Battery Systems by Design: Tailoring the Electronic Structure and Cohesive Energy Evolution of the Li ₃ P Solid‐State Electrolyte via Sulfur Doping: A Computational Simulation

In this study, the structural and electronic properties of hexagonal Li ₃ P (space group P6 ₃ /mmc, No. 194) and sulfur‐doped Li ₃ P _{1‐ x} S _x were investigated by the density functional theory (DFT) within the generalized gradient approximation (GGA‐PBE), as implemented in the Quantum ESPRESSO package. After full geometric optimization of the host material, sulfur incorporation was modeled by substituting P atoms within a supercell, corresponding to a 3.125% doping concentration. Cohesive energy analyses confirm the thermodynamic stability of both pristine and doped configurations, as indicated by their negative values. Electronic structure calculations reveal an indirect bandgap of 0.703 eV for pristine Li ₃ P, obtained consistently with both ultrasoft pseudopotential (USPP) and projector augmented‐wave (PAW) PBE functionals. Remarkably, sulfur substitution at P sites induces pronounced reconstruction of the electronic band structure, giving rise to new energy states that cross the Fermi level ( E _F ), which are attributed to the dopant‐induced electronic states. Through systematic structural relaxations and analysis of total (TDOS) and partial (PDOS) densities of states, the underlying modulation mechanism is elucidated. A detailed bonding‐character analysis further identifies the hybridization states of both doped and undoped systems.