You've probably seen them in the news or read about it online. First it was the Florida man who's electronic cigarette exploded in his face. More recently, stories have emerged about eGo style batteries catching fire or exploding while charging. Rechargeable batteries based on lithium-ion technology are what power many of our electronic devices, not just e-cigarettes. And because of the nature of their chemistry, lithium batteries all possess inherent risks.
Battery technology hasn't changed much over the years, but instead we see the same rechargeable cells packaged differently, shrunken down, and packed in more tightly. This not only creates a more powerful, energy-dense battery, but also a more dangerous one. Electronic cigarettes aren't the only devices susceptible to battery explosions. Laptops and cell phones have also been known to catch fire and even explode with improper use.
A defective or improperly used battery can overheat. This can create quite the mess as its cells will begin to break open before setting off a chain of other cells in the battery to burst. In a process called thermal runaway, lithium batteries may either swell up and/or ultimately explode if prompt action is not taken.
One such inherent danger of lithium batteries is the potential to ignite on fire. Lithium has a very high electrochemical potential and is therefore used in many common batteries. The lithium ion has a low atomic weight, which reduces the mass of lithium batteries. However it produces a ton of energy as it moves toward the electrode, along with a great deal of heat. The smaller the battery, the greater the chance of it overheating.
With e-cigarettes, different devices have different wattage outputs and therefore require specific battery models. Using a battery that's too small for a particular APV increases the risk of it venting, overheating or even exploding.
While lithium is extraordinary for making high-limit electric cells, these same lands make it profoundly reactive and more inclined to warm runaway. Lithium is an Alkali Metal in addition to sodium, potassium, and whatever is left of the first aggregation of the occasional table. These components are profoundly combustible and reactive to the point that hurling a couple of grams into water will make a blast. So when an Li-particle heats up, the lithium in it can quicken the breakdown of different units.
In terms of electronic cigarettes, battery explosions can most commonly be attributed to user error, not a malfunction of the devices themselves.
Make sure to use the proper battery with your device.
Do not leave batteries unattended in automobiles or other places where they may be subjected to high heat.
If you ever hear your battery venting, or making a hissing noise, immediately cease use and remove the battery from the device and set it aside in a safe place until it cools off. Batteries tend to explode under high stress, not just because they are being used in an electronic cigarette. To learn more about battery safety, check out Battery University.