Effect of Cobalt Additive, KOH Concentrations, and Types of Nickel Electrodes on Storage Behavior of Nickel-Hydrogen Cells

Open circuit storage tests of discharged Ni/H₂ cells have been carried out at 20°C to understand effects of cell design parameters on capacity fading with storage and determine capacity fading mechanism. Cell design parameters studied include variations in the electrode substrate (dry powder or wet slurry sinter), active material impregnation technique (alcoholic or aqueous bath), cobalt additive concentrations (4 to 10%), KOH concentration (26 or 31%), and cell precharge (nickel or H₂). Precharge had the most dominant effect of all parameters. When cells had nickel precharge, virtually no fading was observed with storage up to 188 days, while gradual fading was observed with all H₂ precharged cells. Tendency of capacity fading of these cells depended on KOH concentration, impregnation technique, and cobalt concentration. Cell pressure changes with storage were consistent with build-up of electrochemically undischargeable active material with capacity fading. Overcharging at low temperature (0°C) was effective in partial recovery of capacity but low-earth-orbit cycling had a minimal effect.