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

TL;DR

This study reveals that isolated sulfur species in Li3PS4 glasses significantly enhance Li+ ion mobility, offering new insights into designing better solid electrolytes for lithium-ion batteries.

Contribution

The paper uncovers a novel diffusion mechanism involving isolated sulfur species that improves ionic conductivity in Li3PS4 glasses.

Findings

Li+ ions near isolated sulfur species show up to 1.7 times greater displacement.

Structural model matches experimental diffraction and conductivity data.

Isolated sulfur species play a critical role in fast ionic transport.

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