Grain Boundaries and Their Impact on Li Kinetics in Layered-Oxide Cathodes for Li-Ion Batteries

Defects are pervasive in electrochemical systems across multiple length scales. The defect chemistry largely differs from the bulk behavior and often dictates the rate performance for battery materials. However, the impact of material defects on Li kinetics remains elusive because of their complex nature and the sensitivity of the reaction kinetics on the local atomic environment. Here we focus on the grain boundaries (GBs) in layered-oxide cathodes and address their role in Li transport using the firstprinciples theoretical approach. We construct the coincidence site lattices of Sigma 2(1 (1) over bar0 (4) over bar), Sigma 3((1) over bar 10 (2) over bar), Sigma 5(1 (1) over bar0 (1) over bar), and Sigma 9((1) over bar 10 (4) over bar) GBs. The energy profiles for Li migration across and along the grain planes are plotted. We discuss in detail how the atomistic features associated with various grain structures such as the local structural distortion and charge redistribution determine the Li transport kinetics. Specifically, the coherent Sigma 2 GBs facilitate Li migration with 1-2 orders of magnitude increased diffusivity than the bulk diffusion, the asymmetric Sigma 3 GBs significantly impede Li diffusion, and the locally disordered Sigma 5 and Sigma 9 GBs cause slightly increased Li diffusivity at the intermediate diffusion distance (similar to 15 A). We further evaluate the overall Li diffusivity and conductivity in the layered-oxide lattice by a distinction of Li transport in the bulk, across the GBs, and along the grain planes. The fundamental understanding sheds insight on a prevalent defect in the state-of-the-art cathode and its potential optimization of Li kinetics.

Automated summary

This study focuses on the role of grain boundaries in layered-oxide cathodes in Li transport, using first-principles theoretical approach to investigate the impact of different grain boundary structures on Li transport kinetics. Results show that some grain boundaries facilitate Li migration, while others significantly impede Li diffusion, leading to varying effects on Li diffusivity.