Kinetics of Li transport in vanadium-based disordered rocksalt structures

TL;DR

This study investigates lithium-ion transport in disordered rocksalt cathodes, revealing how site occupancy and correlated motion influence diffusion, with implications for improving battery performance.

Contribution

It provides new insights into Li+ transport mechanisms in DRX materials using first-principles and kinetic simulations, emphasizing the role of site occupancy and energy distribution.

Findings

Both tetrahedral and octahedral Li sites are crucial for accurate transport prediction.

Li+ diffusion varies with Li content due to site stability and percolation network changes.

Correlated Li+ motion, caused by wide energy distributions, hinders transport.

Abstract

Disordered rocksalt Li-excess (DRX) compounds have emerged as promising new cathode materials for lithium-ion batteries, as they can consist solely of resource-abundant metals and eliminate the need for cobalt or nickel. A deeper understanding of the lithium-ion transport kinetics in DRX compounds is essential for enhancing their rate performance. This study employs first-principles calculations, cluster expansion techniques, and kinetic Monte Carlo simulations to investigate the Li+ transport properties in DRX Li2-xVO3, where 0 <= x <= 1. Our findings underscore (i) the necessity of accounting for both tetrahedral and octahedral Li occupancy when predicting the transport properties in DRX materials, (ii) the factors influencing the variation in the diffusion coefficients with Li content in Li2-xVO3, and (iii) the impact of Li+ correlated motion on the kinetics of Li+ transport. We reveal that the relative stability of tetrahedral and octahedral Li determines the number of active sites within the percolation network, subsequently affecting the Li+ transport properties. Furthermore, we demonstrate that the wide site-energy distribution causes correlated motion in Li2-xVO3, which hinders Li+ transport. Although our study focuses on Li2-xVO3 as a model system, the insights gained apply to all DRX materials, given their inherently broader site-energy distributions.