Determining the Fundamental Failure Modes in Ni-rich Lithium Ion Battery Cathodes

TL;DR

This study investigates the mechanical failure mechanisms in Ni-rich lithium-ion battery cathodes, revealing dislocation slip systems and their role in crack formation through in situ micromechanical testing, aiding in improved material design.

Contribution

It provides the first direct measurement of local mechanical properties and dislocation slip systems in single crystal Ni-rich cathodes, clarifying failure mechanisms.

Findings

Dislocation slip systems identified in Ni-rich cathodes.

Slip facilitates crack initiation and propagation.

Comparison of single crystal and polycrystal deformation behaviors.

Abstract

Challenges associated with in-service mechanical degradation of Li-ion battery cathodes has prompted a transition from polycrystalline to single crystal cathode materials. Whilst for single crystal materials, dislocation-assisted crack formation is assumed to be the dominating failure mechanism throughout battery life, there is little direct information about their mechanical behaviour, and mechanistic understanding remains elusive. Here, we demonstrated, using in situ micromechanical testing, direct measurement of local mechanical properties within LiNi0.8Mn0.1Co0.1O2 single crystalline domains. We elucidated the dislocation slip systems, their critical stresses, and how slip facilitate cracking. We then compared single crystal and polycrystal deformation behaviour. Our findings answer two fundamental questions critical to understanding cathode degradation: What dislocation slip systems operate in Ni-rich cathode materials? And how does slip cause fracture? This knowledge unlocks our ability to develop tools for lifetime prediction and failure risk assessment, as well as in designing novel cathode materials with increased toughness in-service.