The nickel-iron rechargeable battery was introduced at the turn of the 20th century in Europe by Junger and in the United States by Thomas Edison. As designed by Edison this type of cell is practically indestructible physically and can withstand electrical abuse such as overcharge, over-discharge, short circuiting and standing discharged for long periods. Such characteristics make it a desirable technology for many applications especially as standby power, electric cars and other mobile traction applications. The battery is best applied where high cycle life at repeated deep discharges is required or where long standby life is required such as 10 to 20 years. The cost of the nickel-iron battery lies between the lower cost lead acid and the more expensive nickel-cadmium battery. The listed advantages of these batteries include reliability and robustness of physical structure, and forgiving electrical characteristics allowing over charge and discharge. As disadvantages it has a low energy density (30 Wh/kg) , low power density (25W/kg), poor low temperature performance and is easily damaged by high temperatures.
The active materials used in construction of a cell of this type include, a metallic iron negative electrode, a nickel oxide positive electrode and a potassium hydroxide solution with lithium hydroxide for the electrolyte. The overall reversible chemical reaction is :
3Fe + 8NiOOH + 4H2O = 8Ni(OH)2 + Fe3O4
Nickel-iron batteries have been made in recent years in sizes ranging from 5 to 1250 Ah. However recently they have become less popular being replaced by lead acid and Nickel Cadmium batteries and are no longer manufactured by many of the original manufacturers.
Advancements in Nickel-iron batteries.
Some of the physical and electrical advantages of this battery previously described have caused renewed research interest in developing this technology further. The advanced battery utilizes sintered-fiber metal (steel wool) plaques, impregnated with active material, for both the positive and negative electrodes. Non-woven polypropylene sheets are used as separators between the electrodes. The techniques for making these new type nickel-iron batteries for high production more closely match that of the lead acid battery allowing a lower cost. Westinghouse has developed one such system and as such has reported the following performance characteristics.
Specific energy = 55 Wh/kg
Energy density = 110 Wh/L
Specific power = 100 W/kg
Cycle life > 900
Projected production cost = 200 to 250 $/kWh
Several other companies have developed similar cells using sintered-nickel electrodes such as The Eagle Pritcher Company and the Swedish National Development Corp with reported similar operating characteristics.
