Electronic structure of the transition metal ions in LiCoO 2, LiNiO 2 and LiCo 0.5Ni 0.5O 2

Abstract

We studied the electronic structure of the transition metal ions in LiCoO 2, LiNiO 2 and LiCo 0.5Ni 0.5O 2. The experimental technique used in the study was Co 2p and Ni 2p X-ray absorption spectroscopy. The experimental results were analyzed using atomic multiplet plus crystal field calculations. The Co ions in LiCo 0.5Ni 0.5O 2 are in a trivalent Co 3+ low-spin state given by t 2g 6 ( 1A 1 ), as in LiCoO 2. The Ni ions in LiCo 0.5Ni 0.5O 2 are in a divalent Ni 2+ high-spin state given by t 2g 6e g 2 ( 3 A 2 ), as in LiNiO 2. The missing charge at the Ni site is compensated by a less negative O ion; this means that the charge state in LiNiO 2, for instance, is closer to Li +Ni 2+O 2 1.5− than to the usually quoted Li +Ni 3+O 2 2−. This is important for understanding the oxidation–reduction processes upon Li deintercalation–reintercalation reactions.