Lithium ion conducting NaSICON materials: Migration mechanisms and energies

Abstract

Sodium superionic conductors (NaSICONs) have garnered significant attention as promising solid electrolytes for all-solid-state batteries, owing to their high ionic conductivity at room temperature. The ionic motion in these materials at the atomistic scale can be investigated by computational approaches such as Density Functional Theory (DFT) to gain deeper insights into their transport properties. In this work, we present a comprehensive review of DFT-based studies, focusing on site occupancies and transport mechanisms that govern the Li⁺ conduction in NaSICONs. The reported site and migration energies show significant variations, primarily attributed to differences in the size of the calculated supercells. Despite these discrepancies, our analysis confirms that both vacancy-assisted and interstitial migration occur in the NaSICON structure, with the latter being crucial for enabling superionic conduction. Therefore, a comprehensive understanding of the Li⁺ migration in NaSICONs requires consideration of both mechanisms as well as the various migration pathways involved.