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

Abstract

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 ∑2(11̅ 04̅ ), ∑3(1̅ 102̅ ), ∑5(11̅ 01̅ ), and ∑9(1̅ 104̅ ) 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 ∑2 GBs facilitate Li migration with 1−2 orders of magnitude increased diffusivity than the bulk diffusion, the asymmetric ∑3 GBs significantly impede Li diffusion, and the locally disordered ∑5 and ∑9 GBs cause slightly increased Li diffusivity at the intermediate diffusion distance (∼15 Å). 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.

Review on the lithium transport mechanism in solid‐state battery materials

“…It is generally considered that the diffusion along interfaces is faster than that across interfaces, which has been demonstrated in SE Li 3 OCl 98 and cathode material LiNi 0.5 Mn 0.3 Co 0.2 O 2 . 99…”

Chemomechanics of Rechargeable Batteries: Status, Theories, and Perspectives

“…Grain boundaries, including antiphase boundaries and twin boundaries, regulate the phase transformation process . Although experimentally investigating the grain boundaries can be challenging, prior computational works suggest that grain boundaries can hinder diffusion. − The mismatched volume change in different grains leads to crack formation along grain boundaries. , …”

Hydration of LiOH and LiCl─Near-Infrared Spectroscopic Analysis

“…Furthermore, rechargeable batteries have been widely studied as carbon-neutral energy sources. In particular, all-solid-state lithium ion batteries, wherein flammable organic electrolytes are replaced with non-flammable inorganic electrolytes, have received much attention for reducing CO 2 emissions. − In this system, various sulfide-based solid electrolytes, for example, Li 2 S–P 2 S 5 glass ceramics and hali-chalcogenide Li 6 PS 5 Cl (argyrodite phase) exhibited ultrahigh Li + ion conductivity and a wide electrochemical window. − ,− Sulfide-based solid electrolytes show high chemical stability in a low humidity atmosphere, indicating that the materials should be administrated under dry air or inert gas flow conditions. However, sulfide-based materials hydrolyze with water in air to generate H 2 S gas .…”