BU-304a: Safety Concerns with Li-ion

Learn what causes Li-ion to fail and what to do in case of fire.

Modern batteries contain highly reactive chemicals that will react at elevated temperature by default. The objective is to operate in a stable environmental bandwidth. 

Safety is a sensitive issue that gets much media and legal attention, especially with Li-ion batteries. Any energy storage device carries a risk, and in the 1800s steam engines exploded and people got hurt. Carrying highly flammable gasoline in cars was a hot topic in the early 1900s. Battery makers are obligated to meet safety requirements, but less reputable firms may cheat — it’s “buyers be beware!” Most OEMs use only Li-ion batteries that comply with one or several safety standards. [BU-207 Safety Concerns with Li-ion, UL1642] 

Lithium-ion is safe but with millions of consumers using batteries, failures are bound to happen. In 2006, a one-in-200,000 breakdown triggered a recall of almost six million lithium-ion packs. Sony, the maker of the lithium-ion cells in question, points out that on rare occasions microscopic metal particles may come into contact with other parts of the battery cell, leading to a short circuit within the cell.

Battery manufacturers strive to minimize the presence of such particles; however, complex assembly techniques make the elimination of all metallic dust a challenge. Cells with ultra-thin separators of 24µm or less are more susceptible to impurities than the older designs with lower Ah ratings. Whereas the 1,350mAh cell in the 18650 package could tolerate the nail penetration test, the high-density 3,400mAh can ignite when performing the same test. New safety standards are more relevant to how batteries are used and the UL1642 Underwriters Laboratories (UL) test no longer mandates nail penetration for safety acceptance of lithium-based batteries.

Li-ion using conventional metal oxides is nearing its theoretical limit on specific energy. Rather than optimizing capacity, battery makers are improving manufacturing methods to enhance safety and increase the calendar life. The real problem lies in rare occasions when an electrical short develops inside the cell. The external protection peripherals in such a case are ineffective to stop the thermal runaway when in progress. The batteries recalled in 2006 had passed the UL safety requirements — yet they failed under normal use.

Let’s examine the inner workings of the cell closer. A mild short will only cause elevated self-discharge and the heat buildup is minimal because the discharging power is very low. If enough microscopic metallic particles converge on one spot, a sizable current begins to flow between the electrodes of the cell and the spot heats up and weakens. As a small water leak in a faulty hydro dam can develop to a torrent and take a structure down, so also can heat buildup damage the insulation layer in a cell and cause an electrical short. The temperature can quickly reach 500C (932F), at which point the cell catches fire or it explodes. This thermal runaway that occurs is known as “venting with flame.” “Rapid disassembly” is the preferred term by the battery industry.

Uneven separators can also trigger cell failure. Poor conductivity due to dry area increases the resistance, which can generate local heat spots that weaken the integrity of the separator. Heat is always an enemy of the battery.

What to do when a battery overheats . . .

If the battery overheats, hisses or bulges, immediately move the device away from flammable materials and place it to a non-combustible surface. If at all possible, put a disintegrating device outdoors and let it burn out. If the fire occurs in an airplane, the FAA instructs flight attendants not to use fire extinguishers but the use of water or pop soda. Water cools the adjacent material and prevents the fire from spreading. Many research laboratories and factories also use water to put out battery fires. Allow good ventilation while the battery burns itself out. Li-ion contains no lithium metal and does not react with water (lithium metal batteries requires different extinguishing methods).

During a thermal runaway, the high heat of the failing cell may propagate to the next cells, causing them to become thermally unstable also. A chain reaction can occur in which each cell disintegrates on its own timetable. A pack can thus be destroyed in a few seconds or over several hours as each cell is being consumed. To increase safety, packs should include dividers to protect the failing cell from spreading to the neighboring one. Figure 1 shows a laptop that was damaged by a faulty Li-ion battery.

Suspected Li-ion battery destroys laptop


Figure 1: Suspected Li-ion battery destroys laptop

The owner says the laptop popped, hissed, sizzled and began filling the room with smoke.

