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Lithium-Ion Batteries: What They Are and Why They Explode

What exactly are lithium-ion batteries? Why do they explode? Everyday Einstein explores the answers.

By
Sabrina Stierwalt, PhD,
December 13, 2016
Episode #218

Page 1 of 2

Hoverboards, e-cigarrettes, cell phones, the Tesla Model S and a rescue robot made by NASA – what do they have in common? They have all made news recently for exploding due to faulty lithium-ion batteries. Just a few months ago, Samsung was forced to recall over a million of their newly released Galaxy Note 7 phones. So what are lithium-ion batteries, why do they keep exploding, and why do we keep using them? 

How Do Batteries Work?

The typical AA battery that goes into your television remote or your child’s singing toy, known as a dry cell or an alkaline battery, works via a chemical reaction. Within the battery, a chemical reaction causes electrons to build up at the anode, or the negative end of the battery. Since like charges, similarly to a bunch of electrons, want to repel each other, this build up is unstable.

Those electrons would prefer to spread out but are blocked from moving directly to the cathode, or the positive end of the battery, by a potassium hydroxide solution called an electrolyte. When you place the battery in your device, you create an alternate path for those electrons to reach the cathode. That path just so happens to send that charge through whatever it is you’re looking to power with your battery. The circuit is made complete by those same chemical reactions in the battery producing ions that serve to conduct current across the electrolyte.

Dry cell batteries will continue to supply electricity to your device until they run out of the substances producing the chemical reactions. Lithium-ion batteries work much in the same way, with a key difference being that they are rechargeable. In other words, they can put this reaction in reverse when hooked up to their own power source. When in use, lithium ions move through the electrolyte from the carbon anode to the lithium cobalt oxide cathode, but they move in the opposite direction when the battery is being charged.

Why Do Lithium-Ion Batteries Explode?

When a lithium-ion battery explodes, it is almost always because the battery was overheated. These batteries are equipped with a separator that prevents the cathode and anode from touching and a mechanism for forming lithium plates around the anode, and thus creating a short circuit, should the battery charge too fast. Both components are meant to keep the temperature under control and prevent what is called thermal runaway.

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