Cathode reaction types solid solution

Layered and spinel materials have been used successfully as intercalation-type cathode active materials in commercial Li-ion batteries. The physical and chemical properties, electrochemical reactions, structure evolution mechanisms, stability and safety issues have been widely investigated. Based on comprehensive fundamental researches, since 1980s, their electrochemical performances are improved continuous after various modifications, such as doping, surface coating, forming solid solution and composite, controlling morphology, size and crystallinity. Here, basic features of layered and spinel materials are summarized. 

Electrode processes are a class of heterogeneous chemical reaction that involves the transfer of charge across the interface between a solid and an adjacent solution phase, either in equilibrium or under partial or total kinetic control. A simple type of electrode reaction involves electron transfer between an inert metal electrode and an ion or molecule in solution. Oxidation of an electroactive species corresponds to the transfer of electrons from the solution phase to the electrode (anodic), whereas electron transfer in the opposite direction results in the reduction of the species (cathodic). Electron transfer is only possible when the electroactive material is within molecular distances of the electrode surface thus for a simple electrode reaction involving solution species of the fonn... 

FIGURE 22.21 Polarization curves for the corrosion of a photoexcited n-type GaAs electrode in 0.5 kmol m-3 sulfuric acid solution [15] curves are exaggerated around Ecolr solid curve = photoexcited, dashed curve = dark, and H2 = cathodic hydrogen reaction coupled with anodic GaAs dissolution. 

There are two main types of PEC cells, the regenerative type cells, and the photoelectrolysis cells. The first type also called liquid-junction solar cells, serve like solid-state cells for solar energy conversion into electricity. The same reaction proceeds at both electrodes of the cell, directed forward at the anode, backward at the cathode. Hence, composition of the solution is preserved unchanged. The other type, the photoelectrolysis cells serve for conversion of solar energy into chemical energy. Here, two different reactions proceed at the electrodes. As a consequence, certain substance in the cell is transformed in the course of its operation. These two types of the PEC cells are described in more detail below. 

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