Effect of iron on the electrochemical behaviour of lithium nickelate: fromLiNiO2 to 2D-LiFeO2

Iron substituted lithium nickelate have been obtained by high temperature s olid state chemistry. The general formula deduced from structural analysis is Li1-z(Ni1-yFey)(1+z)O-2. Layered phases are obtained for y less than or equal to0.30. The Rietveld refinements of the X-ray diffraction patterns sh ow that, in normal synthesis conditions, the amount of 3d cations in the Li thium plane ranges between 0.06 and 0.08. The neutron diffraction study of a material which contains a large amount of extra-cations (z = 0.14) shows that there is no lithium ions in the nickel plane; i.e. there is no cationi c mixing. The comparative Mossbauer study of lithium phases with homologous strict 2D sodium phases shows that a small amount of iron ions is in the l ithium plane in good agreement with the result previously reported by Reime rs and Dahn [1]. The electrochemical behaviour of these materials has been studied in lithium batteries. The reversible capacity is small vs. unsubsti tuted phases, A Mossbauer spectroscopy study has shown that iron and nickel are simultaneously oxidised upon lithium deintercalation. The electrochemi cal behaviour of these materials has been compared to that of layered LiFeO 2 and NaFeO2. (C) 2000 Elsevier Science B.V. All rights reserved.