Insights of the Ionic Transport in Intercalated Two-Dimensional Materials Leveraging Lattice Dynamics

Ionic transport in solids is a key factor in affecting battery performance. Inspired by the recent findings of the correlation between lattice dynamics and ionic transport, we conduct a more in-depth analysis of phonon spectra of ionic intercalation structures LixMoS2. In this paper, phonon dispersion curves and projected density of states of intercalation structures at different Li concentrations are calculated to compare with the corresponding migration barrier. The result shows that Li-dominated phonon modes are mainly distributed at the phonon gap of MoS2, and these modes tend to fill the gap at higher Li concentration. At the frequency range of these Li-dominated modes, the energy occupation of the migration ion is put forward as an appropriate descriptor that is found to be logarithmically related to the migration barrier. On the basis of the relationship, the Arrhenius formula for diffusion coefficient is modified and some parameters are estimated. Our study represents the power of the lattice dynamics in analyzing ionic transport, which can be used to distinguish the migration pattern and predict migration paths. Lattice dynamics provide the methodology to regulate ionic transport by phonon engineering and screen for better 2D materials.