Unveiling the potential of Lithium Hexafluorophosphate (LiPF 6 ) as a solid electrolyte material: A first-principles perspective on structural, electronic, and thermal properties

Abstract The growing demand for safer, high-performance energy storage has accelerated the search for efficient solid-state electrolytes (SSEs). A comprehensive first-principles investigation of Lithium Hexafluorophosphate (LiPF6), conventionally used in liquid electrolytes, to assess its potential as a SSE material is reported. Density functional theory (DFT) calculations were employed to examine its structural, electronic, thermal, electrochemical, and Li-ion transport properties. The optimized LiPF6 structure exhibits strong structural and thermodynamic stability, supported by negative cohesive energy and convex-hull analysis. A wide band gap of 7.46 eV indicates excellent electronic insulation, while an electrochemical stability window of 2.73-6.83 V and interfacial stability with different cathode materials highlight its electrochemical compatibility. Thermal analysis shows increasing entropy, stabilized heat capacity, and decreasing free energy at elevated temperatures, indicating good thermodynamic stability. However, Li-ion migration calculations reveal a relatively high diffusion barrier in the range of 0.6 -0.7 eV, suggesting comparable ionic conductivity in pristine LiPF6. These results identify LiPF6 as a structurally, thermally, and electrochemically stable fluoride-based SSE candidate, while emphasizing the need for defect, compositional, or strain engineering to enhance Li-ion transport.