A Theoretical Raman Spectra Analysis of the Effect of the Li2S and Li3PS4 Content on the Interface Formation Between (110)Li2S and (100)β-Li3PS4

In this study, we perform density functional theory (DFT) simulations to investigate the Raman spectra of the bulk and surface phases of β-Li3PS4 (LPS) and Li2S, as well as their interfaces at varying compositional ratios. This analysis is relevant given the widespread application of these materials in Li–S solid-state batteries, where Li2S functions not only as a cathode material but also as a protective layer for the lithium anode. Understanding the interfacial structure and how compositional variations influence its chemical and mechanical stability is therefore crucial. Our results demonstrate that the LPS/Li2S interface remains stable regardless of the compositional ratio. However, when the content of both materials is low, the Raman-active vibrational mode associated with the [PS4]3− tetrahedral cluster dominates the interface spectrum, effectively obscuring the characteristic peaks of Li2S and other interfacial features. Only when sufficient amounts of both LPS and Li2S are present does the coupling between their vibrational modes become sufficiently pronounced to alter the Raman profile and reveal distinct interfacial fingerprints.