LiFePO4 vs IMR - safety

Hey everyone,

I'm looking to purchase new 123a sized AW rechargeable batteries. So far I'm leaning towards LiFePO4's, but the IMRs are also advertised as being 'safe', i.e. no going . The LiFePO4's are 3.2V while the IMRs are 3.7. Which one is truely more explosion proof when being handled by a complete battery beginner?

thanks

Just placed an order for AW 4x 3.2v LiFePO4 and a charger. These batteries should work without a hitch in any light that is capable of handling 3.7v Li-ions, right? Could someone confirm this please.

did you ever find out which is safer (LiFePo4 vs IMR?)?

From what I've read LiFePO4 should be The Most intrinsically safe chemistry, this battery chemistry doesn't have the energy density that Lithium Ion batteries do, but still more than NiMh.
I don't have any LiFePO4 batteries, but I've been curious about them and been reading up on them.
I also inquired about running a light with LiFePO4 which had been designed for CR123 batteries. The manufacturer replied that the light would not be harmed but that performance might suffer.

LiFePO4 is a lithium ion battery.
IFR is safer than IMR, for about the same runtime.

Depending on the light (i.e. Zebralight), NiMH has some important advantages. One of those advantages is the light not cutting out leaving you in the dark. If you don't run on high output, NiMH has better runtime.

eh4 said:

this battery chemistry doesn't have the energy density that Lithium Ion batteries do

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IFR (LiFePO4) is safer than IMR, and nominal voltage is also lower. This means that it's a more direct replacement for 3.0V primaries, as some lights have compatibility issues with the extra voltage from 3.7V Li-Ions.

snakyjake said:

Depending on the light (i.e. Zebralight), NiMH has some important advantages. One of those advantages is the light not cutting out leaving you in the dark. If you don't run on high output, NiMH has better runtime.

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Same goes for LiFePO4, there's no protection circuitry needed, so if battery charge gets low, you can operate on a lower mode.

aimxplode said:

Just placed an order for AW 4x 3.2v LiFePO4 and a charger. These batteries should work without a hitch in any light that is capable of handling 3.7v Li-ions, right? Could someone confirm this please.

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Emphasis mine.

The answer to that question is no, if by "any" you really mean "every".

Or we could say "it depends". Always check with your light supplier what its requirements are.

A LiFEPO4 fresh off the charger, not under load, will probably show a voltage between 3.4 and 3.6V; under load you'll see it drop towards the 3.2V nominal voltage sooner than later.

If a light is designed around standard li-ion cells, 3.2V would be seen after much of the capacity has been depleted from a cell. There might not be much runtime available in such a light below 3.2V, which would be a problem for such a light if feeding the light LiFEPO4 cells. Depending on the driver used by a light, the under-load voltage of a LiFEPO4 cell might bring the light out of regulation and into direct drive and declining output, if the light is designed in that manner.

Lights primarily designed for 1xCR123 or 2xCR123 ought to do well enough with LiFEPO4 as long as they can take the slight over-voltage 1x or 2xLiFEPO4 present when fully charged.

Again... it depends. Check with your light maker before buying cells. Many will probably work fine but don't guess or risk

eh4 said:

From what I've read LiFePO4 should be The Most intrinsically safe chemistry, this battery chemistry doesn't have the energy density that Lithium Ion batteries do, but still more than NiMh.
I don't have any LiFePO4 batteries, but I've been curious about them and been reading up on them.
I also inquired about running a light with LiFePO4 which had been designed for CR123 batteries. The manufacturer replied that the light would not be harmed but that performance might suffer.

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The driver for Li-ion safety is decomposition temperature that releases oxygen. All of the Li-ion chemistries have plenty of energy density to be dangerous if they light off. The vapors aren't exactly healthful either. For LiFePO4, that temp is over 600C. LiMn2O4 is stable up to about 180C. LiCoO2 has shown thermal runaway at about 155C. However, LiCoO2 safety can be a tricky thing to quantify. It can start to react with its electrolyte at even 130C.

The Li-ion safety issue can be characterized as the cathode material "burning" the electrolyte. For LiCoO2, the cobalt is in a very unstable oxidation state and readily liberates oxygen, and then reacting with the organic electrolyte. Based on this, some researchers have proposed using oxygen chemical potential as a metric for cathode safety. LiCoO2 oxygen chemical potential is about +0.5eV and is thus "unsafe". LiMn2O4 is about -0.3eV and is "safer". LiFePO4 is about -1.6eV and is "safe".

