Phase-Transition-Induced\nCrack Formation in LiNi<sub>0.8</sub>Mn<sub>0.1</sub>Co<sub>0.1</sub>O<sub>2</sub> Cathode Materials:\nA Comparative Study of Single-Crystalline and Polycrystalline Morphologie

Nickel-rich layered oxides, particularly LiNi<sub>0.8</sub>Mn<sub>0.1</sub>Co<sub>0.1</sub>O<sub>2</sub> (NMC811), are considered\nsome\nof the most promising candidates for next-generation battery cathode\nmaterials due to their high voltage, high capacity, and cost-effectiveness,\nwhich is attributed to the reduction in the cobalt content. However,\nnickel-rich layered materials suffer from significant capacity decay,\nespecially at high voltages. Therefore, directly observing the crystal\nstructure changes in NMC811 under high voltage and the growth of cracks\nis crucial for understanding the capacity decay mechanism in these\nmaterials. In the present study, we utilized synchrotron radiation\ntechnology to enable real-time tracking of lattice and morphological\nchanges. Specifically, we performed high-resolution X-ray diffraction\non two different forms of NMC811 (single crystalline and polycrystalline)\nunder various delithiation states to analyze their crystal structure\nchanges. Additionally, <i>operando</i> X-ray computed tomography\ntests were conducted to observe the morphological changes during charging\nand discharging.