Strain Effect and the Li-ion Transport Mechanism in the Li6PS5Cl Superionic Conductor from Molecular Dynamics Simulations

Extensive experimental and computational studies have been reported on various Li-ion electrolytes but the mechanism of the long-range ion transport for solid state cationic superconductors remains largely unexplained. We report here our results on (LAMMPS+UFF+QEq) molecular dynamics simulations with applied electric fields to explain both cationic and anionic diffusion mechanisms leading to Li-superionic conductivity in Li6PS5Cl. We report that Li migration occurs via conjugated substitutional type diffusion involving rearrangements of three or more Li-ions in a 3D matrix of anions that are essentially stationary for temperatures below 350 K. The predicted Li-ion conductivity for single phase Li6PS5Cl is 4.6 mS/cm is in good agreement with solid state NMR measurements of 4.9 mS/cm. We reported an activation energy of 0.2 eV within experimentally reported range. We also reported a sharp melting point at 450.3 K. Further, we have shown strain engineering can not only be used to enhance room temperature Li-ion conductivity but also creates “Li-superconductor highway”.