E-Cig Battery Safety – A guide

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Battery Safety:
By M. Olmstead

The recent story of a gentleman in Florida being injured by what what the news is reporting as an exploding electronic cigarette, causing extensive facial trauma, is on the surface alarming.  Journalist types, as is often the case, report just enough information to get the ignorant masses in a tizzy, with sensational media hoopla and dramatic infotainment without much content.  Sensationalism aside, the fact remains we don’t know what event or series of events lead up to this catastrophic failure.  Without knowing more, there really isn’t anymore to say about this incident.  What we can discuss, however, is what we can do, as ecig users to make sure this kind of thing doesn’t happen to us.

 

 

 

Lets talk about batteries, shall we?  First we need a quick lesson in battery terminology.


Cell: Another term for battery.

Voltage: The imprinted voltage on the battery refers to the nominal voltage.

Capacity: Capacity represents the specific energy in ampere-hours (Ah).

Amps: A measure of current (A)

C-Rating: The critical factor for ecig mod use is the C rating (discharge current) in amps. The minimum possible value for safe and effective ecig use is 1 amp (= 1000mA) although ideally it needs to be higher. The ideal rating is 2 amps (2000mA) or higher as an atomizer usually draws 1A to 2A.  The higher the C rating, the higher the maximum discharge current is.(4)

Series:  This term refers to what is often called “stacking batteries.”  This means you are doubling the voltage while maintaining the same capacity rating. This is where a lot of the danger lies as people have been known to use batteries with too low C-rating causing extreme stress on the batteries leading to catastrophic failure.

Parallel: This term refers to when you are doubling the capacity (amp hours) of the battery pack while maintaining the voltage produced by a single cell.  This reduces stress on an individual cell, by spreading the workload over two or more cells.

Internal Resistance: It reduces the battery’s overall charge capacity.  It is the result of cell oxidation, a process that occurs naturally with use and aging.  The older the battery, the higher the internal resistance is.  Battery stress (as often happens with ecigs) speeds up this process.

Battery Stress: In addition to lessening the useful life of the battery, severe stress can cause high heat and over current (should the protection circuit fail) and the battery may vent gases, or worse, even have a “venting with flame” event.

Thermal Runaway: The rapid rise in heat caused in a cell from a short/fault condition that rapidly may lead to a “venting with flame” event.

Venting With Flame: A catastrophic battery failure resulting in an explosion.

Now that we know some of the terms, lets discuss the different types of batteries out there that people put in their mods.

Lithium-ion:
The most common type of battery is the Li-ion.  In very simple terms, there are two types of Li-ion batteries you could put in a MOD.  Protected, and unprotected.

An unprotected cell is just that.  A lithium-ion cell uses a cathode (positive electrode), an anode (negative electrode) and electrolyte as conductor. The cathode is a metal oxide and the anode consists of porous carbon. During discharge, the ions flow from the anode to the cathode through the electrolyte and separator; charging reverses the direction and the ions flow from the cathode to the anode.(1)  A short/fault, either in the battery itself (from a manufacturing defect) or from an atomizer or cartomizer (causing excessive current draw greater than the battery is rated for) will cause a rapid buildup of heat due to the current.  This “thermal runaway,” can rapidly lead to an explosion, or  “venting with flame.”  These batteries are dangerous in MODs that don’t have any sort of internal protection which can detect a short, or excessive heat.

A protected Li-ion cell has safety at multiple levels depending on the manufacturer.  The safety begins with the battery cell, which includes: [1] a built-in temperature switch called PTC that protects against high current surges, [2] a circuit interrupt device (CID) that opens the electrical path if an over-charge raises the internal cell pressure to 1000 kPa (145psi), and [3]a safety vent that releases gas in the event of a rapid increase in cell pressure.  In addition to these internal safeguards, an external electronic protection circuit prevents the charge voltage of any cell from exceeding 4.30V. Furthermore, a fuse cuts the current if the skin temperature of any cell approaches 90°C (194°F). To prevent the battery from over-discharging, a control circuit cuts off the current path at about 2.20V/cell.  Protection circuits can only shield abuse from the outside, such as an electrical short or faulty charger. If, however, a defect occurs within the cell, such as contamination caused by microscopic metal particles, the external protection circuit has little effect and cannot arrest the reaction.(2)

Safe Chemistry Batteries:
Lithium-ion batteries require a protection circuit for safety, whereas Lithium iron phosphate (LiFePO4) and Lithium Manganese (LiMn or IMR) use safe chemistry. Although these batteries utilize a safer chemistry, protection circuits in the MOD itself are generally recommended. The safer chemistry will prevent venting with flames in the event of a catastrophic failure.  Lithium-ion batteries contain an oxidizer, which produces its own oxygen to support combustion, should sufficient heat be available from a short circuit.(3)

