Electro-chemo-mechanical behavior of a layered cathode material upon cycling

Abstract

The mechanical characteristics of lithium-ion cathode materials plays a critical role in determining battery performance such as durability, cycle life, and safety, especially when the battery is under external pressure which is typical for all-solid-state batteries. This study focuses on LiCoO₂ (LCO), a widely used hexagonal layer-structured cathode material for lithium-ion batteries, and investigates its mechanical properties during de-/lithiation using sputter-deposited thin films and nanoindentation. The values of the experimental Young’s modulus in pure (101) and (003) lattice orientations are quantified to 337.1 $\pm$ 8.7 GPa and 267.9 $\pm$ 7.2 GPa, respectively, in the fully lithiated state. Furthermore, a substantial texture-dependent decrease in Young’s modulus upon lithium deintercalation is demonstrated, probably due to modification of the bonding interactions between the cobalt oxide layers. The decrease of Li content also elevates the relative contribution of plastic deformation, indicating that dislocation glide becomes easier in deintercalated states. By extensive cycling, the Young’s modulus in higher lithiated charge-states decreases considerably which is most-likely due to irreversibility of phase transitions. In contrast, the material shows a significant increase of plastic hardness with cycling, understood as work hardening. The work provides valuable insight on the dynamic changes of the mechanical properties during electrochemical cycling of LiCoO₂, which paves the way for all other layered cathode materials.