Volume tolerance characteristics of a nickel-hydrogen cell

The volume tolerance characteristics of a nickel-hydrogen cell were evaluated by altering the volume of electrolyte within the cell´s components. This was done by evaporating increments of water from a cell and evaluating the cell´s performance following each removal. The cell selected for this investigation was one that was sensitive to electrolyte volume reductions due to having only one layer of zircar separator. Two complete charge/discharge cycles were carried out following each water removal step. The discharge was programmed such that the cell was discharged at the C, C/2, and C/4 rates during the 100% depth-of-discharge. The discharge cycle was completed at the C/4 discharge rate to a 1.0-V cutoff voltage. Static modeling of this particular cell design permitted estimates to be made of the electrolyte content of the separator, the negative electrode, and the positive electrode following each increment of water removal. As expected, the internal impedance of the cell increased as the separator dried out, but there was no reduction in usable capacity at the C/2 rate after 57 ml of water had been removed from the cell. This represented a 26.78 reduction in the electrolyte volume. At this point, the static model estimated that only 34% of the pores within the separators were filled with electrolyte. These estimates of electrolyte content of the separator can be translated into estimates of cell performance following different amounts of electrode swelling and plaque corrosion that would result in equal amounts of electrolyte loss from the separator