Electrochemical behavior of iron-substituted lithium nickelate

Lamellar phases with nominal composition Li(Ni1-yFey)O-2 (y less than or equal to 0.30) were synthesized and characterized by Rietveld refinement of their X-ray diffraction (XRD) patterns. These materials exhibited the formula Li1-z(Ni1-yFey)(1+z)O-2 with 0.06 less than or equal to z less than or equal to 0.08 and were used as positive electrodes in lithium batteries. Their electrochemical performances decreased with increasing iron content. The Li-x(Ni0.90Fe0.10)(1.06)O-2 phases were characterized by XRD and Mossbauer spectroscopy. A solid solution appeared in the entire deintercalation domain 0.28 less than or equal to x less than or equal to 0.94, and Rietveld refinement of the XRD patterns allowed us to characterize the variation of structural parameters upon lithium deintercalation. Fe-57 Mossbauer spectroscopy showed that nickel and iron ions were oxidized simultaneously. The fraction of high-spin Fe4+ was related to the strong ligand field resulting from the presence of the prevailing Ni3+ and Ni4+ ions which lead to a lattice contraction. The behavior upon deintercalation of the Li(Ni0.90Fe0.10)O-2 phase was compared to that of two-dimensional LiFeO2. (C) 2000 The Electrochemical Society. S0013-4651(99)12-113-X. All rights reserved.