Nanomechanical characterization and mechanical integrity of unaged and aged Li-ion battery cathodes

• Nanomechanical and mechanical integrity tests conducted on Li-ion battery cathodes.
• The aged cathode showed higher hardness, creep depth and critical load in scratch.
• The aged cathode shows lower wear depth and coefficient of friction.
• The aged cathode showed high creep behavior, suggesting PVDF binder degradation.
• High hardness in the aged cathode, believed to make it brittle, seen in scratch test.

Lithium-ion (Li-ion) batteries have been implemented for numerous applications, one of which is in plug-in hybrid electric vehicles (PHEV) and pure electric vehicles (EV). In an effort to prolong battery life it is important to understand the mechanisms that cause reduced battery capacity with aging. In this work, nanomechanical characterization and mechanical integrity studies were carried out on unaged and aged LiFePO4 battery cathodes using atomic force microscopy (AFM) and nanoindentation. Changes in hardness, elastic modulus, creep, nanowear, nanoscratch and nanofriction properties were measured. Measured changes are believed to occur as a result of coarsening and agglomeration of LiFePO4 nanoparticles.

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