Although lithium batteries are generally very safe, they occasionally catch fire or explode. When that happens, such as Samsung's Galaxy Note 7 crash, or HP's recent laptop recall, it's always big news. So what's the matter? Why does the battery sometimes explode with a bang? Let's explore.
Rechargeable lithium batteries -- widely used in laptops, mobile phones, tablets, and almost all modern devices you own, as well as electric cars and airplanes -- are an important part of supporting the development of portable devices. Without lithium batteries, I might not be able to write this article in a coffee shop unless I keep my computer plugged into a power outlet.
What is inside a lithium battery?
To understand why lithium batteries sometimes fail, you need to know what's going on under the lid. In each lithium battery, there are two electrodes - a positive cathode and a negative anode - separated by a thin layer of "micro-plastic" so that the two electrodes can not be contacted. When lithium batteries are charged, lithium ions reach the anode from the cathode through the micropore of the separator and conductive fluid. When the battery discharges, the opposite happens when lithium ion flows from the anode to the cathode. This is the response to power the laptop.
Small batteries, such as those in smartphones, usually have only one lithium-ion battery. Larger batteries, such as laptops, typically have six to twelve lithium-ion batteries. Batteries on electric cars and aircraft can have hundreds of batteries
What makes lithium batteries explode?
Things that make lithium batteries so useful also enable them to ignite or explode. Lithium is excellent at storing energy. When it is released as a trickle, it will power your phone for a whole day. But when it is released all at once, the battery explodes.
Most lithium batteries fire and explode due to short circuit. This happens when the plastic separator fails, so that the anode and cathode are in direct contact. Once the two poles get together, the battery starts to overheat.
There are many reasons why the separator may fail:
1. Bad design or manufacturing defects: Batteries are poorly designed, just like Galaxy Note7. In this case, there is not enough room for electrodes and separators in the battery. In some models, when the battery is charged, the electrodes bend and cause a short circuit. Even designed batteries can explode if quality control is not strict enough or faulty manufacturing.
2. External factors: Extreme high temperature will definitely cause separator failure. Batteries that are too close to the source of fire or in the middle of a fire can cause the battery to explode. Other external factors can also lead to lithium battery failure. If the cell phone is smashed hard (or several times), it may damage the separator and lead to contact of the electrodes. If you pierce the battery (accidentally or intentionally), it will almost certainly cause a short circuit.
3. Charger problem: Charger with poor quality or insulation will also damage lithium batteries. If the charger is short-circuited or generates heat near the battery, it can cause enough damage to cause failure. That's why we recommend using only official chargers (or at least high-quality third-party chargers from reputable brands).
4. Thermal runaway and multi-battery: Although not related to the single battery found in most smartphones (the iPhone X actually has two batteries), only the second one will start after the battery unit fails. Once a lithium battery overheats, a domino effect called thermal runaway occurs. "For batteries with hundreds of batteries like Tesla Models, this can be a very big problem.
Although lithium batteries sometimes fail, they are still a safe and mature technology. That's why when the battery suddenly explodes, it becomes news, and it shows how rare major failures are. Battery manufacturers have installed a large number of protective measures to prevent battery failure, or at least to mitigate the damage caused by the failure.