Solid Electrolyte Matrix Electrode Structures

Most battery electrodes are porous structures in which an interconnected matrix of solid particles, consisting of both nonconductive and electronically conductive materials, is filled with electrolyte. When the active mass is nonconducting, conductive materials, usually carbon or metallic powders, are added to provide electronic contact to the active mass. The solids occupy 50% to 70% of the volume of a typical poious battery electiode. Most battery electrode structures do not have a well-defined planar surface but have a complex surface extending throughout the volume of the porous electrode Macroscopically, the porous electrode behaves as a homogeneous unit. 

Incorporation into a Polymer Layer In recent years a new electrode type is investigated which represents a layer of conducting polymer (such as polyaniline) into which a metal catalyst is incorporated by chemical or electrochemical deposition. In some cases the specific catalytic activity of the platinum crystallites incorporated into the polymer layer was found to be higher than that of ordinary dispersed platinum, probably because of special structural features of the platinum crystallites produced within the polymer matrix. A variant of this approach is that of incorporating the disperse catalyst directly into the surface layer of a solid polymer electrolyte. 

A porous electrode consists of porous matrices of solids and void spaces. The electrolyte penetrates the void spaces of the porous matrix. In such an active porous mass, the mass-transfer condition in conjunction with the electrochemical reaction occurring at the interface is very complicated. In a given time during cell operation, the rate of reaction within the pores may vary significantly depending on the location. The distribution of current density within the porous electrode depends on the physical structure (such as tortuosity, pore sizes), the conductivity of the solid matrix and the electrolyte, and the electrochemical kinetic parameters of the electrochemical processes. A detailed treatment of such complex porous electrode systems can be found in Newman. ... 

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