P. Křivák

Influence of grid design on current distribution over the electrode surface in a lead-acid cell

The current distribution over the plate surface in lead-acid cells was determined by means of a newly proposed method based on electrical measurements on a model. The method, which is much simpler than mathematical analysis of model systems, can be used to find the optimum grid design. Six illustrative examples and mathematical formulae for two special cases are presented.

Current distribution over the electrode surface in a lead-acid cell during discharge

The current distribution over the plate surface in lead-acid cells in the course of discharge was determined mathematically by using the equivalent circuit method. The dependence of the internal cell resistance on the current and charge passed was determined by measurements on a laboratory cell. Six cell variants were considered differing by the location of tabs serving as current terminals. The results are presented in the form of 3D diagrams at various states of discharge. To make the current distribution nearly uniform, extended current tabs located at opposite ends of the plate electrodes were proposed.

Resistance changes and premature capacity loss in lead battery plates

Our research work has been devoted to the identification of processes that cause premature capacity loss (PCL) in lead/acid batteries. Attention has been paid to the resistance of the active material and to the resistance of the interphase between the active material and the lead grid in specially prepared positive test electrodes, measured by an exact d.c. method. Resistance measurements performed on electrodes with grids from seven different lead alloys showed that PCL is related to increasing resistance of the active material. In contrast, PCL in electrodes having pure-lead grids is caused by the formation of an insulating layer on the grid surface, evidenced by the steeply rising interphase resistance.

A study of the effects of compression on the performance of the positive active mass in lead–acid cells using absorptive glass mat separators

Abstract A new electrochemical cell was designed and constructed to enable in situ measurements of the performance and internal resistances of lead–acid test electrodes in a vertical position during cycling at well-defined degrees of compression. The AGM separators used were combined with microporous paper separators to prevent short-circuiting by conducting bridges of lead dioxide. The test cells were subjected to pressures in the range 0–8 N/cm2; the compression decreased the positive active mass resistance and increased its cycle life.

Study of resistance changes related to premature capacity loss in lead battery plates

Measurements of the resistance of the active material and of the interphase between the active material and the lead grid were performed by an exact d.c. method during cycling under two different regimes using specially prepared positive test electrodes with grids from seven different lead alloys. The results were compared with those obtained earlier by using a higher (1 h) discharge rate. In both cases, the premature capacity loss was caused by a low charging rate and it was related with increasing resistance of the active material, although the cycle life was distinctly longer at the lower (4 h) rate of discharge. The interphase resistance values of the individual ribs show a scatter which becomes very pronounced at the end of the cycle life, indicating a degradation of the porous electrode structure, often manifested by shedding of the active material.

Analysis of positive-plate resistance during cycling and the effect of compression

Abstract An electrochemical cell is designed and constructed to enable in situ measurements of the resistance of both the active mass and the interphase between the current-collector and the active mass in lead/acid test electrodes during cycling at well-defined degrees of compression ranging from zero to 90 kPa. Preliminary results of measurements on positive electrodes are well reproducible and show that after conditioning cycle, both the interphase resistance and the active-mass resistance are independent of compression. Time changes of the two resistances are also studied and discussed.

Optical sensors for the free space optical link

This work deals with a review of the possible principles and construction of the terrestrial optical wireless links and the problematic of the proper photodiode and laser diode selection according to the wavelength dependent atmospheric transmittance and the photodiode sensitivity. For the calculations we used the power balance equations and the catalog values of the available laser diodes and detectors. For the most commonly used free space optical links, the laser diode price and the maximum power are also considered.