In the pursuit of high-performance solid-state batteries, the presence of an electrochemically stable solid electrolyte possessing an exceptional ionic conductivity exceeding 10 mS cm -1 is paramount. This remarkable attribute can be attained through the utilization of sulfide-based Na + solid ionic conductors . The class of materials denoted as Na 3 P nCh 4 represents another category of fast ion-conducting materials. These materials are characterized by the presence of isolated P nCh 4 tetrahedra arranged in a cubic structure.