Cross-length-scale investigation reveals the spatial thermo-chemical dynamics hidden in Ni-rich layered Li-ion cathodes

A long pursuit in developing high-energy batteries is the prognosis and improvement of thermal stability. Here, we report new understandings of the thermo-chemical transformation mechanism of delithiated Ni-rich cathodes at different spatial length scales. Using in situ neutron scattering and pair distribution function analyses, we identify that thermal degradation can be recognized as a topotactic transformation of the oxygen octahedral at angstrom scale. We highlight the importance of building a robust oxygen framework at short range to achieve higher thermal stability. Our in situ spectroscopic nano -tomography resolves the dynamic thermo-chemical interactions inside delithiated particles, illustrating the correlation between thermal performance and spatial distribution of various thermo-chemical interactions. Statistical analyses of thermally active and sluggish regions in cathode particles show that these minority regions (<2% volume fraction) govern thermal stability. We propose effective strategies to manipulate thermo-chemical interaction dynamics and to minimize the propagation of thermally active regions by "flattening the curve."