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.
However, small manufacturing errors in the construction of the battery can lead to big problems. A stray metal fragment could puncture holes in the sealants that keep the battery parts separate and functioning. In the case of the Galaxy Note 7, the push to make our handheld devices smaller and thinner meant that a flaw in the construction of the battery placed the already very close cathode and anode ends a bit too close causing them to touch in several phones. Further stoking the flames, so to speak, is the fact that most electrolytes are flammable.
If these batteries are able to explode so easily, then why do we use them?
If these batteries are able to explode so easily, then why do we use them? Well, even after we consider safety, lithium-ion batteries still provide a large number of advantages over regular batteries. They are much lighter and, given that lithium is a highly reactive element, pack more punch for their size. Specifically, they can hold up to 160 Watt hours per kilogram which is around twice as much as a regular battery. They can be charged and recharged hundreds of times, and their discharge curve is longer and flatter than that for alkaline batteries giving them a consistent higher voltage throughout their lifetime.
Should You Avoid Lithium-Ion Batteries?
The short answer is: no, lithium-ion batteries are inescapable. They are used in laptops, portable music players, cell phones, digital cameras, and electric cars, just to name a few. Luckily, however, these high profile cases are actually statistically rare. For example, of the 2.5 million Galaxy Note 7 phones sold, there were between 26 and 55 reported cases of fires. So for every device that has a problem, there are hundreds of thousands more that were fine.
Scientists and battery manufacturers are also working on designing more durable separators and nonflammable electrolytes like those found in solid state batteries. You usually can’t spot a manufacturing error ahead of time, but you can look out for swelling in your battery (as the individual cells rupture) or unusual warmth. Remember also to never toss your old batteries in the trash which can send those chemicals into our soil and water—always bring them to a battery recycling program.
Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.
Image courtesy of shutterstock
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