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How does a lithium-ion battery work?

You know that thermal runaway is a phenomenon that can affect lithium-ion batteries. In order to understand thermal runaway, it’s important to understand what a lithium-ion battery is – and what it does.

What does a lithium-ion battery do?

Cells in a battery store, transform, and conduct energy.

A lithium-ion battery and circuit transform electrochemical energy into electrical energy and transmit that energy as a current to a device, which is known in a circuit as a “load.”

The opposite reaction also occurs: When a battery is being charged, the movement of electrons and ions transforms electrical energy into electrochemical energy. The battery stores this electrochemical energy. 

Asset: How does a LIB work?
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Circuits

Batteries work within a circuit, which includes an energy source, a conductor, and a load (device receiving energy).

A short circuit occurs when electrical current flows on an unintended path where it meets too little resistance. A short circuit can happen inside or outside of a cell. The result is that too much electrical energy flows through this new path.

A short circuit within a lithium-ion battery can lead to thermal runaway.

Interested in learning more about short circuits? Check out this video.

Lab

Visualizing energy transfer

Through the bologna test, we can visualize some forms of energy transfer. You can replicate the bologna test or observe it through the video.

The bologna test is performed with a lithium primary cell, which is not rechargeable. Lithium primary cells are different from lithium-ion cells, which are rechargeable. However, you could expect a similar reaction from a lithium-ion battery.

Asset: The Bologna Test
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Your turn

Want to try the bologna test yourself? Make sure to follow the proper procedure and safety guidelines outlined in this demonstration guide.

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Challenge

What did we witness in the Bologna Test?

The saline solution conducts electrical energy from the battery to the bologna, which blackens.

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Inside a Lithium-Ion Battery

In the bologna test demonstration, you got to observe energy transfer external to a battery. Now, you can take a look inside a lithium-ion battery and discover what makes it work.

Asset: Lithium-Ion Battery Interior
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What’s inside a battery?

A lithium-ion battery is one type of battery. Lithium-ion batteries are powered by the movement of lithium ions between electrodes.

Lithium-ion batteries are often used because they:

  • are rechargeable
  • can transmit energy efficiently
  • store a large amount of energy in a small amount of space

In other words, lithium-ion batteries are small and powerful.

This is due to the chemical properties of lithium-ion battery components. Lithium-ion batteries can come in many types of shapes and sizes.

Asset: Lithium-Ion Battery Interior
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Asset: Alkaline Battery Interior
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Of course, lithium-ion batteries are not the only kinds of batteries that people use. Here, you can compare and contrast some of the internal differences between a lithium-ion battery and an alkaline battery, which is another common type of battery.

In this example, the lithium-ion battery has a “spiral-wound” construction, while the alkaline battery has a “bobbin” construction. That accounts for many of the physical differences you see.

Cells, batteries, and lithium ions

  • Cell: A battery cell stores, transforms, and conducts energy. 
  • Battery: A battery consists of one or more cells and a protective circuit board. It works in an electrical circuit.
  • Lithium ion: A lithium atom that has been ionized, meaning that it has an electrical charge because it has gained or lost an electron. In lithium-ion batteries, lithium is positive (Li+) because the atom has lost an electron.
  • Lithium-ion battery: A type of battery that is powered by the movement of lithium ions between electrodes. Lithium-ion batteries are especially small and powerful.

The charge and discharge process in a lithium-ion battery is exothermic, meaning it normally produces a bit of heat as a byproduct. It is normal for batteries to produce a small amount of heat.

Thermal runaway, however, is an abnormal production of heat. 

Reflect

Summarize your learning: How does a lithium-ion battery work?

Challenge

Building a problem definition for thermal runaway

Imagine you’re an engineer designing a new e-scooter. What unwanted energy changes will you need to consider to make a safe battery enclosure? Name the possible energy changes you can predict during charging and discharging and their potential risks.

Are you up for the challenge? Continue through the pathway to learn more about the problem of thermal runaway so you can solve the engineering design challenge. 

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