A new universal force-field for the Li2S–P2S5 system

Lithium thiophosphate electrolyte is a promising material for application in all-solid-state batteries. Ab initio molecular dynamics (AIMD) simulations have been used to investigate the ion conduction mechanisms in single-crystalline and glassy compounds. However, the complexity of real materials (e.g., materials with grain boundaries and multiphase glass-ceramics) causes AIMD simulations to have high computational cost. To overcome this computational limitation, we developed a new interatomic potential for classical molecular dynamics (CMD) simulations of Li solid-state electrolytes. The training datasets were generated from representative sulfide electrolytes (β-Li3PS4, γ-Li3PS4, Li4P2S6, Li7P3S11, and Li7PS6 crystals and 70Li2S–30P2S5 glass). Using the functional forms of the Class II and Stillinger–Weber potentials, all parameters were optimized by minimizing the differences in forces on atoms, stresses, and potential energies between the CMD and AIMD results. Subsequent validation showed that the optimized parameters can reproduce the dynamics of Li+ as well as the structures of the crystalline and glassy materials. The ionic conductivity of Li7P3S11 crystal was approximately five times that of the isostoichiometric 70Li2S–30P2S5 glass, indicating that CMD simulations using the developed force-field accurately reproduced the effective conduction path in Li7P3S11 from AIMD. The developed force-field parameters make it possible to simulate complex materials including amorphous–crystalline interfaces and multiphase glass-ceramics in the CMD framework.