Introduction to Battery Safety

Special thanks to Mooch for this information.  This information was all culled from Mooch's facebook page and posts at ECF.   Mooch is a community supporter who has been doing battery tests for a long time and helping the vaping community make sense of the safe usage of battery cells used in vaping.  Here is a link to his battery tests and methods of testing.

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The first thing you need to know, is there are no batteries used by vapers that have a continuous rating above 30A.  Despite many battery wrappings suggesting they do.

There are no 18650 batteries used by vapers with a capacity above 3000mAh that have a continuous rating above 10A.  Despite many battery wrappings suggesting they do.

It is my personal opinion that it is a good practice to avoid those companies that choose to exaggerate their specs to increase sales.   For instance, would you buy a cheeseburger from a guy who was caught selling rat-meat in his chicken burgers?  Neither would we.

LG, Samsung, and Sony are the only high drain IMR 18650 cells we will carry until we can find one from a manufacturer that supports >30A through testing, not exaggerated specifications. 

A battery capability is not a battery rating!

• Just because a battery can be vaped with at 40A, and not vaporize your face, does not mean it's a 40A battery.  (Even if it seems to be performing great.)
• Just as importantly... a battery rating does not limit or define a battery's capabilities!
• If a battery is given a 20A rating that does not mean it cannot be vaped with at 40A.

We are going to outline some of the differences in the safety of the chemistry used in our batteries.

The Battery Bro website has a fantastic explanation of the different chemistries themselves, if you can't wait til the end of the article, or want more detailed information you can click here.

Before we go into the chemistry safety differences lets define the two different events that can occur if the battery is abused too hard; venting and thermal runaway.

-- Venting --

Venting is a purely physical process that releases excess pressure that forms inside a battery if it is discharged too quickly or charged at too high a voltage. Both of these situations cause excess gas to be created and that increases the pressure inside the battery.

Venting is completely different from thermal runaway, which is covered next.

Each battery has a pre-weakened area of metal underneath the top contact. At a certain pressure level the weakened metal splits open and allows the pressure to escape. The solvent for the battery's electrolyte often oozes or sprays out too. This can be a problem because not only is it toxic but venting typically happens at around 130°C-160°C, which means the liquid is very, very hot.

Venting can be a rather gentle event or it can be a pretty energetic spurting and spraying of gas and liquid. Be careful, that liquid is toxic and flammable!   The battery does not burst and there are no sparks or flames.  The amount of gas produced is relatively small and can usually be handled quite easily by the venting holes we see in mods.

Once a battery vents, even just a little, it is ruined and should never be used again.

Thermal Runaway

This is a catastrophic failure due to uncontrolled chemical reactions inside the battery. It always results in the bursting of the battery, sometimes quite violently, and can be accompanied by sparks and flames.

As the temperature of the battery rises during a discharge, certain exothermic chemical reactions can start as the temperature goes above about 75°C. This is the beginning of the process that can lead to thermal runaway if these reactions are not stopped.
If not being discharged too quickly, or the battery is being cooled a bit by ambient air flow or a metal mechanical mod tube, these new reactions can stabilize at a certain rate and not continue to increase the battery temperature. If the discharge current level is too high, or there's no cooling, then these reactions keep increasing the temperature of the battery. This causes more exothermic reactions to begin, which heats up the battery even more, which causes even more reactions to begin, and so on.

As the battery reaches about 125°C the plastic sheet (the "separator") between the two sides of the battery, positive and negative, begins to melt. This can lead to small short circuits forming at different points in the battery. These short circuits increase the temperature at those points, further increasing the rate that the battery temperature rises.

As the temperature continues to rise certain compounds start decomposing and releasing large amounts of gas. This increases the pressure inside the battery and, hopefully, leads to venting of the battery to release the pressure. But if the temperature and pressure buildup happens quickly enough, the battery won't vent in time.

At about 230°C - 270°C the thermal runaway threshold temperature is reached. This is where there the materials inside the battery are decomposing incredibly fast. There is a huge buildup of gas and the battery bursts open, often ejecting its contents and throwing pieces of battery a long distance. Depending on the threshold temperature the solvent can also ignite, resulting in a fireball to accompany the shrapnel.

While it can be quite violent, this isn't the explosion seen in a few videos that have made their way through the vaping groups and forums. Those explosions happen when a device doesn't have a pop off side panel or large open areas for the pressure to escape. The device holds back the gases for a bit but eventually it can't withstand the increasing pressure and it explodes.

It is quite difficult, but not impossible, to bring the temperature of a battery up quickly enough to go into thermal runaway without it venting first. About the only way to do it is with a short circuit.

Both venting and thermal runaway can take hours to occur or they can happen very quickly. You will typically be able to feel a battery getting hot before it vents but do not assume the same for preventing thermal runaway. That depends on a very, very fast rise in temperature, happening before the battery can vent. You might not feel the battery get hot first.

How do we prevent thermal runaway then?

• Never allow your batteries to be short circuited!
• Keep your battery wraps and top insulating rings in perfect condition, replacing them when necessary.
• Never use an atomizer with a press-fit or spring-loaded 510 pin on a hybrid top mechanical mod.  Always make sure that the 510 pin sticks out past the threaded stem of the atomizer and is not floating.  Floating means if you remove the atomizer coil, you should not be able to move the 510 positive pin (in or out or wiggle) without a screwdriver.
• Absolutely NEVER put a battery in your pocket unless it's in a case.  Best practice is to never have a battery loose.  If your battery is only in a case, mod or charger, you will greatly reduce the possibility of an incident.
• If you put your mod in your pocket or purse, turn it off. Make sure the battery cover is secure, or in the case of mechanical mod - remove the batteries and put them in a case.

Li-Ion Battery Chemistries - What are the differences in their safety?

Differences in Battery Chemistry Safety

Each chemistry has different characteristics that make it safer or less safe than another.

The attached table makes some basic comparisons between their safety.  

As the table outlines,

• ICR is the least safe,
• INR is safer, and
• IMR is the safest of the three.

IFR batteries (lithium-ferrous-phosphate), like the ones from A123 , are the safest Li-Ion chemistry. Their lower nominal voltage, 3.3V versus 3.6V-3.7V, causes problems for regulated devices though.  They reach the "low battery" point much faster than the other higher voltage chemistries.

The term "IMR" is being used by some battery companies as a generic term for any of their batteries that aren't ICR. These "IMR" batteries can be true IMR chemistry or one of the hybrid INR chemistries.

While not accurate this isn't a safety issue as both IMR and INR are the safer chemistries.Not safe...safer.   Any battery can be unsafe if abused enough.  

ICR batteries are not recommended unless you are very familiar with your device, Ohm's Law, and battery safety. The consequences of abusing these batteries is much, much worse than with INR and IMR.

-- Conclusion --

This can all sound quite ominous, making every battery sound like a bomb waiting to blow.   While Li-Ion batteries can be dangerous if abused, we shouldn't fear them.   A little knowledge and respect goes a long way towards making sure we never have problems.  

Know your batteries and vape safe!

 Special Thanks to Mooch for the information and charts.  You can keep up with Mooch's work in battery testing from his blog at ECF or following his page on Facebook.