Bulk Properties of Hong-Type NASICON as Solid Electrolyte: Vacancy Formation and Migration

Abstract

Theoretical study on Hong-type NASICON electrolyte was performed to investigate the structural stability and ion migration. Four types of NASCION structure were constructed according to the ratio of Si and P (i.e., Si3, Si2P, SiP2, P3). Starting from Na4Zr2Si3O12, P was doped on tetrahedral Si site, and one Na was eliminated to maintain charge neutrality. Because there are many Si/P and Na sites, we substitute Si to P and eliminate Na in primitive unit cell to effectively reduce the number of cases. Then, we calculated the vacancy formation energies for all elements of NASICON and migration of Na ion. The result shows that the formation tetrahedral Si/P vacancy was relatively easy in all types of NASICON. Especially, the P vacancy induced the dumbbell shape of oxygen configuration, which could block the path of Na migration. Separately, Na migration at the path 2->3 or 3->2 was estimated to be the dominant migration with the lowest energy barrier in all types of NASICON.