The ability of these batteries to survive frequent cycling is due to the low solubility of the reactants in the electrolyte. The formation of metallic iron during charge is slow because of the low solubility of the ferrous hydroxide. While the slow formation of iron crystals preserves the electrodes, it also limits the high rate performance. These cells charge slowly, and are only able to discharge slowly. Nickel-iron cells should not be charged from a constant voltage supply since they can be damaged by thermal runaway. The cell internal voltage drops as gassing begins, raising the temperature, which increases current drawn and so further increases gassing and temperature.

The industry, however, would be greatly served by a nickel-iron battery having improved performance. Such batteries, having improved specific power and power density, would be greatly welcome. The uses of nickel-iron batteries would thereby be increased.

The present invention provides one with a battery having an iron anode, e.g., a Ni—Fe battery, having improved performance characteristics. The battery uses a particular electrolyte. The resulting characteristics of specific power and power density, as well as cycle life, specific energy and charge retention, are much improved over such iron anode batteries in the prior art.

Among other factors, it has been discovered that when using an iron anode in a battery, the use of a particular electrolyte enhances the performance characteristics of the battery significantly. The electrolyte is a sodium hydroxide based electrolyte. In one embodiment, a separator is used that is a non-treated polymeric separator, e.g., made from a polyolefin. The result is a battery of enhanced power, capacity and efficiency.