In Situ Structural and Electrochemical Study of Ni1−xCoxO2 Metastable Oxides Prepared by Soft Chemistry

Abstract Metastable Ni 1− x Co x O 2 phases were obtained from the electrochemical deintercalation of lithium from the precursor phases, LiNi 1− x Co x O 2 ( x =0, 0.3, and 1), using plastic electrochemical cells. The structural changes induced during Li removal, together with the thermal stability of the end members Ni 1− x Co x O 2 , were determined by in situ X-ray measurements using a high-resolution synchrotron beam line. The advantages of using a plastic battery configuration to perform such a study is emphasized. The structural/thermal stability results are discussed in relation to the electrochemical performance of these materials. Numerous changes in the unit cell symmetry were observed during deintercalation. The NiO 2 end member is described with a single distorted CdI 2 -type structure, while two CdI 2 -type structures, both with reduced O–O interlayer distances, but differing by the presence of oxygen vacancies, are needed to describe the CoO 2 end member. The reduction in O–O spacing 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.