# 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

## TL;DR

This paper uses theoretical simulations to study how the composition of Li2S and Li3PS4 affects their interface structure in solid-state batteries.

## Contribution

The study reveals how compositional ratios influence Raman spectra and interfacial vibrational coupling in Li–S battery materials.

## Key findings

- The LPS/Li2S interface remains stable regardless of compositional ratios.
- Low content of LPS and Li2S emphasizes [PS4]3− vibrational modes in Raman spectra.
- Sufficient material content is needed to observe distinct interfacial vibrational coupling.

## Abstract

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.