Novel Solid-State Electrolyte Na₃La₅Cl₁₈ with High Stability and Fast Ionic Conduction

Motivated by the recent experimental synthesis of a LaCl₃-based lithium superionic conductor [Yin, Y.-C.Nature 2023, 616, 77–83], we explore the potential of a LaCl₃-based system for a sodium superionic conductor in this work. Using density functional theory combined with molecular dynamics simulation and a grand potential phase diagram analysis, we find that the resulting Na₃La₅Cl₁₈ exhibits high energetic stability with a small energy-above-hull of 18 meV per atom, a large band gap of 5.58 eV, a wide electrochemical window of 0.41–3.76 V from the cathodic to the anodic limit, and a high Na⁺ conductivity of 1.3 mS/cm at 300 K. Furthermore, Na₃La₅Cl₁₈ shows high chemical interface stability with the reported high-potential cathode materials such as NaCoO₂, NaCrO₂, Na₂FePO₄F, Na₃V₂(PO₄)₃, and Na₃V₂(PO₄)₂F₃. These findings clearly suggest that the LaCl₃-based framework can be used as a building block not only for Li-ion but also for Na-ion batteries.