Abstract
Looking for solid state electrolytes with fast lithium ion conduction is an important prerequisite for developing all-solid-state lithium secondary batteries. By combining the simulation techniques in different levels of accuracy, e.g. the bond-valence (BV) method and the density functional theory (DFT), a high-throughput design and optimization scheme is proposed for searching fast lithium ion conductors as candidate solid state electrolytes for lithium rechargeable batteries. The screening from more than 1000 compounds is performed through BV-based method, and the ability to predict reliable tendency of the Li+ migration energy barriers is confirmed by comparing with the results from DFT calculations. β-Li3PS4 is taken as a model system to demonstrate the application of this combination method in optimizing properties of solid electrolytes. By employing the high-throughput DFT simulations to more than 200 structures of the doping derivatives of β-Li3PS4, the effects of doping on the ionic conductivities in this material are predicted by the BV calculations. The O-doping scheme is proposed as a promising way to improve the kinetic properties of this materials, and the validity of the optimization is proved by the first-principles molecular dynamics (FPMD) simulations.
Highlights
The approaches to understand ionic migration in solids start with space topology determined by the net channels in a specific crystalline structure[10,11]
The critical isovalue to form a continuous channel in a certain direction reflects the migration energy barrier in this path, and the narrowest position along this way corresponds to the maximum energy image along this migration path, namely, the saddle point energy associated with a transition state
Previous density function theory (DFT) investigations reveal that the lithium layer is the main diffusion plane in this material, while the Li ions in the transition-metal layer can diffuse in the structure by migrating into the lithium layer firstly[34]
Summary
The approaches to understand ionic migration in solids start with space topology determined by the net channels in a specific crystalline structure[10,11] This method is based on the hard geometric constrains in the atomic sublattice, from which a map of void, channel, and migration path is obtained by using the model of excluded volume and Voronoi-Dirichlet partition[11,12,13]. The calculated energy barriers with higher reliability can be obtained from the transition-state method or the molecular dynamics method based on density function theory (DFT)[7,8,26] They suffer from high computation cost which limits their efficiency on screening of materials based on ionic transport properties. An optimization scheme is proposed for this material
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