Topotactic insertion reaction materials

The thermodynamic properties of topotactic insertion reaction materials with selective equilibrium are quite different from those of materials in which complete equilibrium can be assumed, and reconstitution reactions take place. Instead of flat plateaus related to polyphase equihbria, the composition-dependence of the potential generally has a flat S-type form. 

Originally, this referred specifically to layered structures that can undergo insertion of ions or molecules between the van der Waals gaps, but is now commonly used for any structure that undergoes topotactic insertion reactions. For Li-ion battery materials, it refers specifically to compounds that undergo reductive insertion of lithium ions, such as graphite (used as an anode) or LiCo02 (used as a cathode). 

Bruce PG, Irvine ITS (2001) Insertion Compounds. In Encyclopedia of Materials Science and Technology, Elsevier Science Ltd Oxford ISBN 0-08-0431526, pp. 4115-4121 SchoUhom R (1980) Reversible topotactic redox reactions of solids by electron/ion transfer. Angew Chem Int Ed Engl 19 983-1003... 

Insertion (intercalation) compounds. Insertion compounds are defined as products of a reversible reaction of suitable crystalline host materials with guest molecules (ions). Guests are introduced into the host lattice, whose structure is virtually intact except for a possible increase of some lattice constants. This reaction is called topotactic. A special case of topotactic insertion is reaction with host crystals possessing stacked layered structure. In this case, we speak about intercalation (from the Latin verb intercalare, used originally for inserting an extra month, mensis intercalarius, into the calendar). 

Insertion and intercalation electrode materials are electroactive and have composition, chemical and physical properties that change with oxidation state. The materials have a common characteristic that they serve as a host solid into which guest species are inserted from an electrolyte, and the insertion process is reversible. In particular, the intercalation process is described as the reversible insertion of guest species into a host lattice without structural modification of the host. The term topotactic or topochemical is also used to describe the insertion reaction. 

Furthermore, the topotactic insertion/extraction reactions may occm by diSusion in onedimensional channels as in the hexagonal tungsten bronze, in two-dimensional as in layered transition metal dichalcogenides, or in three-dimensional as in the close-packed spinel structure. There are a large number of candidate materials which can be used in lithimn insertion... 

The reactions of these insertion materials, except for LiMnO, [19, 20], consist of electron and lithium-ion insertion into, or extraction from, each matrix without the destruction of its core structure this is called a topotactic reaction. A series of LiCovNi, v02 (0 < y < 1)) and... 

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