Theoretical study on stability and ion transport property with halide doping of Na3SbS4 electrolyte for all-solid-state batteries

Abstract

All-solid-state Na ion battery (ASS-NIB) is a new class of battery which is a potential alternative to the conventional all-solid-state Li ion battery. Herein, we focused on Na3SbS4, a reported candidate solid electrolyte for ASS-NIB application, and performed a comprehensive theoretical study, primarily based on density functional theory calculations, to evaluate (electro)chemical stability, defect chemistry, and Na ion transport property. The calculated results reveal that when in contact with a layered cathode compound (e.g., NaCrO2), sulfur in Na3SbS4 tends to migrate across the interface, leading to interface atomic rearrangement, interface disordering and/or decomposition. The material is also predicted to decompose under reductive voltage conditions (0 V vs. Na+/Na), in agreement with experiment. Kinetic modeling for stresses and electron density distribution showed that the interface between Na3SbS4 and Na metal anode under typical electrodeposition surface roughness would lead to dendrite initiation and growth. Aside from controlling Na vacancy concentration, halide doping at the S site was predicted by DFT molecular dynamics (MD) calculations to directly affect the Na+ ion activation energy. This can be ascribed to the size modulation of the Na site-to-site pathway bottleneck. Cl and Br halide dopants are both determined to be promising for conductivity optimization, with low DFT-MD Na+ ion activation energy (∼0.1 eV at 4% Na vacancy). Thermodynamic analysis shows the possible factors that can influence the final conductivity of Na3SbS4: secondary phases and intrinsic defects. Overall, our findings offer valuable insights for the rational design of solid electrolytes.