An electrochemical impedance spectroscopic study of the transport properties of LiNi0.75Co0.25O2

Analysis of impedance spectra taken at closely spaced bias potential values on LixNi0.75Co0.25O2 have been interpreted in terms of electronic and ionic transport properties of this electrode material. In the 0.9 < x < I range the material shows semi-conductive properties and the electronic conductivity dominates the transport. For x less than or equal to 0.9, the properties change into those of a metal-like material in which the ionic conductivity becomes the limiting factor. The transition between these two limiting conditions clearly appears in the impedance spectra sequence. This transition is reversible since the same behaviour is observed during the lithium intercalation process as well as in the reverse lithium deintercalation process. (C) 1999 Elsevier Science S.A. All rights reserved.