Structure and Ionic Conductivity of Li2S–P2S5 Glass Electrolytes Simulated with First-Principles Molecular Dynamics
Frontiers in Energy Research
Lithium thiophosphate-based materials are attractive as solid electrolytes in all-solidstate lithium batteries because glass or glass-ceramic structures of these materials are associated with very high conductivity. In this work, we modeled lithium thiophosphates with amorphous structures and investigated Li + mobilities by using molecular dynamics calculations based on density functional theory (DFT-MD). The structures of xLi 2 S-(100 − x)P 2 S 5 (x = 67, 70, 75, and 80) were created by
... e created by randomly identifying appropriate compositions of Li + , PS 3 4 − , P 4 2 2 S 7 − , and S − and then annealing them with DFT-MD calculations. Calculated relative stabilities of the amorphous structures with x = 67, 70, and 75 to crystals with the same compositions were 0.04, 0.12, and 0.16 kJ/g, respectively. The implication is that these amorphous structures are metastable. There was good agreement between calculated and experimental structure factors determined from X-ray scattering. The differences between the structure factors of amorphous structures were small, except for the first sharp diffraction peak, which was affected by the environment between Li and S atoms. Li + diffusion coefficients obtained from DFT-MD calculations at various temperatures for picosecond simulation times were on the order of 10 −3 -10 −5 Å 2 /ps. Ionic conductivities evaluated by the Nernst-Einstein relationship at 298.15 K were on the order of 10 −5 S/cm. The ionic conductivity of the amorphous structure with x = 75 was the highest among the amorphous structures because there was a balance between the number density and diffusibility of Li + . The simulations also suggested that isolated S atoms suppress Li + migration.