PROTON INSERTION REACTIONS IN LAYERED TRANSITION-METAL OXIDES

The several different types of insertion reactions are briefly reviewed, and an example, the so-called ''nickel electrode'', which actually involves a proton-driven reaction between Ni(OH)2 and NiOOH is discussed in some detail. This electrode has been widely used in battery technology, e.g. on the positive side of Cd/Ni, Zn/Ni, Fe/Ni, H-2/Ni, and metal hydride/Ni cells, in some cases for a very long time. It has relatively rapid kinetics and exhibits unusually good cycling behavior. This is directly related to its mechanism of operation, which involves a solid state proton insertion reaction. While the attractive properties of this electrode have led to many investigations, there are still a number of aspects of its operation that are generally not understood, but can be explained in terms of the microstructural and thermodynamic aspects of this insertion reaction.