Composition–Valence Diagrams: A New Representation of Topotactic Reactions in Ternary Transition Metal Oxide Systems. Application to Lithium Intercalation

✍ Scribed by P. Strobel; F. Le Cras; M. Anne

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 398 KB
• Volume: 124
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1996.0211

✦ Synopsis

diagrams, and oxygen must be considered as a separate variable in the case of transition metals where oxidation Topotactic reactions in Li-M-O systems with M ‫؍‬ Mn, Ti, V, Fe are described in the framework of composition-valence states are variable. We shall show here that the classical diagrams, using the Li/M and the transition metal valence phase diagram based on an equilateral triangle is not al-(M) as coordinates. We show that this representation is very ways the most convenient way of presenting phase relations convenient to depict and compare the various parameters assoand especially topotactic reactions in ternary systems.

ciated with insertion/extraction reactions, i.e., the evolution of

The present paper describes an alternative representa-(M), the extent of intercalation x in Li x MO y , the electrochemition of ternary oxide systems: the composition-valence cal potentials, and the cell parameter changes. New directions diagram, which emphasizes transition metal valence and are suggested for topotactic reaction in oxides, especially in allows direct comparison of intercalation lines. The usetitanium ones. The composition-valence diagram helped in the fulness of such diagrams will be illustrated for systems detection of inconsistencies in the intercalation potentials in Li-M-O with M ϭ Mn, Ti, V, and Fe, and the intercalation LiFe 5 O 8 , which are corrected using new voltammetric data. We potentials in the spinel phases formed in these systems will conclude that lithium intercalation in octahedral sites of iron be discussed in more detail.

spinel oxides occurs at constant voltage around 1.6 V, whichever the Li-Fe-O host may be.