Electronic Structure of Transition Metal Ions in Deintercalated and Reintercalated LiCo[sub 0.5]Ni[sub 0.5]O[sub 2]

We studied the electronic structure of the transition metal ions in deintercalated and reintercalated LiCo 0.5 Ni 0.5 O 2 . 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 Co 3 + low‐spin state in LiCo 0.5 Ni 0.5 O 2 and remained mostly unaffected by Li deintercalation down to x = 0.20. The Ni ions were in a divalent Ni 2 + high‐spin state in LiCo 0.5 Ni 0.5 O 2 and not in the usually quoted trivalent Ni 3 + state. The Ni ions were partially oxidized to a trivalent Ni 3 + 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.