Annealing-Induced Dynamic Strain Evolution in Cycled High-Ni Layered Oxides Revealing Latent Lattice Imperfections

High-Ni layered oxides undergo distinct chemomechanical evolution upon high-voltage charging over 4.2 V, producing crystallographic defects and associated lattice distortions within the cathode particles. Due to the significant recovery of chemomechanical evolutions during discharging, lattice imperfections resulting from high-voltage charging tend to remain hidden and pose challenges in their characterization at discharged states. Moreover, their impact on the structural stability and electrochemical performance of cathode materials remains elusive. In this study, synchrotron-based X-ray diffraction and Bragg coherent diffraction imaging (CDI) successfully detects subtle yet persistent lattice distortions in the discharged state after high-voltage cycling. In situ Bragg CDI further reveals internal strain evolution within the particles upon mild heating, which can be correlated with hidden lattice imperfections and structural instability. Despite comparable strain distributions before heating, the particles cycled over 4.2 V show significant strain evolution and intraparticle domain deformation upon heating, whereas the particles cycled below 4.2 V release the internal strain and retain their shape. These results suggest that latent lattice imperfections formed during high-voltage cycling can trigger detrimental microstructural degradation at high temperatures and critically deteriorate the structural stability of the high-Ni layered oxide particles, thereby increasing the potential risk of degradation at elevated temperatures.

Automated summary

High-Ni layered oxides undergo chemomechanical evolution during high-voltage charging, leading to crystallographic defects and lattice distortions within cathode particles. However, these lattice imperfections are difficult to characterize in discharged states due to the significant recovery during discharging. This study successfully detects subtle yet persistent lattice distortions in the discharged state using synchrotron-based X-ray diffraction and Bragg coherent diffraction imaging.