Effect of iron on the electrochemical behaviour of lithium nickelate:: from LiNiO2 to 2D-LiFeO2

Iron substituted lithium nickelate have been obtained by high temperature solid 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 show that, in normal synthesis conditions, the amount of 3d cations in the Lithium 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 cationic 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 lithium plane in good agreement with the result previously reported by Reimers and Dahn [1]. The electrochemical behaviour of these materials has been studied in lithium batteries. The reversible capacity is small vs. unsubstituted phases, A Mossbauer spectroscopy study has shown that iron and nickel are simultaneously oxidised upon lithium deintercalation. The electrochemical behaviour of these materials has been compared to that of layered LiFeO2 and NaFeO2. (C) 2000 Elsevier Science B.V. All rights reserved.