede Li⁺ conduction. In contrast, P₂S₅ gives rise to monotetrahedral PS₄^3- and ditetrahedral P₂S₇^4-, which engage in distinctive corner-sharing modes with BS₄^5- tetrahedra, effectively disrupting the B_xS_y chains and enhancing Li⁺ mobility. Furthermore, the polyhedral anion rotations of PS₄^3- and BS₄^5- in the corner-sharing PS₄-BS₄ motifs further promote fast Li⁺ conduction.