context: High energy density lithium ion batteries have been applied as the main energy storage technology in portable devices and green transportation. LiCoO2, a layered oxide cathode in lithium ion batteries, has obtained unprecedented success since its commercialization in the 1990s. LiNiO2, isostructural to LiCoO2, can deliver a higher capacity within a relatively low upper cutoff voltage. However, its practical application has been hindered due to the inherent structural instability. Thus, cobalt, as an essential element, has been incorporated into the LiNiO2 system to form LiNi1−x−yMnyCoxO2 (NMC) and LiNi1−x−yCoxAlyO2 (NCA) materials to release the strong magnetic moment and ultimately stabilize the structure. At present, researchers are pursuing the theoretical capacity of NMCs either by elevating the high cutoff voltage or increasing the nickel concentration. However, these strategies have inevitably provoked some of the degradation pathways of these materials, including transition metal reduction/dissolution, surface reconstruction, gas evolution, electrolyte oxidation/decomposition, and chemomechanical breakdown. Additionally, most of these materials are synthesized in the polycrystalline form and have heterogeneous chemistry, resulting in high heterogeneous degradation patterns.
answer: LiCoO2