Calcination Heterogeneity in Ni-Rich Layered Cathodes Drives Chemo-Mechanical Failure

Ni-rich layered oxide cathode materials are at the forefront of high-energy density Li-ion battery cathodes, due to their high energy densities. However, these materials suffer from severe degradation in the form of capacity loss. The commonly understood origin for the degradation is from the formation and propagation of microcracks within the spherical, polycrystalline morphology due to deep delithiation, referred to as chemo-mechanical failure. Addressing this chemo-mechanical degradation is essential to encourage widespread adoption of such cathodes in portable energy storage applications, such as EVs.
Current approaches to address the degradation of Ni-rich cathodes involve electrolyte engineering or surface coating to improve interfacial stability, doping the bulk with high-valent dopants to alter the microstructure, or nanostructuring precursors with carefully controlled morphologies. While these approaches are often successful in reducing the observed degradation, they often rely on expensive and complicated processing.
In this work, we use a combination of in-situ and ex-situ microscopy tools to identify the origin of chemo-mechanical failure in Ni-rich layered oxides. Heterogeneity between primary and secondary particles is found to drive cracking and chemo-mechanical failure, and we delineate the mechanism using structural, spectroscopic and microscopy tools. We also evaluate the efficacy and working mechanism behind several microstructure modification tools using our toolkit and identify promising routes to mitigate chemo-mechanical failure and extend the lifetime of Co-free and Ni-rich, high energy density cathode materials.