Sulfur-doped Li1.3Al0.3Ti1.7(PO4)3 as a solid electrolyte for all-solid-state batteries: First-principles calculations

Solid electrolytes are crucial in obtaining high safety standards and high energy densities in all-solid-state bat-teries (ASSBs). For ASSBs, it is essential to design solid electrolytes with high ionic conductivity. Herein, a density functional theory (DFT) study has been conducted to investigate the impact of substitutional sulfur doping into Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte which has a sodium superionic conductor (NaSICON) type crystal structure. A comprehensive study of the effect of sulfur doping on structural stability, Li-ion migration path, and electronic properties was carried out. DFT calculations indicate that sulfur doping locally improves the Li-ion migration kinetics which is accompanied by increased polyhedral volumes in the diffusion path. Moreover, experimental and computational studies were carried out on the electronic state of bare and sulfur-doped LATP. Band gap measurements performed by UV-Vis absorption analysis revealed that sulfur doping decreased the band gap from 2.35 eV to 2.10 eV in alignment with the theoretical calculations in which 1.83 eV was obtained in the most stable sulfur-doped configuration. Compared with bare-LATP, it has been validated that S@LATP has better ionic conductivity with reducing activation energy barrier as a solid electrolyte for all-solid-state batteries.