Changes in the electronic structure of chemically deintercalated LiCoO2

We studied the changes in the electronic structure of LiCoO2 induced by Li deintercalation using Co 2p and O 1s X-ray absorption spectroscopy. The mean probing depth of this technique is similar to 50 Angstrom. The results were analyzed using atomic multiplet and band structure calculations. The Co 2p spectrum shows that the Co ions in LiCoO2 are in a trivalent Co3+ low-spin state. The Co 2p spectra of deintercalated LiCoO2 show only minor changes as a function of Li concentration. The absence of changes indicates that the Co ions remain mostly unaffected by Li deintercalation. In particular, the Co ions in deintercalated LiCoO2 are not oxidized to a tetravalent Co4+ state as normally assumed. The O 1s spectra of deintercalated LiCoO2 show an increase in the absorption intensity below threshold; this absorption increase indicates that the O ions in LixCoO2 are reduced upon Li deintercalation. (C) 2000 The Electrochemical Society. S1099-0062(00)05-077-X. All rights reserved.