Effect of Doping and Defect on Hong-Type NASICON Structure: First-Principle Study

Abstract

NASICON is a well-known yet pursuing candidate for the usage of solid electrolyte material. Unfortunately, fundamental information on stability and efficiency of Na ion migration in NASICON is little known. Here, we employed density functional theory (DFT) calculation to aim to fill in the theoretical knowledge gap on the Hong-type NASICON. Four types of NASCION structure were constructed according to the ratio of Si and P (i.e., Si3, Si2P, SiP2, P3). From a starting material Na4Zr2Si3O12, P was doped on tetrahedral Si site and one Na was eliminated to maintain charge neutrality. Note that we substituted Si to P and eliminated Na in primitive unit cell to reduce the number of doping cases effectively. On those systems, the vacancy formation energies for the atom elements in NASICON and migration barrier of Na ion were estimated. The results showed that the formation of tetrahedral Si/P vacancy was relatively easy in all types. Especially, the P vacancy induced the dumbbell shape configuration of oxygens, which could block the path of Na migration.Also, Na migration in the path of [100] direction was expected to be dominant because of the low energy barrier.