EFFECTS OF CHARGED OPEN-STAND IN NICKEL-HYDROGEN CELLS

Nickel/hydrogen cells used in spacecraft have to undergo planned and u nplanned open-stand during spacecraft testing and launching. The effec ts of different durations of such a stand on cell performance have bee n evaluated through tests conducted on a 36-Ah cell. Results indicate that: (i) the pressure loss is not an accurate indicator of the declin e in capacity, and (ii) open-stand results in electrode passivation. T he reactions responsible for pressure loss are not of the simple first -order type, but are more complicated. The passivation and history-dep endent pressure loss are due to the presence of hydrogen and two phase s of the nickel oxide (i.e., beta, gamma). These findings emphasize th at considerable care is necessary in handling nickel/hydrogen cells if passivation of the electrodes is to be avoided.