Nickel–iron battery

Key takeaways

Nickel–iron battery belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Nickel–iron battery to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Nickel–iron battery from memory before moving on to harder problems.

Reference excerpt

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. 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 temperature, which increases current drawn and so further increases gassing and temperature.

Electrochemistry The half-cell reaction at the positive plate from black nickel(III) oxide-hydroxide NiO(OH) to green nickel(II) hydroxide Ni(OH)2 :

2 NiO ( OH ) + 2 H 2 O + 2 e − ↽ − − ⇀ 2 Ni ( OH ) 2 + 2 OH − {\displaystyle {\ce {2 NiO(OH) + 2 H2O + 2 e- <=> 2 Ni(OH)2 + 2 OH-}}}

and at the negative plate:

Fe + 2 OH − ↽ − − ⇀ Fe ( OH ) 2 + 2 e − {\displaystyle {\ce {Fe + 2 OH- <=> Fe(OH)2 + 2 e-}}}

(Discharging is read left to right, charging is from right to left.) The open-circuit voltage is 1.4 volts, dropping to 1.2 volts during discharge. The electrolyte mixture of potassium hydroxide and lithium hydroxide is not consumed in charging or discharging, so unlike a lead-acid battery the electrolyte specific gravity does not indicate state of charge. The voltage required to charge the NiFe battery is equal to or greater than 1.6 volts per cell. The inclusion of lithium hydroxide improves the performance of the cell. The equalization charge voltage is 1.65 volts.

History

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Illustrations

Worked examples

Example 1 — a first encounter with Nickel–iron battery

Start with the simplest possible case. Write down what Nickel–iron battery claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nickel–iron battery before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nickel–iron battery ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nickel–iron battery

In research: Nickel–iron battery appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Nickel–iron battery in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Nickel–iron battery is common in secondary-school and first-year university syllabi. It links to neighbouring topics Iron, Nickel, Rechargeable batteries, so understanding it makes those chapters shorter.
In everyday life: Look for Nickel–iron battery outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Nickel–iron battery in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Nickel–iron battery means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Nickel–iron battery out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nickel–iron battery in simple terms?

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.

Why does Nickel–iron battery matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nickel–iron battery?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nickel–iron battery.