Why do lithium batteries explode?

EARLY FRIDAY MORNING, Samsung officially recalled millions of its popular new Galaxy Note 7 smartphones. dozens of reports of devices overheating, burning, and even exploding.

In fact, the Samsung incident is unusual only in scale, and in the company’s admirably aggressive response. Samsung hasn’t said specifically what’s causing the issue, but experts say it could have been any number of things. After all, that’s just what lithium ion batteries do. Well, bad ones, anyway.

There have only been 35 cases of the Galaxy Note 7 catching fire reported worldwide following 2.5 million sales, Samsung says.

The lithium ion batteries used by Samsung are common across the tech industry – so what makes them hazardous?

To understand why lithium ion batteries keep causing trouble, we’re going to need to do a very quick overview of how they work. They have three main components: an anode at one end, a cathode at the other, and an electrolyte between them. A voltage runs across it, driving lithium ions from one end to the other for charging and discharging (The cathode and anode are separated by an organic liquid called an electrolyte and a porous material called the separator. The lithium travels through the separator, within the liquid, between the two).

Causing explosions

Lithium-ion batteries seldom bulge or explode, but when they do, there are two leading causes. The first is a puncture, which might be caused by dropping your phone. A break in the thin compacted battery material between cells can produce to an internal short circuit, leading to swelling and potential explosions. Alternatively, cheaper batteries can sometimes accidentally feature rare microscopic metal particles inside that might come into contact with other parts of the battery cell, also leading to a short circuit.

With the Galaxy Note 7, Samsung and various reports suggest that the issue is caused when the device is charging, which leads us to our second major cause – heat. Excessive heat can again cause again internal short circuit within the battery, by breaking down the internal cells. However, this only usually occurs at very high temperatures, unless the battery is faulty. Overcharging may also be an issue, which is caused by batteries receiving more current than they can safely handle, causing them to overheat.

Too much heat in one area of the battery can lead to “thermal runaway”.  This happens when an area of a battery can’t cool down quickly enough, resulting in a breakdown chain reaction that generates more and more heat. In other words, excess heat causes a reaction that accelerates the temperature increase. Eventually, this can lead to a fire or explosion.  (If the battery charges too fast, generating heat, lithium plates form around the anode which can create a short circuit) 

“Normally you would have a battery management system that controls the rate at which you charge,” said Prof Grey.  

 “Batteries are optimised so that you don’t charge too fast – if you do that you will plate the lithium.” This is also why battery charging can be a frustratingly slow experience, she added.  

However battery packs – combining battery cells to generate more power – can be problematic and this is increasingly common. Batteries containing 12 cells, for example, are readily available for laptops.

“The more you put together, the higher the likelihood that some will fail,” said Prof Grey.

We should be clear though that Samsung has indicated that it is the batteries that are at fault in the Galaxy Note 7 and not any other part of the handset. It seems unlikely that the Galaxy Note 7 has be built in such a way that it is producing too much heat that makes it unsafe to stick a battery inside. Instead, it’s more likely that just a small percentage of the batteries that Samsung has purchased are not coping properly with the heat produced or current provided while charging. Either by not matching up to the required charging specifications or by simply coming from a faulty batch.

Protecting yourself

Without knowing exactly what is causing issues with Samsung’s Galaxy Note 7, we can’t say precisely how to avoid potential problems. However, there are some general tips to follow that can help protect yourself and your device from catastrophe. General warning signs that your battery is damaged and could explode include a hissing sound, popping, or swelling.

  • Stop charging your phone it if becomes too hot. Allow your phone to cool down before charging it again and make sure that you don’t cover your phone to let heat escape properly.
  • Stick to first-party chargers. Use the charger included in the box to make sure that your phone is receiving the optimal voltage and current. If you’re using a phone with a USB Type-C port or Quick Charge, it might be wise to stick with the cable that came in the box too.
  • Don’t charge your phone in bed. I know it’s very tempting to watch a video or read before you fall asleep, but you don’t want to roll over on your phone and have it overheat. Not to mention that leaving your phone under a pillow while it charges will cause it to heat up.
  • Be mindful of where you charge your phone. Avoid charging for long periods of time in really hot places, such leaving your phone on a car dashboard, next to a radiator, or in direct sunlight on hot days.

If you do happen to notice your battery swelling, unplug your phone and remove the battery, but only if the battery is user removable. Don’t attempt to dispose of the battery or device in the trash. Always get rid of your batteries at authorised disposal facilities or some electronics retailers, that offer battery recycling services.

Don’t miss: Samsung Galaxy Note 7 recall

If your battery and/or device is damaged as a result of a swollen or exploded battery, take your device to the retailer that you purchased it from or get in contact with the manufacturer. A replacement battery or device will usually be issued, especially if you have a warranty.

  

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