Courtesy of Shmuel De-Leon

The gas released by venting of a Li-ion cell as part of pressure buildup is mainly carbon dioxide (CO2). Other gases that form through abusive heating are vaporized electrolyte consisting of ethylene and/or propylene. Burning gases include combustion products of the organic solvents.

While lithium-based batteries are heavily scrutinized for safety, nickel- and lead-based batteries also cause fires and are being recalled. The reasons are faulty separators resulting from aging, rough handling, excessive vibration and high-temperature. Lithium-ion batteries have become very safe and heat-related failures occur rarely under correct use.

Last Updated 2/20/2015

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On November 3, 2011 at 4:50am
JasonsRobot  wrote:

Lithium0ion batteries are safest just because their manufacturing process and techniques are truly based of professional use. Its hardly you hear of any heat failure of it. batteries promise long life time come with high percentage of energy failure.

On January 16, 2013 at 2:58am
antoinecoca wrote:

Would anyone know which certifications and norms the Li-Ion battery must comply with when imported in Europe?

On October 28, 2013 at 4:04am
Maria wrote:


I would like to know if someone has data about how hot could a Lithium ion battery culd actually burn? (for large scale fires).

Tks in advanced.

On May 28, 2014 at 10:10am
Louis wrote:

Can I charge Li-ION 4500mAh 3.7V Battery with my “regular” Ni-Cd / Ni-MH RadioShack charger, if so what setting works the best, if any.


On July 19, 2014 at 8:07pm
Brendon wrote:

@Louis:  Definitely not!  Li-Ion is a very different chemistry from NiCd ard NiMH.  Each chemistry requires the use of a charger specifically designed for it.

On July 31, 2014 at 4:43am
j wrote:

We have a lithium fire extinguisher at work… how does it do it? DHL will send batteries by air somehow… there needs to be a way to send batteries safely…

On September 22, 2014 at 8:29pm
BB wrote:

someone played a joke on me by putting a lithium ion battery for a power tool in my oven.  I didn’t know and preheated my oven to 450 degrees before I smelled the plastic melting and discovered it.  How dangerous was this?  Could it have exploded and injured me??

On November 4, 2014 at 8:07am
Dan wrote:

@BB: You should immediately cease contact with that individual and surround yourself with more intelligent beings.

On December 2, 2014 at 2:12pm
Pillow wrote:

I recently got myself Gameboy advance SP and it has Lithium Ion battery. Since it did not come with charger, my dad tried to charge it with home-made charger, he crafted it using old nokia phone charger. Soon, when I was alone home, I discovered that the battery was a bit bigger than before and it was pretty hot. I unplugged it inmediatly and my dad said that he will see if he can charge it on safer way. I would like to ask, should I get the new battery? Is using the same battery dangerous even if it goes back to its normal size? What should I do?

On December 31, 2014 at 9:21am
sp00zer wrote:

Get a new battery right away. Changing physical size is an indication of internal chemical change in the direction of failure. A battery like that should never be reused inside of a device.

On February 18, 2015 at 12:48am
Thomas wrote:

I’m constantly bing told that water is the way to extinguish Li ion fires. And yet fire suppression companies sell class D extinguishers and say that water is NOT the way to fight these fires. What are the facts?

On February 26, 2015 at 10:36pm
Richard A. wrote:

I work for a company that exchanges fire extinguishers in buildings. There is a battery test lab for an automaker that I am iffy about the right extinguishers. They want an ABC, but wouldn’t a Dry Chem Sodium BiCarb be better due to the corrosive factors?

On March 23, 2015 at 3:33pm
Rich wrote:

For primary cells with Lithium, absolutely do no use water. The lithium will react with the water and you will have even more of an issue on your hands. So 1 use coin cells and the like, Class D extinguisher.

For Secondary cells, especially ones that are part of a pack.Put out the flame with pretty much any of the listed extinguishers above then you want to use water and a lot of it. The amount of lithium in secondary Li-Poly and Li-Ion cells is quite low and won’t react. Your goal with the water is want to drop the temp of the surrounding batteries so they don’t overheat and vent.