New publication: Understanding cracks in NMC811 battery particles

In their latest publication on "Impact of grain orientation architecture and boundary properties on chemo-mechanical cracking in NMC811 particles" the DigiCell team at Johannes Kepler University Linz investigates why NMC811 cathode particles crack during battery operation. NMC811 is a nickel-rich material that can store a large amount of energy, but repeated charging and discharging can cause it to fracture and reduce battery lifetime.

The researchers developed a fully coupled phase-field model that links lithium transport, mechanical stress and crack formation. The model represents NMC811 particles as collections of differently oriented primary crystals and includes variations in grain-boundary strength caused by manufacturing defects. It reproduces both cracks between grains and cracks through individual grains, in agreement with experimental observations. The simulations show that larger differences in crystal orientation create greater stress at grain boundaries and accelerate crack formation. Higher charging and discharging rates also increase lithium concentration gradients and promote mixed fracture. Once cracks form, they disrupt lithium transport, change the open-circuit voltage more rapidly and reduce the amount of lithium that can be used. The study further shows that particle architecture matters. A structure with low-misorientation grains near the surface and higher-misorientation grains towards the centre can limit surface crack formation and confine damage. Stronger and more uniform grain boundaries also reduce crack density and prevent cracks from spreading through the particle.

These findings provide guidance for designing more durable NMC811 cathodes. Improving grain-boundary strength, controlling crystal orientation and avoiding excessively high charging rates could help reduce particle damage and extend battery cycle life.

Read the full publication