High energy nickel-rich NMC (LiNi_xMn_yCo_zO₂; x+y+z≈1, x≥y+z) cathodes offer promising theoretical high capacity cell metrics. As the nickel content increases, the cathode exhibits a decrease in capacity retention, structural stability, and thermal stability. Herein, the thermal stability of chemically delithiated NMC-811 is investigated as a function of lithium content. A myriad of synchrotron characterization techniques are used to understand the role of the transition metals on structure stability at elevated temperatures. The in-situ heating experiments capture both chemical and morphological changes within the material that yield key particle size information on thermal stability. The bulk and surface sensitive techniques capture intermediate states between the transition metal 3d-oxygen 2p bonds at low temperatures, which inevitably can lead structural changes. This work demonstrates the importance in developing robust cathode materials for lithium ion batteries.