The 'concentration excessive potential refers to the limit of the concentration of electrode surface electrical active substances on current. In actual batteries, this effect is only mainly in relatively high current densities, especially in polymer cells, no flow electrolyte As, the concentration polarization is very serious because there is a lack of convection.
On the other hand, the migration of the migration of the moving ion is unchanged, even if there is no concentration polarization in the high magnification charge and discharge process. For liquid electrolyte phases, electrical active molecules or ions in electrode surfaces are supplemented by the following pathways: the mass of the body phase substance, or chemical reactions that occur in the electrolyte phase near the interface (independent of potential). The main mass transfer mechanism in the battery is the diffusion of the concentration gradient and electromigration in the electric field. If ions are only present in the electrolyte, the electromigration is very weak. However, when the electroactive substance is responsible for the delivery of all currents in the electrolyte phase, the electrode polarization and ohmic polarization are difficult to distinguish.
The battery electrode is typically a rough or porous substrate to increase the actual surface area of the electrode, which reduces the over-potential of the charge transfer process. However, when the quantity level of the surface is consistent with the thickness of the diffusion layer, it will be difficult to calculate the diffusion flow. . The porous structure changes the potential distribution and the microporous concentration gradient, thereby generating the dynamics and mass transfer control steps of charge transfer process. A large number of simple models (such as parallel, column microporous sequence model) have been studied.
So far, the study of concentration polarization is only concentrated on the consumption of electroactive substances of the phase electrolyte, and there is a metastable active surface decision if metal deposition and dissolution process. For most actual batteries, small current charging and discharge can be carried out under the open circuit; when the battery is charged, the ohmic polarization is generally the most significant polarization form, only in At a very high magnification, the concentration polarization is the main polarization form.
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