# Computational Analysis of Composition-Structure-Property-Relationships in NZP-type Materials for Li-Ion Batteries

## TL;DR

This study uses density functional theory to systematically analyze how composition and structure influence lithium ion migration in NZP-type materials, challenging previous assumptions about migration barriers.

## Contribution

It provides new insights into the relationship between ionic neighborhood and activation energies in NZP compounds, improving understanding of their suitability for solid electrolytes.

## Key findings

- Ionic radii influence structural features and activation energies.
- Structural bottlenecks are not the primary factor for migration barriers.
- Ionic neighborhood around Li ions determines migration activation energies.

## Abstract

Compounds crystallizing in the structure of NaZr$_2$(PO$_4$)$_3$ (NZP) are considered as promising materials for solid state electrolytes in Li-ion batteries. Using density functional theory (DFT), a systematic computational screening of 18 NZP compounds, namely LiX$_2$(LO$_4$)$_3$ with X = Ti, V, Fe, Zr, Nb, Ru, Hf, Ta, Os, and L = P, Mn is performed with respect to their activation energies for vacancy-mediated Li migration. It is shown how the different ionic radii of the cationic substitutions influence structural characteristics such as the octahedron volumes around Li ions on the initial and transition state sites, which affect the activation energies (''composition-structure-property'' relationships). The prevalent assumption that structural bottlenecks formed by triangularly arranged oxygen atoms at a certain location along the migration path determine the energy barriers for Li migration is not supported by the DFT results. Instead, the ionic neighborhood of the migrating ion in the initial and in the transition state needs to be taken into account to relate the structure to the activation energies. This conclusion applies to Na containing NZP compounds as well.