Lithium Iron Phosphate (LiFePO4):
Lithium iron phosphate batteries have a safe chemistry. Li-FePO4 is a newer technology and more expensive than Li-ion. This is a safe technology and they don’t need any protection.  Benefits include longer service life (1000 charge cycles), no battery memory, and fast recharging.  Make sure you get high quality Li-FePO4’s with a high C-rating.  A C-rating of at least 4C is needed to power an atomizer effectively.  Please note that you will need a special charger for this type of battery.  The nominal voltage of a standard Li-ion battery is 3.6-3.7v with a maximum charge voltage of 4.2v.  The nominal working voltage of the Li-FePO4 is 3.0-3.3v with a max charge voltage of 3.6v.  Never place a 3v battery in a 3.7v charger.  Li-FePO4 batteries can be “stacked” in series, but no more than 2 is recommended, and do not use them in parallel.(4)

Lithium Manganese (LiMn or IMR):
These batteries are considered a safe chemistry, and unlikely to explode during use. They are recommended in place of Li-ions and do not need a protection circuit.  They have no memory effect, and tend to not last as long as their Li-ion counterparts due to the higher C-rating.  Low internal resistance is key to fast charging and high-current discharging. In an 18650 battery, Li-Mn can be discharged at currents of 20–30A with moderate heat buildup.(5)  Care should be taken to only use a newer technology charger.  Due to the low internal resistance, older chargers can over charge IMR’s resulting in decreased lifespan, or even cause them to burst.  Also take care to not discharge them below 3.5v as that will shorten useful life as well.(3,4)


Simple Guidelines for Using Rechargeable Batteries

Use only the type of battery (chemistry, size, and C-rating) recommended by the MOD manufacturer. Don’t buy cheap, no name batteries, only buy them from reputable manufacturers and vendors.

Exercise caution when handling and testing lithium-ion batteries. Test your batteries and charger periodically using a multi-meter.  Do not short-circuit, overcharge, crush, drop, mutilate, penetrate with foreign objects, apply reverse polarity, expose to high temperature or disassemble packs and cells.  Do not use the battery if the outer wrapper is damaged.

Use only lithium-ion cells with a designated protection circuit and approved charger, or better yet, use only high quality safe chemistry batteries.

Make sure the charger is the appropriate voltage for the battery you are charging.  High temperature during charge or discharge may hint of pending failure, discontinue using the battery and/or charger. The electrolyte is highly flammable and battery rupture can cause physical injury.

Use a foam extinguisher, CO2, dry chemical, powdered graphite, copper powder or soda(sodium carbonate) to extinguish a lithium-ion fire. Only pour water to prevent the fire from spreading.  If the fire of a burning lithium-ion battery cannot be extinguished, allow the pack to burn out on its own in a controlled and safe way.(2)

Also note: the bigger the battery, the safer the battery.

The larger the battery, the greater the safety margin.  Demanding too much current from small cells that can’t provide it, can lead to catastrophic thermal runaway.  Stacking cells (such as low C-rated RCR123’s) can place extreme stress and lead to failure. If your MOD requires stacked batteries, make sure you use high quality cells with a high C-rating.  The best practice to use a MOD with built in protection (thermal and current) to ensure maximum safety.  Also ensure that all metal mods have venting or a blowout plug to vent expanding gases in the event of thermal runaway.  This venting may not keep your mod from exploding, but it should give you a good indication that something is very wrong, hopefully allowing you enough time to get out of harms way.

For reference, here is a chart of C-ratings vs size for different batteries.(4)

1C or less for low-quality Li-FePO4

Assume 1C for generic Li-ion unless otherwise noted

1.5C for ultra/sure/trust/-fire Li-ion

2C for AW ICR (Li-ion)

3C for BDL 10440 IMR (Li-Mn)

5C for BDL 14500 IMR (Li-Mn)

8C for AW 14500 and 16340 IMR (Li-Mn)

10C for AW 18650 IMR (Li-Mn)

10C for AW LiFePo4

General consensus is that AW brand batteries are regarded as the best and safest for use in an ecig MOD.  As always, use the battery and charger recommended by the MOD manufacturer for best results.

Periodically check the voltage of your batteries with a multimeter to ensure they aren’t overcharging.  Don’t have a multi-meter?  Get one.  It is an invaluable tool that every vaper should own.

In summary, handling and using a device that houses a rechargeable battery, carries with it a certain level of risk, be it a computer, electric razor, electric toothbrush, cell phone, or our beloved ecigs.  Risk can be managed and minimized with knowledge of safe practices, not skimping on quality, periodic monitoring and inspection of your equipment, and most importantly, remaining diligent.

When in doubt, throw it out.

 

Bibliography:

1 – http://batteryuniversity.com/learn/article/lithium_based_batteries

2 – http://batteryuniversity.com/learn/article/safety_circuits_for_modern_batteries

3 – http://www.happyvaper.com/Articles.asp?ID=240

4 – http://www.e-cigarette-forum.com/forum/ecf-library/129569-rechargeable-batteries.html

5 – http://batteryuniversity.com/learn/article/types_of_lithium_ion

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