There is an increasing interest in studying the high Ni-content layered oxide materials for Li-ion batteries, especially for their application in electrical vehicles, since they are promising candidates for next-generation energy storage materials. Compared to traditional layered oxide materials such as LiCoO₂ (LCO) or LiNi_1/3Mn_1/3Co_1/3 O₂ (NMC333), high Ni-content materials can provide higher specific capacity and energy density due to the two electron transfer per Ni by the Ni²⁺/Ni⁴⁺ redox couple. However, these materials are still suffering from the problems of capacity fading. It is quite important to understand the relationship between performance deterioration and structural degradation. The in-depth understanding of such relation can provide valuable guidance for future material design. The results obtained from our newly developed multi-scale characterization techniques will be reported, including the state-of-the-art aberration-corrected scanning transmission microscopy (STEM) imaging, STEM-electron energy loss spectroscopy (EELS), X-ray imaging, X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS). These results show that such multi-scale combined characterization tools can help us to study the formation of internal nano-pore structure at primary particle level and understand its impact on the formation of micro-cracks at secondary particle level. This structure degradation is highly correlated to the irreversible cation migration and intermixing at atomic level during extensive electrochemical cycling. Also, we found that the surface plays a vital role in the function of these materials. By combining the synchrotron based X-ray techniques with electron microscopy and spectroscopy, this presentation will report the degradation pathway of high Ni-content cathode materials for Li-ion batteries.