Manipulating the Defect Formation in Na₄OI₂ Anti-Perovskite for High-Performance Solid-State Electrolyte Applications

Recently, Na-based anti-perovskites (NaAP) show promising potential as solid-state electrolytes (SSEs) in battery applications due to their high safety and low cost. As the ionic and electrical conductivity of NaAP can be significantly influenced by the defect properties of the host, this study employs first-principles calculations to investigate the defect properties of two-dimensional (2D) anti-perovskites Na₄OI₂ and explores strategies to promote ionic conductivity through defect engineering. Initially, defect properties under various growth conditions are investigated to identify optimal conditions for achieving high Na ion conductivity while maintaining low electrical conductivity. Under the Na-rich condition, high concentration of Na_i defect is expected in Na₄OI₂, which facilitates Na ion conductivity; however, the compensation of Na_i and V_Na results in low electrical conductivity, thus avoiding self-discharging. Then, ion-migration simulations reveal a quick migration pathway for the Na_i ion, characterized by an edge of octahedron in the in-plane direction with a dumbbell configuration, with an energy barrier as low as 0.12 eV and a migration rate of 3.6 × 10¹¹ s^-1 at room temperature. Furthermore, the ion conductivity σ for interstitial Na is determined to be 14 mS cm^-1 at RT. This study emphasizes the importance of growth condition control and defect engineering in promoting ion conductivity and overall performance of SSEs and provides creative insights and opportunities for the development of 2D NaAP SSEs.