Computational Analysis of Li Diffusion in NZP-Type Materials by Atomistic Simulation and Compositional Screening

Solid state electrolytes (SSEs) can become a key component for the development of novel reliable, safe, and highly efficient Li-ion batteries. This work focuses on the vacancy-mediated diffusion of Li ions through solid compounds with NZP crystal structures [e.g. LiTi₂(PO₄)₃ (LTP); NZP stands for NaZr₂(PO₄)₃], which is a promising class of materials for the application as SSEs. Since this crystal structure is known to be stable for many combinations of elements on the cation positions, the activation energies for vacancy jumps were calculated in this work for a variety of NZP-type compounds with different compositions. First-principles calculations based on density functional theory were performed to determine the migration barrier heights, and to correlate their values to structural characteristics. In addition, the bond valence method was applied to the NZP-type compounds, which not only helps to identify diffusion networks and transition points, but which can also be valuable for predicting qualitative trends by systematic compositional screening.