The voltage of an electrochemical cell, i.e. the difference between the chemical potentials of the two electrodes, may play the role of a sensor which allows to display the structural modifications and the physical properties. The electrochemical processes involved in an alkali metal (A) intercalation electrode emphasize the influence of the ionic and/or electronic features. The A+-lattice and A+-A+ interactions as well as electronic band-filling may lead to phase transitions or even limit the intercalation reaction.
The shape of the cell voltage vs. intercalation rate curve depends on the number of vacant sites available for intercalation, the number and the oxidation state of the reducible cations, the band structure of the material and the covalency of the framework.
Alkali ion intercalation in 3D-structures related to perovskite (Ln⅓ NbO3), hexagonal tungsten bronze (LiW3O9F) and Nasicon-type (AM2 (PO4)3) is discussed from that point of view.
In Ln⅓NBO3 (Ln = La, Nd) (i.e. ▭ ½Ln⅓ ▭, ⅙NbO3) L1+-intercalation in various sites is related to the rare earth size.
Two extra lithium atoms can be introduced into LiW3O9F in which four sites are available, but only one out of two is occupied in order to reduce the electrostatic interactions. Moreover the change in the discharge curves can be associated to the modifications with intercalation rate of the Li+-lattice interactions.
Within the Nasicon derived structures of ATi2 (PO4)3 and Fe2 (MoO4)3 the intercalation process is limited by the lowest stable oxidation state of titanium or iron. In both systems the strong electronic localization leads to formation of large two phase-domains.
The relevance of using 3D-intercalation electrodes in electrochemical power batteries will be discussed as far factors such as electrical behavior or absence of significant unit cell modifications of the positive electrodes during the intercalation process are essential for many cycle utilizations.