Mechanistic Insights into Li+ Transport Enabled by Isolated Sulfur Species in Li3PS4 Glasses

Abstract

All-solid-state lithium-ion batteries have renewed interest in high-performance solid electrolytes. Li3PS4 (Li2S-P2S5) glasses are among the most studied due to their high ionic conductivity, traditionally ascribed to rotational motion of polyhedral units facilitating Li+ migration. Using ab initio molecular dynamics, we investigate Li-ion diffusion in Li3PS4 glass, demonstrating that our structural model reproduces experimental neutron and X-ray diffraction patterns and conductivity measurements. Importantly, we identify a previously unrecognized diffusion mechanism: Li+ ions near isolated sulfur species (Sn with n = 1, 3) display significantly enhanced mobility, with atomic displacements up to 1.7 greater than those associated with bulkier polyhedral units. These results highlight the critical role of free sulfur species in promoting fast ionic transport, providing insights for the rational design of glass compositions with optimized conductivity for solid-state battery applications