Li-Ion protection technology and possible dangers

[NewBie]

If I get time, I will try to write-up more tonight.

 

[NextLight]

Newbie,

Thanks for your excellent input. Most EEs I work with think of me as a battery expert (I joke "more ex-spurt, as in former drip under pressure") but I am feeling like a beginner again. I like that!

Questions.

(1) I thought ALL Li-Ions had built-in PTC protection, but I am hearing there may be bare metal Asian Li-Ions without PTC, fuse, or bi-metallic resettable over temp switch. Which is true in your experience?

(2) Cutting off the PCB from a popular Asian protected AA 14500, and then shorting the bare cell, I am pretty sure I see over 18 amps in a 2 second test. Aside from the obvious extreme danger of shorting a Li-Ion, doesn't this suggest the raw cell is completely unprotected?

(3) If we buy a protected cell, we usually know the current limit of the protected cell ASSEMBLY (with a PCA on the bottom or top of the cell.) How do we trace back to the manufacturer, to determine if the cell is approved for 2.5C?

TIA,
David

 

[NewBie]

Newbie,

Thanks for your excellent input. Most EEs I work with think of me as a battery expert (I joke "more ex-spurt, as in former drip under pressure") but I am feeling like a beginner again. I like that!

Questions.

(1) I thought ALL Li-Ions had built-in PTC protection, but I am hearing there may be bare metal Asian Li-Ions without PTC, fuse, or bi-metallic resettable over temp switch. Which is true in your experience?

I've seen cells without most of the protection devices, short the separator, which is required to make the cell anyhow...and venting mechanism. Most of these are of the type where you have to weld on your own connections, but not all. It is easy to make things that appear the same on the outside. This is why one should be careful as to where you get your cells from. Usually bare cells are only available to qualified manufacturers who know what they are doing, and are designed to be built into battery packs, with a whole host of protection mechanisms as mentioned earlier in this thread.

(2) Cutting off the PCB from a popular Asian protected AA 14500, and then shorting the bare cell, I am pretty sure I see over 18 amps in a 2 second test. Aside from the obvious extreme danger of shorting a Li-Ion, doesn't this suggest the raw cell is completely unprotected?

It very well could be that the "mechanical/chemical/thermal" are not present, and the cell is only protected by the electronics on that board. Personally, I'd consider that less safe. There is a good chance these are lower in cost than normal. It sounds like the bare cell in your example is completely unprotected. This is bothersome, when one thinks about it, as electronics do fail, and at low cost margins, manufacturers will even skip ESD protection on the electronics. Just a static zap could render the electronics dead, and the MOSFET can easily be blown in the shorted state. At that point, you would be running completely unprotected, which is very dangerous.

(3) If we buy a protected cell, we usually know the current limit of the protected cell ASSEMBLY (with a PCA on the bottom or top of the cell.) How do we trace back to the manufacturer, to determine if the cell is approved for 2.5C?

TIA,
David

The folks whom you bought it from should provide all the details. This information should be found on the datasheet/product specification sheet. Did you know that some Li-Ion cells are not even rated for 2C discharges? As far as the information you get, so you must place your faith in the cell distributor. Usually, there are also various agency approvals, such as UL, and one can go to these places to see under what conditions things were tested. UL has several tests that are performed. An example is UL1642, which many people consider the safe minium test for cells:

-Abnormal Charge Test
Test method : Cells are discharged per 6.2, then charged at constant current of 7200mA and constant voltage of 4.2V while tapering the charge current. Charging is continued for 48 hours (Per UL1642).

-External Short-circuiting Test
Test method : Cells are charged per 6.1, and the positive and negative terminal is connected by a 100m Ω-wire for 1 hour (Per UL1642).

-Overdischarge Test
Test method : Cells are discharged at constant current of 480mA to 250% of the minimum capacity (Per UL1642).

There are many more tests required under UL1642.

