Volume Tolerance Characteristics of a Nickel-Hydrogen Cell
AEROSPACE CORP EL SEGUNDO CA TECHNOLOGY OPERATIONS
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The volume tolerance characteristics of a nickel-hydrogen cell were evaluated by altering the volume of electrolyte within the cells components. This was done by evaporating increments of water from a cell and evaluating the cells 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 chargedischarge cycles were carried out following each water removal step. The discharge was programmed such that the cell was discharged at the C, C2, and C4 rates during the 100 depth-of-discharge. The discharge cycle was completed at the C4 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 C2 rate after 57 ml of water had been removed from the cell. This represented a 26.7 reduction in the electrolyte volume. At this point, the static model estimated that only 15 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. During normal life cycle testing or mission applications, all three of these factors take place at the same time.
- Electrochemical Energy Storage