Why single-crystal EV batteries crack, fade, and sometimes fail

Researchers from Argonne National Laboratory and the University of Chicago have uncovered the underlying cause of degradation in single-crystal nickel-rich lithium-ion cathodes used in electric vehicle (EV) batteries. While single-crystal cathodes were initially expected to outperform traditional polycrystalline cathodes by avoiding grain boundary-related cracking, they still exhibited unexpected cracking and performance fade. Using advanced synchrotron X-ray and electron microscopy techniques, the team discovered that reaction heterogeneity within single-crystal particles causes internal strain, leading to nanoscale fractures from within the particles, a degradation mechanism distinct from that in polycrystalline materials. This insight challenges previous assumptions and conventional design principles that were based on polycrystalline cathodes. Notably, the study found that cobalt, which in polycrystalline cathodes tends to promote cracking but prevents structural disorder, actually improves durability in single-crystal cathodes, whereas manganese causes more mechanical damage. These findings suggest that new design strategies and material compositions are necessary to enhance battery longevity and safety.