Sodium Superionic Conductors Based on Clusters.

Owing to the high abundance and low cost of sodium (Na), Na-based rechargeable batteries hold great potential for large-scale applications in the future energy industry. However, as key component of the battery electrolyte, only a few Na-based superionic conductors can reach the ionic conductivity comparable to that of liquid or gel electrolytes. Here, we provide a guideline for the development of cluster-based Na-rich antiperovskite superionic conductors using computational studies. With a selected cluster ion BCl4-, we are able to achieve high-room-temperature Na-ionic conductivity over 10-3 S/cm and low activation energies below 0.2 eV in the antiperovskite crystals Na3S(BCl4) and Na3S(BCl4)0.5I0.5. In addition, these materials have large bandgaps and favorable mechanical properties. A comprehensive study of the stability and formation energy of these materials further illustrates possible routes for their synthesis. New insights into the conduction mechanism of these cluster-based superionic conductors are provided, including the cooperative motion of Na ions and the significant reduction of the migration barrier due to the changing orientation of the cluster ion.