Electrochemistry and structure of Li2-xCryMn2-yO4 phases

The synthesis of phases in the solid state solution series Li2CryMn2-yO4 wh ere 0 < y < 2 and their use as cathodes in lithium ion cells was reported p reviously [I.J. Davidson, R.S. McMillan, J.J. Murray, J. Power Sources,54(1 995) 205-208]. This paper reports the results of electrochemical evaluation s with metallic lithium anodes and on Rietveld refinements of X-ray and neu tron powder diffraction data for these phases. Although these materials are prepared at moderately high temperatures, the refinements show that they h ave a structure similar to the monoclinic layered form of LiMnO2 prepared b y soft chemistry at low temperatures by Armstrong and Bruce [A.R. Armstrong , P.G. Bruce, Nature, 381 (1996) 499-500] and by Delmas and Capitaine [C. D elmas, F. Capitaine, Extended Abstracts of the Eighth International Meeting on Lithium Batteries (1996) 470-471]. The degree of monoclinic distortion in the initial materials has an effect on the structural changes that occur on charging. The phases with a small monoclinic distortion change to an un distorted hexagonal structure on their first charge while those with a larg e monoclinic distortion change to a spinel-like structure on cycling. Crown Copyright (C) 1999 Published by Elsevier Science S.A. All rights reserved.