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The mixed transition-metal layered compound, LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532), is a promising high-energy cathode material. However, the required high-voltage (>4.3 V) cycling is accompanied by a rapid capacity fade associated with a complex redox mechanism that has not been clarified. Here in this paper, we report soft x-ray absorption spectroscopy of NMC532 electrodes, both pristine and those charged to 4.2, 4.35, or 4.5 V in graphite/NMC532 cells. A quantitative sXAS analysis shows that about 20% of the nickel exists as Ni⁴⁺ in the as-synthesized NMC532. The Ni redox reaction contributes only to the experimental capacity obtained below 4.2 V, while Co redoxmore » reactions take place throughout the entire electrochemical cycling up to 4.5 V. In contrast to the changing ratio of the well-defined Ni²⁺, Ni³⁺ and Ni⁴⁺ ions, Co always displays ill-defined intermediate valence states in the charged NMC532 electrodes. This indicates an itinerant electron system in NMC electrodes related to the improved rate performance through Co doping. Furthermore, about 20% of Ni²⁺ is found on the electrode surface at the high potential, which suggests that the electrode surface has either gone through surface reconstruction or reacted with the electrolyte at high voltage.« less