Revealing two distinctive intergranular cracking mechanisms of Ni-rich layered cathode by cross-sectional scanning electron microscopy

Thorough understanding of intergranular cracking mechanism is essential and important for developing superior layered cathodes. As a chemomechanical failure, crack's nucleation and evolution are affected mainly by cycling protocols, but it is still lacking direct and accurate observations. Herein, we develop an experimental protocol to visualize the cracking evolution process by tracing the same secondary particles. Further combining large area cross-sectional observations, we identify two distinctive cracking mechanisms due to different state of charge (SOC). At low SOC, chronic fatigue cracking is dominant. At high SOC, particle bursting makes intergranular cracks quickly saturated during the initial cycles, causing battery rapid performance decay in the beginning. We further validate that cracks are nucleated at the end of charging process and it is the discharging that leads to high density of cracks. Managing individual secondary particle below the critical SOC to prevent particle bursting is essential for achieving high cycling stability of Ni-rich layered cathodes.

Automated summary

The research found that chronic fatigue cracking dominates at low SOC, while particle bursting causes rapid saturation at high SOC. Managing individual secondary particles to prevent bursting is crucial for achieving high cycling stability of Ni-rich layered cathodes.