thumb|Thomas Edison in 1910 with a nickel-iron cell from his own production line
The nickel–iron battery (NiFe battery) is a rechargeable battery having nickel(III) oxide-hydroxide positive plates and iron negative plates, with an electrolyte of potassium hydroxide. The active materials are held in nickel-plated steel tubes or perforated pockets. It is a very robust battery which is tolerant of abuse, (overcharge, overdischarge, and short-circuiting) and can have very long life even if so treated.
It is often used in backup situations where it can be continuously charged and can last for more than 20 years. Due to its low specific energy, poor charge retention, and high cost of manufacture, other types of rechargeable batteries have displaced the nickel–iron battery in most applications.
Uses
Many railway vehicles use NiFe batteries. Some examples are London underground electric locomotives and New York City Subway car – R62A.
The technology has regained popularity for off-the-grid applications where daily charging makes it an appropriate technology.
Battolyser
When nickel-iron and lead batteries are fully charged they start to produce hydrogen, which was seen as a disadvantage. Now, nickel–iron batteries are being investigated for use as combined batteries and electrolysis for hydrogen production for fuel cell cars and storage. These "battolysers" could be charged and discharged like conventional batteries, and would produce hydrogen when fully charged. 'Battolyser' is a registered trademark of the Dutch spin off of the University of Delft Battolyser Systems. In 2023 Battolyser has installed the first industrial-scale Battolyser system at the RWE Magnum power gasplant in Delfzijl.
Durability
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.
The open-circuit voltage is 1.4 volts, dropping to 1.2 volts during discharge.
In 1901 Thomas Edison patented and commercialized NiFe in the United States and offered it as the energy source for electric vehicles, such as the Detroit Electric and Baker Electric. Edison claimed the nickel–iron design to be, "far superior to batteries using lead plates and acid" (lead–acid battery). Edison had several patents: /1901, /1902, and German patent No 157.290/1901. for electric vehicles, which were the preferred transportation mode in the early 1900s (followed by gasoline and steam). Edison's batteries had a significantly higher energy density than the lead–acid batteries in use at the time, and could be charged in half the time; however, they performed poorly at low temperatures, and were more expensive.
Jungner's work was largely unknown in the US until the 1940s, when nickel–cadmium batteries went into production there. A 50 volt nickel–iron battery was the main D.C. power supply in the World War II German V-2 rocket, together with two 16 volt batteries which powered the four gyroscopes (turbine powered generators supplied A.C. for its magnetic amplifier driven servomechanisms). A smaller version was used in the V-1 flying bomb. (viz. 1946 Operation Backfire blueprints.)
Edison's batteries were profitably made from about 1903 to 1972 by the Edison Storage Battery Company in West Orange, New Jersey. In 1972 the battery company was sold to the Exide Battery Corporation, which discontinued the product in 1975. The battery was widely used for railroad signaling, forklift, and standby power applications.
Nickel–iron cells were made with capacities from 5 to 1250 Ah. Many of the original manufacturers no longer make nickel iron cells,
thumb|The elements of a nickel iron (NiFe) cell
The active material of the positive plates is a form of nickel hydrate. The tube retainers are made of thin steel ribbon, finely perforated and nickel-plated, about 4 in. long and 1/4 in. and 1/8in. in diameter. The ribbon is spirally wound, with lapped seams, and the tubes reinforced at about 1/2 in. intervals with small steel rings. Into these tubes nickel hydrate and pure flake nickel are loaded in thin, alternating layers (about 350 layers of each to a tube) and are tightly packed or rammed. The purpose of the flake nickel is to make good contact between the nickel hydrate and the tubes, and thereby provide conductivity. The tubes, when filled and closed, are then mounted vertically into the grids.