Negative plates capacity

D. G. Vella, L.H. Vu, ALABC Project N1.2, Overcoming negative-plate capacity loss in VRLA batteries cycled under partial-state-of-charge duty. Final Report, July 2000 to June 2002, Advanced Lead-Acid Battery Consortium, Research Triangle Park, NC, USA, 2002. 

Under conditions where the capacity of the detector cell is less than the plate capacity of the column (Casignal dominates. Conversely,... 

The dipole moment of a molecule can be obtained from a measurement of the variation with temperature of the dielectric constant of a pure liquid or gaseous substance. In an electric field, as between the electrostatically charged plates of a capacitor, polar molecules tend to orient themselves, each one pointing its positive end toward the negative plate and its negative end toward the positive plate. This orientation of the molecules partially neutralizes the applied field and thus increases the capacity of the capacitor, an effect described by saying that the substance has a dielectric constant greater than unity (80 for liquid water at 20°C). The dipole moments of some simple molecules can also be determined very accurately by microwave spectroscopy. 

Even though this contribution is always negative, the total capacity must be positive - otherwise the capacitor would accumulate charge spontaneously. Thus Eq. (17.4) is only valid if f > rjm, so that there is no electronic overlap between the two plates. Similarly the use of a macroscopic dielectric constant in Eq. (17.5) presupposes a plate separation of macroscopic dimensions, and again the total capacity is positive. Only unphysical models or bad mathematical approximations can produce negative interfacial capacities, which enjoyed a brief spell of fame under the name of the Cooper-Harrison catastrophe [2]. 

On the other hand. AGM separators offer little control over the oxygen transport rate or the recombination process. The arrival of too much oxygen to the negative plate could result in overheating, hindrance of the battery s ability to recharge, or even a loss of capacity. Furthermore. AGM separators exhibit low puncture resistance. 

It is seen that the major effect on peak shape is the "detector cell capacity V column plate capacity" ratio, (CJ. When the capacity of the detector cell is less than the plate capacity of the column, (C <1), the negative part of the signal dominates, and when the detector cell capacity exceeds the column plate capacity, (C >1), the positive part of the signal dominates. For this reason when (C >1), the integral curve rises to a maximum but does not return to the baseline. Conversely, when (C <1), the integral curve first rises and then falls below the baseline and does not return. 

In VRLA batteries, oxygen reaches the negative plates and is reduced to form water. It also oxidizes the expander and thereby produces carbon dioxide. Consequently, the morphology of the secondary Pb crystals is changed and they become dendrite-like, similar to those shown in Fig. 3.57(a). This results in capacity... 

The addition of sulfates to the positive plate was evaluated by Lorenz (as described in Ref. 58). Results showed that 0.5wt.% barium sulfate or strontium sulfate added to the positive active-material reduced the cycle-life from 100 cycles without the additive to 30-50 cycles with the additive under the same conditions. The end-of-life was taken as a 40% decline in the initial capacity. Lorenz further reported that calcium sulfate is not isomorphous with lead sulfate and therefore has no effect on battery life. (Note, calcium sulfate also does not act as an inorganic expander for negative plates.)... 

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