Robin24k said:

there's no protection circuitry needed, so if battery charge gets low, you can operate on a lower mode.

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That's not what I saw from the runtime test. As you can see from the test, when not operating on the highest mode, NiMH is better.

Jake

What I meant was that if the light has cut-off due to insufficient voltage, you can wait for the battery to recover and then use it again on the low mode.

Capacity-wise, yes, NiMH edges out LiFePO4 for the AA size, but the LED is probably driven harder when using LiFePO4, so it's not an equal comparison. Furthermore, boost circuitry is more efficient with battery voltage closer to output voltage, so even for constant power drivers, constant power to the LED does not necessarily mean constant power from any battery.

I'm not sure what you're seeing from the runtime test, but for single cell AA lights, LiFePO4 will generally give you higher output for less runtime, and NiMH will give you lower output for more runtime. This applies to all modes, not just high.

I am still trying to make me a knowledge on lithium primary safety then I heard that rechargeable li-ion batteries with safe chemistry maybe even safer.

I see IMR should be safer in multi-cell applications but I always read to avoid unprotected batteries in series missing the voltage/short protection.
Most accidents I read here actually involved short circuit or bad voltage matching batteries in series.
How do they differ from li-ion when fail? Aren't safe chemistry batteries affected by short circuit or unmatched series?

I also see they still have vent holes at top like li-ions, if not venting with flames could still do same gas as li-ion?
In waterproof light venting gas would cause an explosion, doesn' it make standard protected li-ion safer in sealaed flashlights?
In e-cigarette forum I think I read a couple of explosion both involving IMR and LifePo4.

Making IMR/LifePo4 with same protection features of your li-ion won't be the best thing? I would be glad to spend more for a protected safe chemistry li-ion.

dantes said:

Making IMR/LifePo4 with same protection features of your li-ion won't be the best thing? I would be glad to spend more for a protected safe chemistry li-ion.

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One of the reasons why LiFePO4 (and perhaps some IMR) doesn't typically have protection is that these cells are typically designed around high current. Whereas a typical ICR 18650 often can't even kick out 10A, a LiFePO4 (IFR) can do 30A (or more). A protection circuit able to handle this kind of current would probably be too big for the battery and prohibitively expensive. In other words, a protected LiFePO4 18650 (or any size, for that matter) just couldn't do the very thing that is the strength of LiFePO4 chemistry.

StorminMatt said:

One of the reasons why LiFePO4 (and perhaps some IMR) doesn't typically have protection is that these cells are typically designed around high current. Whereas a typical ICR 18650 often can't even kick out 10A, a LiFePO4 (IFR) can do 30A (or more). A protection circuit able to handle this kind of current would probably be too big for the battery and prohibitively expensive. In other words, a protected LiFePO4 18650 (or any size, for that matter) just couldn't do the very thing that is the strength of LiFePO4 chemistry.

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With LiFeP04 you don't need the protection circuit as the functions the protection circuit provides are pretty much unneeded. No point adding cost and complexity when there is no value. Not all LiFeP04 can do really high currents either, they need to be designed for that.

Semiman

Is it ok to run down a LiFeP04 cell into low voltage discharge ? 2 volts ?

I bought a few AW IMR 18650 cells a while back and was going to run them in all my multi cell lights for safety. Then I realized that I can accidentally run them down into a battery damaging low voltage state ( did it ) because there is no protection circuit on the battery or a low voltage cut off in multi battery lights. I tried to be careful but 1600mah doesn't last long.
Now I just run my IMR cells in single cell application as backup. I find the end of the 1600 mah rating too fast compared to my lithium ion cells.

Lou Minescence said:

Is it ok to run down a LiFeP04 cell into low voltage discharge ? 2 volts ?

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I accidentally left a red LED powered by LiFePO4 cells switched on overnight last night. This morning, the voltage was well under 2 (much closer to 1) volts. The cells are 3-4 years old, and I thought they were probably toast. One of them took a little while on the charger before it started accepting a charge, even after resting for half an hour or so, but they both charged to their typical 3.4 volts.

Lou Minescence said:

Is it ok to run down a LiFeP04 cell into low voltage discharge?

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It will reduce the cell's life, but not increase safety risk.

dantes said:

I would be glad to spend more for a protected safe chemistry li-ion.

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LiCo cells need protection circuits because the chemistry is volatile and unsafe. LiFe doesn't need a protection circuit because the chemistry is stable and safe.