In situ structural and electrochemical study of Ni1-xCoxO2 metastable oxides prepared by soft chemistry

Metastable Ni1-xCoxO2 phases were obtained from the electrochemical deinter calation of lithium from the precursor phases, LiNi1-xCoxO2 (x = 0, 0.3, an d 1), using plastic electrochemical cells, The structural changes induced d uring Li removal, together with the thermal stability of the end members Ni 1-xCoxO2, were determined by in situ X-ray measurements using a high-resolu tion synchrotron beam line, The advantages of using a plastic battery confi guration to perform such a study is emphasized. The structural/thermal stab ility results are discussed in relation to the electrochemical performance of these materials. Numerous changes in the unit cell symmetry were observe d during deintercalation, The NiO2 end member is described with a single di storted CdI2-type structure, while two CdI2-type structures, both with redu ced O-O interlayer distances, but differing by the presence of oxygen vacan cies, are needed to describe the CoO2 end member. The reduction in O-O spac ing is explained by partial polymerization within oxide frameworks. Such a behavior, already observed with layered chalcogenides, can be explained on the basis of the elegant electron-hole chemistry pioneered by J. Rouxel who directly evidenced the role of the anion during an intercalation process. (C) 1999 Academic Press.