A selection of AA batteries
Lithium-ion (LI) batteries have become a major part of daily life in the last decade. They’re in your camera, your phone, your computer, and maybe even in your car. There are tremendous advantages to LI batteries over other types of batteries; they are much lighter weight and a lower rate of energy loss, but there’s a fine line that has to be walked to keep the more energetic LI composition safe.
A battery is a chemical reaction that you can keep in your pocket. LI batteries use a lithium electrolyte to create the chemical reaction that allows you to power your phone; lithium salt gel is wrapped in a thin, non-reactive envelope and connected to a positive and a negative electrodes which are separated so they can’t touch. When phone batteries explode it’s because one way or another the lithium electrolyte gel has come into contact with other metals in your phone and caused a reaction.
Sometimes this contact is caused by “thermal runaway” – overheating that causes the volatile electrolyte to continue reacting even if it isn’t connected to a power source. Thermal runaway can be caused by overcharging (as a result of the battery’s self-limiting computer failing) or from leaving it in a very hot location. As electricity causes a reaction inside your phone the Lithium batteries warm up and as they warm they expand. Normally this isn’t a problem – manufacturers are aware of heat causing expansion and leave space inside your phone for that expansion to occur safely and include limits to prevent anything that might cause a thermal reaction (like including a battery computer to prevent it from overcharging). When thermal runaway happens the battery expands past the intended limits and cracks its casing, reacts to other parts of your phone, and can catch on fire if it expands out enough to come into contact with air.
See a video of it happening: This person removed the safeguards that prevent a phone battery from overcharging.
Something similar but much faster can happen as a result of a short in the battery. Shorts in the battery can be caused by a leak in the envelope holding the electrolyte gel or by a conductive material accidentally connecting the positive and negative electrodes. Shorts can be caused by mechanical damage (a puncture or tear in the electrolyte envelope) if it causes the electrolyte gel to leak.
See a video of it happening: This person created a short circuit by connecting the negative and positive electrodes on a small battery.
If you have a device with LI batteries, whether it’s a cell phone or a hoverboard, make sure to store it at appropriate temperatures, avoid overcharging it, and take precautions to avoid puncturing or significantly cracking the casing. LI battery explosions are incredibly uncommon, which is why they dominate the news cycle when they do happen. Statistically these batteries are very safe and have a very low failure rate but there are risks that arise as a result of the continuing pursuit of a long-lasting, light-weight battery.