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 30Li 2 S-25B 2 S 3 -45LiI-5P 2 S 5 (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 B 2 S 3 glass formers primarily form multibridged B x S y long-chain networks that impede Li + conduction. In contrast, P 2 S 5 gives rise to monotetrahedral PS 4 3– and ditetrahedral P 2 S 7 4–, which engage in distinctive corner-sharing modes with BS 4 5– tetrahedra, effectively disrupting the B x S y chains and enhancing Li + mobility. Furthermore, the polyhedral anion rotations of PS 4 3– and BS 4 5– in the corner-sharing PS 4 –BS 4 motifs further promote fast Li + conduction.