A lattice-dynamics study of the cubic ${\mathrm{Li}}_3\mathrm{OCl}$ antiperovskite, a candidate solid electrolyte in lithium-ion batteries, reveals the presence of dynamical instabilities with respect to rotations of the ${\mathrm{Li}}_6\mathrm{O}$ octahedra. Calculated energy landscapes in the subspace of unstable octahedral rotational modes are very shallow with at most a 1 meV per formula unit reduction in energy upon breaking the cubic symmetry. While ${\mathrm{Li}}_3\mathrm{OCl}$ is not stable relative to decomposition into ${\mathrm{Li}}_2\mathrm{O}$ and LiCl at 0 K, estimates of the vibrational free energy suggest that ${\mathrm{Li}}_3\mathrm{OCl}$ antiperovskite should become entropically stabilized above approximately 480 K.

• Received 20 April 2015
• Revised 2 June 2015

DOI:https://doi.org/10.1103/PhysRevB.91.214306