Li+ ion conductivity and diffusion mechanism in α-Li3N and β-Li3N

Abstract

β-Li₃N of hexagonal D⁴_6h (P6₃/mmc) structure was synthesized by high-energy ball milling commercial Li₃N (composed of both α and β phases). Ionic conductivities of α-Li₃N and β-Li₃N were tested by direct current (D.C.) and alternating current (A.C.) impedance methods. β-Li₃N exhibited the same order of magnitude of Li⁺ ion conductivity (2.085 × 10⁻⁴ S cm⁻¹) as that of α-Li₃N (5.767 × 10⁻⁴ S cm⁻¹) at room temperature. First-principles calculations were employed to simulate the diffusion mechanism of Li⁺ ion in α-Li₃N and β-Li₃N. Our results indicate that the diffusion of Li⁺ ion in β-Li₃N likely occurs between pure Li_β(1) planes, which is different from that in α-Li₃N, where the diffusion of Li⁺ ion occurs within Li₂N plane. The Li⁺ ion migration energy barriers (E^m) for α-Li₃N and β-Li₃N are 0.007 eV and 0.038 eV, respectively.