Just because something passes UL1642, it is good to know to what level.
Level 0 No Change
Level 1 Leak
Level 2 Smoke < 200 degrees C
Level 3 Smoke > 200 degrees C
Level 4 Fire
Level 5 Explosion

Not all Li-Ion cells are created the same, either. There are various electrolyte additives, and other things manufactures do to their cells, which make them much more safe. Usually, when you find something cheap, you are getting something cheap. A lot of cells will not pass UL1642, especially stuff that folks will purchase direct out of Asia, that often also do not carry proper documentation.

I still had an old datasheet sitting on my hard drive for one of the types of safer LG Chem cells that they offer, the ICR18650. In it, notice they just list no rupture, no fire, but this doesn't mention no smoke, superheated or not.
http://www.molalla.net/~leeper/18650a3.pdf

At the end of the datasheet, notice this is a unprotected, not bare cell. You can see the positive end cap on it.


Another neat thing I have kicking around on my drive is some testing that was done on the Sony cells. It shows the rapid degradation of Li-Ion cells when ran at 45C and 55C.

LiIon capacity fade over time(cycles) when ran at various temperatures:
http://www.che.sc.edu/faculty/popov/drbnp/Ramadass/SLCCapacityFade.ppt


Remember, I'm definitely no expert on the subject, I just know a little bit.


.

 

[BentHeadTX]

I love my NiMH batteries!
Still use my nads and don't want a pocket flashlight bomb taking them off. We were testing a Milwaukee 28V 3.0AH Lithium-Ion pack on the Cadex analyzer and after an hour, there was a crackling sound the the Cadex went nuts and started alarming. The battery is now dead and will be heading back to Milwaukee (they cost $129 a piece) Not sure who makes those things but they charge very fast and dump over 60 amps when called upon.
Although it would be fun to see what happens to the battery when a bullet goes though it, we will send it back for exchange.
I was thinking of lithium-ion rechargables for my Mediterranean but went with a 2AA NiMH battery pack instead. My 1.7 watt NiMH single AA fed MillerMods L1P should be arriving in a few days so I can have small, bright and safe in one light that is rechargable. I knew that lithium-ion can be dangerous but now I know by how much.
Maybe when Valence and A123 System lithium-ion RCR123A batteries become available I'll move to them. For now, NiMH and the occasional primary lithium AAA for my keychain light works great. Thanks for the information and your service to CPF'ers to keep us safe.

 

[HighLight]

Quick question. I use an unprotected RCR2 li-ion in an Orb Raw with 3w luxeon emitter. I charge this cell in a small NanoCharger. It say 310ma on the cell.
Do I have to concern myself with anything that is written here?

 

[NewBie]

I love my NiMH batteries!
Still use my nads and don't want a pocket flashlight bomb taking them off. We were testing a Milwaukee 28V 3.0AH Lithium-Ion pack on the Cadex analyzer and after an hour, there was a crackling sound the the Cadex went nuts and started alarming. The battery is now dead and will be heading back to Milwaukee (they cost $129 a piece) Not sure who makes those things but they charge very fast and dump over 60 amps when called upon.

I once remember reading something about Sony Li-Ion and Milwalkee. Sony makes some very special cells for tool purposes, which are quite different than their normal 18650G8 2550mAH cells (the G8 have over twice cell power density at 545WH/L):

Main Specifications of High-Power Output Cylindrical Lithium Ion Battery»
Cell Type 18650V
Size diameter:18mm, height:65mm
Capacity (0.2CmA) 1600mAh
Standard Charging Voltage 4.2V-2.5V
Energy Density 250Wh/L
Max. Output 10 Amps
Weight 44g

Cell Type 26650VT
Size diameter: 26mm, height:65mm
Capacity (0.2CmA): 2500mAh
Standard Charging Voltage: 4.1V-2.5V
Energy Density: 250Wh/L
Max. Output: 50 Amps
Weight: 90g

High power Cylindrical Lithium Ion battery (V Cell, VT Cell Series)
By using Nickel/Manganese mixture in the positive electrode, stability in high temperature conditions have been achieved, also achieving safe usage with high level of current, this being the characteristics of V/VT series. By the combination with high-voltage, which is the characteristics of lithium ion batteries, usage in the high-power output application field (such as power tools, cleaners, motor assisted bicycles) will be ideal, where conventionally Nickel-Cadmium, Nickel-Hydrogen batteries were used. In the 18650V cell, maximum output of 10A, and in the 6650VT cell, maximum output of 50A have been achieved.


