Ionic mobility, field-enhanced

The field-enhancement ionic mobility can result from two different mechanisms. One is electrohydrodynamical (EHD) convection, which appears in its strong, turbulent form at 10 kV. According to this mechanism, ions are carried about by liquid flow, which is considerably faster than their own drift. The transport enhancement, T, is ... 

There exists another mechanism of field-enhanced mobility, but it needs a far higher applied voltage than EHD motion, and consequently has never been observed. Indeed, a classical rate-process approach of ionic diffusion and migration (see for instance Conway, 1970) shows that the drift velocity of an ion in the direction of the field is proportional to slnh (El/2 U), with 1 the mean jump distance of the ion from one site of low energy to another. If E 2 U/1, the drift velocity is proportional to E if E 2 U/1, however, it grows exponentially. 1 being about a few... 

Improvement of the ionic current by fast transport in the electrodes. High electronic mobility and low electronic concentration favor fast chemical diffusion in electrodes by building up high internal electric fields [14]. This effect enhances the diffusion of ions toward and away from the solid electrolyte and allows the establishment of high current densities for the battery. 

There is yet another effect that can play a role in the observed polarity dependence. If crystallization requires the rejection of a solute, then nucleation is aided in areas depleted of solute and continued growth requires, and becomes limited by, the diffusion of the rejected solute ahead of the moving interface. Thus the kinetics would be enhanced if the field gave the rejected solute an increased mobility (ionic conduction). The importance of this process is indicated by two observations of Uttecht etal (1970). First, they observe that in the AsnTe7Ge2 alloy the chemical composition of the crystalline filament is different from the glass from which it grows and second, they observe that many times the filament. 

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