Nickel-iron battery

The nickel-iron battery (NiFe battery) is a storage battery having a nickel(III) oxide-hydroxide cathode and an iron anode, with an electrolyte of potassium hydroxide. The active materials are held in nickel-plated steel tubes or perforated pockets. In terms of energy density and cost, it is similar to a lithium-ion battery, although in terms of efficiency, self-discharge rate, and cell voltage, it is more similar to a nickel-metal hydride battery. It is a very robust battery which is tolerant of abuse, (overcharge, over-discharge, short-circuiting and thermal shock) 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. Its use has declined since production was halted by the destruction by fire of Edison's factory/laboratory in 1914 (13 separate "fireproof" concrete buildings), due to low specific energy, poor charge retention (similar to nickel-metal hydride), and poor low-temperature performance, and its high cost of manufacture, comparable with the best sealed lead-acid batteries and less than half the cost of nickel-metal hydride batteries.

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 Fe₃O₄. 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 batteries have long been used in European mining operations because of their ability to withstand vibrations, high temperatures and other physical stress. They are being examined again for use in wind and solar power systems and for modern electric vehicle applications.

The nickel-iron battery has been much improved upon since the days of Edison and is still manufactured today. A battery that lasts for decades (and in many cases, the equipment that it was originally designed to power) causes conspiracists to proclaim the battery as not common because it is "too good". In reality, the requirement of much nickel, a precious metal, in its production causes the cost of the battery to be representative of its durability. Therefore, lead acid, nickel-cadmium, lithium-ion and other much cheaper technologies have been deemed "durable enough" even though they do not last nearly as long as a nickel-iron counterpart.

Electrochemistry

The half-cell reaction at the cathode:

2 NiOOH + 2 H₂O + 2 e⁻ ↔ 2 Ni(OH)₂ + 2 OH⁻

and at the anode:

Fe + 2 OH⁻ ↔ Fe(OH)₂ + 2 e⁻

(Discharging is read left to right, charging is from right to left.)

History

Waldemar Jungner

Swedish inventor Waldemar Jungner had invented the nickel-cadmium battery in 1899. Jungner experimented with substituting iron for the cadmium in varying proportions, including 100% iron. Jungner had already discovered that the main advantage over the nickel-cadmium chemistry was cost, but due to the poorer efficiency of the charging reaction and more pronounced formation of hydrogen (gassing), the nickel-iron technology was wanting and was abandoned. Jungner never patented the iron version of his battery.

Thomas Edison

The battery was developed by Thomas Edison in 1901, and used 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). 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 power supply in the World War II German V2 rocket (together with two 16 volt accumulators which powered the four gyroscopes), with a smaller version used in the V1 flying bomb. (viz. 1946 Operation Backfire blueprints.)

Manufacture

Past

Edison's batteries were made from about 1903 to 1972 by the Edison Battery Storage Company located in East Orange, NJ. They were quite profitable for the company. In 1972 the battery company was sold to the Exide Battery Corporation, which discontinued making the battery in 1975. Edison was disappointed that his battery was not adopted for starting internal combustion engines and that electric vehicles went out of production only a few years after his battery was introduced. He actually developed the battery to be the battery of choice 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 ambient temperatures and were more expensive. The battery enjoyed wide use for railroad signaling, fork lift, and standby power applications.

Environmental impact

Nickel-iron batteries do not have the lead or cadmium of the lead-acid and nickel-cadmium batteries, which makes them a lesser burden on human and ecological health.