I also see that Molicel brokered a deal with Milwaukee:
"Molicel® has been a recognized industry leader in the research & development of manganese based lithium-ion cells for the past decade. Using lithium manganese oxide (LiMn2O4) in the positive electrode of the new IMR26700 cell allows .... currents in excess of 100A.

By eliminating cobalt from the IMR26700 cell ... while providing exceptional safety characteristics. Further developments of the IMR26700 cell will provide fast charge capability, allowing cells to be fully charged in as little as 15 minutes."
http://www.molienergy.com/Press Releases/release040117.htm

Then there are the special Toshiba Li-Ion cells from early last year, that are rapid charge, which use a nanotechnology in them:
http://www.toshiba.co.jp/about/press/2005_03/pr2901.htm

Panasonic recommends charge rates of 0.7C for their cells, and if below 2.9V on the discharge, then 0.1C. They also don't like you discharging their cells below 3.0V. They only recommend discharging their cells at 1.0C. And they do not want you to discharge their cells at temperatures above 60 degrees C.
http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_LiIon_Precautions.pdf
http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_LiIon_Charging.pdf

Molicel specifies a maximum discharge rate of 1.67 C, a discharge voltage cut-off of 2.5V, and a maximum discharge temp of 60 degrees C:
http://www.molienergy.com/specs/ICR-18650J.pdf

Varta specifies a maximum discharge rate of 2.0C (4800mA), a discharge voltage cut-off of 2.75V, and a maximum discharge temperature of 60 degrees C, and even carry the UL1642 rating, but they don't specify to what level the comply. (keep in mind, their older cell is not rated at the 2.0C discharge rate)
http://www.varta-microbattery.com/en/mb_data/documents/data_sheets/DS56624.pdf


Don't care about treating these things safe?
" Curtis Sathre said it was like a bomb going off. His 13-year-old son Michael stood stunned, his ears ringing, hand gushing blood and body covered in black ash. In a split second last August, fragments from Michael's exploding cell phone had hit him between the eyes and lodged in the ceiling of the family's home in Oceanside, Calif." WASHINGTON (AP), 2004

You can bet that cell phone makers are using quite a few techinques in an attempt to keep these things from turning into bombs.

"The CPSC is trying to determine if improved venting is enough by itself to ensure safety. "We have seen temperatures as high as 600 degrees, and you can have a torch-like effect if these batteries don't function properly," Wolfson said. "

Folks have attempted to bury the issue by saying these issues are caused by aftermarket cells, but let me assure you, there have been quite a few cases where these things go off with the original factory cells.

Companies who know what they are doing, have been the subject of Li-Ion cell recalls, and there have been a whole multitude of cases listed which include cells exploding, bursting, fire:

Black Diamond, Soliras Headlamp Li-Ion Batteries, http://www.cpsc.gov/CPSCPUB/PREREL/prhtml05/05043.html

Apple (2004), PowerBook G4 and iBook G4, Battery Manufacturer: LG Chem Ltd., http://www.cpsc.gov/CPSCPUB/PREREL/prhtml04/04201.html

EV Global Motors, Mini E-Bike electric bicycles, http://www.cpsc.gov/CPSCPUB/PREREL/prhtml02/02251.html

Thomson, DVD player, http://www.cpsc.gov/CPSCPUB/PREREL/prhtml05/05139.html

Nikon (Nov 2005) Cameras, http://www.cpsc.gov/CPSCPUB/PREREL/prhtml06/06023.html

Kyocera Cell Phone (Nov 2004), http://www.cpsc.gov/CPSCPUB/PREREL/prhtml04/04068.html

Polaroid (Dec 2005) DVD players, http://www.cpsc.gov/CPSCPUB/PREREL/prhtml06/06060.html

Dell (multiple)(most recent-Dec 2005) Laptops, http://www.cpsc.gov/CPSCPUB/PREREL/prhtml06/06056.html

Minitec, portable DVD players, http://www.cpsc.gov/CPSCPUB/PREREL/prhtml05/05187.html



Page 4 of this document, talks about the multitude of safety measures that have been put in place on Li-Ion cells to prevent them from exploding, and for good reason:
http://www.cpsc.gov/LIBRARY/FOIA/meetings/mtg04/battery.pdf


Remember, I am not saying avoid Li-Ion cells, just be careful, they really can be dangerous, especially if mistreated during discharge/charge, and remember, there are a variety of protection mechanisms that I feel are really important.

