Intercalation insertion compounds

Fig. 6. Structural and stoichiometric aspects of graphitic and organic intercalation (insertion) compounds.

Their positive electrode materials are lithium intercalation (insertion) compounds such as... 

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). 

Intercalation and insertion compounds are another class of ionically condncting solids. These materials are mixed ionic and electronic conductors and are also covered by a separate article (see Intercalation Chemistry). 

Insertion compounds 308, 323 Insertion electrode 316, 320, 326 Intercalation potential 338, 341 Intergranular attack 147 Intramolecular charge-transfer state 33, 35, 37, 55... 

Lithium intercalation of compounds such as SnS2 are of technical interest for pho-tochromic display materials and lithium electrodes which reversibly take up and release Li". Li and Sn NMR has been used to investigate the location of the Li insertion sites in this material (Pietrass et al. 1997). The Li spectra show a central transition which can be decomposed into 2 components with different xq values corresponding to Li in octahedral and tetrahedral interlayer sites. As the Li concentration increases, the additional ions enter tetrahedral intralayer sites surrounded by 3 tin and 4 sulphur atoms and characterised by a broad Li NMR spectral component. Further insertion of Li results in the material becoming amorphous by rupture of the layers (Pietrass ef a/. 1997). 

For most insertion compounds, the interaction of intercalated ions with each other in the host lattice is not negligible. In order to simply consider the contribution of ionic interaction in Equation (5.8), it is often assumed that each ion experiences a mean interaction or energy field from its neighboring ions, based on a mean-field theory [10]. According to this approximation, the contribution to the chemical potential is proportional to the fraction of sites occupied by the ions 5, and hence the interaction term is introduced into Equation (5.8) as... 

Intercalation compounds are formed from layered structures with additional atoms or molecules between the layers, insertion compounds when atoms enter a three-dimensional framework. Many of these compounds are nonstoichiometric. 

As explained in Topic B6 the synthesis of solids often requires high temperatures, because of the slow diffusion of atoms. In intercalation compounds and some insertion compounds however, diffusion of guest species is more facile, and such compounds can often be made prepared under fairly mild conditions, sometimes known as chimie douce ( gentle chemistry ). Intercalation compounds of graphite can be made directly by exposure of the solid to Br2 or to alkali metal vapors. 

Polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, and poly-methylthiophene may exhibit a mixed electronic and ionic conductivity, similar to inorganic intercalation, or insertion compounds [43]. In the conductive form these polymers are partly oxidized and these positive charges are equilibrated by inorganic anions, which can diffuse through the polymer net. Alternatively, the conductive polymers can be partly reduced, with cations as counter ions. The eleetronic conductivity originates Irom partial oxidation of conjugated jt-bonds. The positive charge... 

Intercalation compound (host material, insertion compound)... 

Fig. 3.1 The types of insertion compounds as a function of the dimensionality. Red circles are intercalated ions across the host channels...

Dickens PG, Pye MF (1982) Oxide insertion compounds. In Whittingham MS, Jacobson AJ (eds) Intercalation chemistry. Acadtanic, New York, pp 539—561... 

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