A New Spinel Chloride Solid Electrolyte with High Ionic Conductivity and Stability for Na-Ion Batteries

Halide materials are of current interest as solid electrolytes for all-solid-state sodium-ion batteries (ASIBs), due to their good balance between ionic conductivity and electrochemical stability. In this work, by using density functional theory combined with deep potential model and grand potential phase diagram analysis, we report a new spinel chloride (Na₂Y_2/3Cl₄) and systemically evaluate its potential for the solid electrolyte. The spinel Na₂Y_2/3Cl₄ exhibits a high ionic conductivity of 0.94 mS/cm at room temperature and has a three-dimensional isotropic diffusion network comprised of face-sharing octahedra and tetrahedra. Further analysis of the diffusion mechanism indicates that the Na⁺ conductivity mainly derives from Na ions in the 8a site while the Na ions in the 16d site are mainly used for forming the rhombus skeleton. Besides, the spinel Na₂Y_2/3Cl₄ has a wide electrochemical window of 0.59-3.76 V and good interfacial stability with high-voltage cathodes, which ensures its ability to improve the energy density of ASIBs. This study demonstrates the promising application of the spinel framework in sodium solid electrolytes and sheds new light on developing the halide-based solid electrolyte for ASIBs.