By Tom Pruen
About Lithium-ion batteries
The batteries in electronic cigarettes have a chemistry that is known as Lithium-ion (Li-ion). Li-ion batteries offer extremely high energy density (they store a lot of power in a small space), which is why they have been adopted for use in small, power-hungry devices such as mobile phones, laptops and electronic cigarettes. The high energy density enables a small battery to provide a useful amount of power, but if something causes the battery to fail in a way that releases this power quickly, the results can be dramatic, and dangerous. This has been seen in rare cases with pretty much every device that uses a Li-ion battery. Li-ion batteries are most vulnerable to failure during charging, as this is when the energy density is highest, and there is an increased risk of an inappropriate voltage being applied to the battery.
Despite the dramatic nature of the way in which Lithium-ion batteries fail, they are generally very safe. Most of us own a cell phone or laptop, or indeed both, but have never experienced any issues. Similarly, there are literally millions of e-cig batteries in use, and incidents of this nature are few and far between.
Why do batteries fail?
The main causes of battery failure (aside from physical damage), are electrical shorts, wrong charging voltage or current, and thermal runaway.
Incorrect charging power is almost always the result of using the wrong charger, or power supply. The USB specification is for maximum current of 500mA, but many power supplies extend this to 1000 or more mA, for devices such as iPads. A variety of chargers and batteries are on the market, with some chargers containing the charge control circuits to control power supply and prevent overcharging, while some have this contained in the battery. Mixing chargers, therefore, runs the risk of omitting the control circuitry completely, resulting in either too high a voltage, or too high a current being supplied to the Li-ion cell. There is also then the potential for overcharging, as continuing to try and fill an already full battery will, not surprisingly, damage it.
Electrical shorts are usually a result of damage to the connector where the atomiser and charger screw in. The positive and negative poles are separated by an insulator, and this can be physically damaged, usually by over-tightening the screw fitting. If the connector is damaged, this effectively attempts to empty all the power of the battery back into the battery, causing thermal runaway.
Thermal runaway in use is usually a result of a manufacturing defect in the battery which causes an internal chemical reaction in the battery, which once started leads to an ongoing reaction which destroys the battery. This is rare, but to avoid this, you should buy batteries from a reputable vendor who has invested in quality control. It is also caused by both electrical shorts and overcharging. Physically heating a battery also significantly increases the risk of failure, and while this may seem unlikely, it’s worth bearing in mind for the summer sun.
So how can the risks be minimised?
Always buy batteries from a reputable vendor. We would particularly recommend using ECITA members’ products because this offers the reassurance that all the safety testing and compliance documentation is in place and has been checked.
Never over-tighten either atomiser or charger into the battery. Screw things in until they work, and then stop; never screw in until it is as tight as you can make it.
Always use the charger that matches the battery (don’t mix and match chargers and batteries from different brands or models)
Always use a standard (500mA) USB power supply
Do not leave batteries charging unattended! (It’s always better to be safe than sorry.)
Never leave batteries in your car (especially with good weather being on the way, hopefully)
Keep dry. (Obvious, but important!)
Check that the contacts are free of e-liquid and clean with a cotton bud or tissue if needed (added thanks to the very valid comment from Mike)
As an extra layer of safety, there are products available to place batteries in while charging (usually called Li-po bags). These are intended to contain any failure of the battery while charging, but should not be used as a substitute for all of the advice above!