Phonon-Ion Interactions: Designing Ion Mobility Based on Lattice Dynamics

This review is focused on the influence of lattice dynamics on the ionic mobility in superionic conductors in particular solid-state Li-ion conductors. After a succinct review of the static view of ionic conduction, the role of polarizability as the underlying cause of lattice softness is discussed in connection with the anharmonicity and the roles of lattice dynamics on ionic conductivity as proposed in early theories in the 70's and 80's by Mahan, Zeller, Rice and Roth are reviewed with the emphasis on various proposed correlations between Debye and Einstein frequency as well as other specific vibrational modes with the activation energy. The role of lattice dynamics on the correlation between the pre-exponential factor and activation energy, i.e. the Meyer-Neldel rule is also presented with emphasis on the entropy of migration and its dependence on the vibrational spectrum of the lattice. Moreover, a recent computational high-throughput screening based on the average vibrational frequency is also discussed to illustrate the application of lattice dynamics descriptors to design new lithium conductors. Finally, several open questions regarding the fundamental understanding of the role of lattice dynamics and new strategies to tune ionic conductivity based on these concepts are presented.