We studied the electronic structure of the transition metal ions in deintercalated and reintercalated LiCo0.5Ni0.5O2 The experimental technique used in the study was Co 2p and Ni 2p X-ray absorption spectroscopy. The shapes of the multiplet in the spectra are directly related to the ground state of the transition metal ions. The experimental results were analyzed using atomic multiplet plus crystal field calculations. The Co ions were in a trivalent Co3+ low-spin state in LiCo0.5Ni0.5O2 and remained mostly unaffected by Li deintercalation down to x = 0.20, The Ni ions were in a divalent Ni2+ high-spin state in LiCo0.5Ni0.5O2 and not in the usually quoted trivalent Ni3+ state. The Ni ions were partially oxidized to a trivalent Ni3+ state upon Li deintercalation down to x = 0.50. Further Li deintercalation, down to x = 0.20, did not result in further oxidation of the Ni ions. The changes in the electronic structure of the Ni ions were reversible upon Li reintercalation.