Thermal Runaway Causes Phone Explosions
Whenever a Li-ion battery explodes or catches fire, it’s undergoing a process called thermal runaway. This process can be a bit difficult to understand, so we’ll keep things short, sweet, and free of dense scientific jargon.
Lithium-ion batteries contain a ton of Li-ion cells. Each of these cells has a critical temperature—think of it as a boiling point. When the critical temperature of a cell is reached (due to external heat, overcharging, damage, or poor manufacturing), it enters an exothermic breakdown. Basically, the cell itself starts to release a ton of heat.
This kicks off the process of thermal runaway, which is essentially a positive feedback loop (like when you put a microphone next to a speaker). Once a cell enters exothermic breakdown and releases heat, its neighboring cells are destined to hit their own critical temperatures. Depending on the speed of this process, a battery could quietly sizzle out, catch fire, or create a minor explosion.
Now that we understand the process of thermal runaway, it’s a lot easier to pinpoint how, when, and why phones (among other Li-ion devices) explode.
If your phone or another device has a swollen battery, however, you’ll want to do something about that right now.
RELATED: What to Do When Your Phone or Laptop Has a Swollen Battery
Don’t Leave Your Phone in the Car
If you live in a snowy area, you’re probably aware that car batteries work best when they’re a little warm—say, 80 degrees Fahrenheit. You’re probably also aware that too much heat can ruin a battery, along with other components in a car. Well, the same goes for phone batteries.
When a Li-ion battery discharges at a high temperature (sitting outside or in a car), its cells can become a bit unstable. They may not enter an exothermic breakdown, but they can permanently short, deteriorate, or (oddly enough) produce gases like oxygen and carbon dioxide. These gases can cause the battery to inflate like a balloon, which creates pressure (energy that can cause an explosion) or compromise the battery’s structure.
Naturally, this process can accelerate if a Li-ion is charging while at a high external temperature. That’s why most phones will stop the charging process or shut down if they get too hot.
That said, your phone probably won’t explode after being left in a hot car for a day. And while permanent shorts and pressure buildup can lead to thermal runaway, these slow forms of mechanical deterioration usually cause a battery to break before it has the chance to explode. Plus, phones and Li-ion batteries have built-in safety features that prevent slow-forming mechanical issues from getting out of hand. Just keep in mind that those safety features usually lead to the death of your phone.
Use Reliable or Certified Charging Devices
Generally speaking, any charger will work with any device. An old or cheap micro-USB cable will work with newer phones, and a brand new super fast charger will work with old devices. But you should probably stick with reliable chargers from good companies, or chargers that are certified by your phone’s manufacturer.
Cheap or uncertified chargers (especially crappy wireless chargers) can generate excess heat and damage a phone’s battery. Usually, this damage happens over a long period, and it leads to “bubbles” or shorts in your phone’s battery. Again, this kind of slow-forming mechanical damage will almost always break your phone before it can burst into flames.
But don’t worry, a cheap charger won’t “overcharge” your phone (although that would undoubtedly cause an explosion). Phones have built-in voltage limiters that prevent overcharging or charging that’s “too fast” for the battery to handle.
Don’t Bend or Stab Your Phone
When a Li-ion battery is physically damaged, it can short circuit, build up gases, or burst into flames on the spot. Unless you’re taking apart your phone or breaking it for fun, this isn’t an issue that you need to worry about. When dropping a phone, important components like the display will usually break before the battery takes any damage.
Why does this happen? Well, Li-ion batteries contain a thin sheet of lithium and a thin sheet of oxygen. An electrolyte solution separates these sheets. When that solution is ruptured or punctured, the layers of lithium and oxygen react, which initiates an exothermic breakdown and thermal runaway.
In some cases, this can occur while replacing a phone’s battery. Puncturing or bending a Li-ion can create mechanical failures, and if a battery isn’t correctly handled during installation, it can catch on fire (immediately or over time). Recently, a woman’s iPhone caught on fire after she had the battery replaced at an unofficial repair shop, and some Apple Stores have dealt with fires while replacing iPhone 6 batteries.
Also, just as a side note, don’t stab batteries for fun. You might be able to avoid a fire or a minor explosion, but you won’t be able to avoid the toxic gas that’s released by a burning li-ion battery.
Most Phone Explosions Are Due to Bad Manufacturing
While overcharging and overheating sound like dangerous, battery-bursting nightmares, they rarely cause fires or explosions. Slow-forming mechanical failures tend to break a battery before it has the chance to enter thermal runaway, and built-in safety features prevent these failures from getting out of hand.
Instead, a phone’s fate is usually determined during the manufacturing process. If a phone is destined to explode, then there isn’t much that you can do about it.
Li-ion batteries contain lithium, an incredibly unstable metal. That instability is great for holding and transferring electricity, but it can be disastrous when improperly mixed with other metals. Sadly, Li-ion batteries also have to contain nickel, cobalt, and graphite. During the manufacturing process, these metals can form deposits on manufacturing equipment, which can then contaminate a Li-ion battery’s innards and cause chemical instability, short circuits, and explosions.
Poor assembly can also be an issue. Like a skyscraper or a car, Li-ion batteries are welded together from a variety of bits and pieces, and bad welding can create a lot of electrical resistance. This resistance (friction) generates heat, which can cause short circuits and mechanical issues over a very short period.
Relax, Your Phone Probably Won’t Explode
During the whole Galaxy Note 7 controversy, between 90 and 100 Note 7s exploded, caught fire, or overheated. That’s less than 1% of the 2.5 million Note 7s that Samsung shipped to stores. Sure, Samsung’s global recall probably kept these numbers from going any higher, but it’s clear that phone explosions are extremely rare.
That said, you should still be mindful of exploding phones. Avoid buying phones that are brand new, and do a quick Google search before getting a new phone. And while slow-forming mechanical issues rarely lead to phone explosions, it’s not a risk that’s worth taking. Don’t leave your phone in the hot car, try to use reliable or certified charging devices, and please, don’t stab or bend your phone.
RELATED: Debunking Battery Life Myths for Mobile Phones, Tablets, and Laptops
Sources: Natural Communications/PMC, Battery University, Battery Power, Michigan Engineering
