Nickel–iron battery

Lore & Background

Swedish inventor Waldemar Jungner experimented with iron substituting for cadmium in nickel–cadmium batteries in 1899, finding the iron version cheaper but less efficient and prone to hydrogen gassing. Thomas Edison patented and commercialized the nickel–iron battery in the United States in 1901, offering it for electric vehicles such as the Detroit Electric and Baker Electric. Edison claimed his design was far superior to lead–acid batteries, with higher energy density and faster charging, though it performed poorly at low temperatures and was more expensive. Edison's batteries were produced profitably from about 1903 to 1972 by the Edison Storage Battery Company in West Orange, New Jersey, then sold to Exide Battery Corporation, which discontinued the product in 1975.

The battery's active materials are held in nickel-plated steel tubes or perforated pockets. The positive plates contain nickel hydrate and pure flake nickel in alternating layers; the negative plates contain iron oxide tightly rammed into rectangular pockets. The electrolyte—a mixture of potassium hydroxide and lithium hydroxide—is not consumed during charge or discharge, so specific gravity does not indicate state of charge.

The cell's open-circuit voltage is 1.4 volts, dropping to 1.2 volts during discharge. Charging requires at least 1.6 volts per cell, and equalization uses 1.65 volts. The battery should not be charged from a constant voltage supply due to risk of thermal runaway.

Nickel–iron batteries were widely used for railway signaling, forklift, and standby power. Examples include London underground electric locomotives and New York City Subway R62A cars.

The technology has regained popularity for off-the-grid applications where daily charging is feasible. A modern development is the 'battolyser'—a combined battery and electrolysis system that produces hydrogen when fully charged, investigated for fuel cell cars and storage. The first industrial-scale battolyser was installed in 2023 at the RWE Magnum power gas plant in Delfzijl.

Reader's Guide

The nickel–iron battery's significance lies in its exceptional durability and tolerance of electrical abuse, making it suitable for long-term backup and cycling applications where other chemistries fail. Its ability to survive overcharge, overdischarge, and short-circuiting, combined with a potential lifespan of over 20 years under continuous charge, gave it a niche in railway signaling, subway cars, and standby power. However, its low specific energy, poor charge retention, and high manufacturing cost led to displacement by other rechargeable types in most applications. The battery's slow charge and discharge rates, due to low solubility of reactants, limit high-rate performance but preserve electrode life.

The technology has seen renewed interest for off-the-grid use and as a 'battolyser' for hydrogen production, leveraging its gassing behavior at full charge. Edison's original production ran from 1903 to 1975, but new manufacturers have since emerged in several countries. The battery's electrochemistry involves oxygen transfer between electrodes, sometimes called an oxygenlift cell, and its voltage characteristics differ from lead–acid in that electrolyte specific gravity does not indicate state of charge.

Did You Know?

• A 50 volt nickel–iron battery was the main DC power supply in the World War II German V-2 rocket.