 

[NewBie]

Quick question. I use an unprotected RCR2 li-ion in an Orb Raw with 3w luxeon emitter. I charge this cell in a small NanoCharger. It say 310ma on the cell.
Do I have to concern myself with anything that is written here?

Well, what is the maximum discharge current when the cell if fresh? What is the discharge rating for the cell you are using?

 

[HighLight]

Well, what is the maximum discharge current when the cell if fresh? What is the discharge rating for the cell you are using?

I think the discharge rate is around 1 amp when used in the orb Raw. Theres no electronics in the light or the cell. Its just direct drive so to speak. As for the discharge rating none was supplied with the cell.

 

[NewBie]

Quick question. I use an unprotected RCR2 li-ion in an Orb Raw with 3w luxeon emitter. I charge this cell in a small NanoCharger. It say 310ma on the cell.
Do I have to concern myself with anything that is written here?

I think the discharge rate is around 1 amp when used in the orb Raw. Theres no electronics in the light or the cell. Its just direct drive so to speak. As for the discharge rating none was supplied with the cell.

Well, since the cell says 310mA on it, if we take (1000mA=1A) 1000mA/310mA, thats well over a 3C discharge rate, which does sound pretty excessive. Though, the cell is so small, that if it goes off, hopefully it will only do localized damage. I certainly hope you do not carry it in a front pants pocket...

 

[greenLED]

I guess this is slightly OT, but why don't li-ion cells have raised "button-tops"?

 

[HighLight]

Well, since the cell says 310mA on it, if we take (1000mA=1A) 1000mA/310mA, thats well over a 3C discharge rate, which does sound pretty excessive. Though, the cell is so small, that if it goes off, hopefully it will only do localized damage. I certainly hope you do not carry it in a front pants pocket...

I won't carry it there from now on..

 

[lasercrazy]

I guess this is slightly OT, but why don't li-ion cells have raised "button-tops"?

I know what's up with that? It's so annoying trying to find something to raise the height to make contact.

 

[greenLED]

I was wondering... is it a safety issue?

 

[goldserve]

I have a question and excuse my laziness to check all the data sheets! Information overload!

If I were to design a circuit to indicate low voltage and a cutoff voltage, what should these be?

 

[carrot]

I'm curious to know how much of this applies to lithium primaries (such as CR123As) and alkaline primaries (in AA and AAA, specifically).

 

[SilverFox]

Hello Goldserve,

It depends on the current. The lower the current, the higher the cut off needs to be.

Tom

 

[SilverFox]

Hello Carrot,

With primaries, you don't have to worry about the recharge cycle. If you happen to damage the primary cell during discharge, you throw it out and replace it with a new cell.

In general, Lithium chemistry has a higher energy density than NiCd, NiMh, Alkaline, and Carbon Zinc chemistries. Higher energy density carries with it the possibility of higher risk.

Tom

 

[goldserve]

Hrm...that will throw a kink in things. I can't say cut-off at 3V no mater the current?

If I made the cut off at 2.7V but still let to user turn on the light and draw a minimal of 10ma, how bad is that? This would let the user know when he/she can't change the brightness anymore. I don't want to completely shut off the light because what if it was an emergency that the light was needed.

 

[SilverFox]

Hello Goldserve,

With a multi current light, you could set your low voltage cut off based on the maximum current draw. Once the light went out, you could then let it rest for a few minutes and get some additional run time at a lower current setting.

In emergency use when your primary light goes out, you simply employ your back up light, and reach for the spare batteries you are carrying for your primary light...

Tom

 

[Luna]

I guess this is slightly OT, but why don't li-ion cells have raised "button-tops"?

My guess is: they are meant be pack assembled only, IE industrial use