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

Motivated by the recent experimental synthesis of a LaCl 3 -based lithium superionic conductor [ Yin, Y.-C. Nature 2023, 616, 77–83], we explore the potential of a LaCl 3 -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 Na 3 La 5 Cl 18 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, Na 3 La 5 Cl 18 shows high chemical interface stability with the reported high-potential cathode materials such as NaCoO 2, NaCrO 2, Na 2 FePO 4 F, Na 3 V 2 (PO 4 ) 3, and Na 3 V 2 (PO 4 ) 2 F 3 . These findings clearly suggest that the LaCl 3 -based framework can be used as a building block not only for Li-ion but also for Na-ion batteries.