Ductile Na₃La₅Br₁₈ as a Promising Solid-State Electrolyte with Fast Na⁺ Conduction and High Electrochemical and Interfacial Stability

Using density functional theory combined with ab initio molecular dynamics simulation and grand potential phase diagram analysis, we have designed a new sodium bromide solid-state electrolyte Na 3 La 5 Br 18 (NLB) with high dynamical, thermal, mechanical, and thermodynamic stability. It has a large band gap of 4.6 eV and high ductility with a Pugh’s ratio of 2.32. More importantly, this electrolyte exhibits a high ionic conductivity of 9.73 mS/cm at 300 K, a low activation energy of 0.218 eV, a lower migration barrier of 0.16 eV along the crystallographic c -axis, a wide electrochemical window of 0.52–3.70 V, and high chemical interface stability with reported high-potential cathode materials. These findings highlight the potential of NLB as a high-performance solid-state electrolyte for Na-ion batteries and complement the recently synthesized lithium chloride superionic conductor [Yin et al., Nature 2023, 616, 77–83].