Error in an ECF Library Rechargeable Batteries article

[jmanning]

I wanted to PM the author first on this, but I am not able to.

The article in the ECF Library article "Rechargeable batteries" has a very large error in the information on LiFePO4 batteries, stating that the "Discharge rate is 10C+". From my research, AW LiFePO4 have a max discharge of 700mA, Tenergy at <550mA, and Powerizer at 675mA. This puts their C rating at 1.5C or less. In almost every case these batteries are being over-stressed when used in a PV. For this reason, I believe placing these batteries above name brand protected lithium-ion batteries in suitability for vaping is questionable and should be re-evaluated.

 

[rolygate]

The wording should be "...the discharge rate can be 10C+...", not "is". Thanks for pointing this out. The whole point about Li-FePo4's is that they have a very high discharge rate, often higher than AW's Li-Mn's for example, and have the safe chemistry needed for use in mods.

The discharge rate is commonly 5C to 8C for a good LiFePo4 and in some cases can be as much as 10C, which is why a Li-FePo4 cell has the highest discharge current I've seen for these small cells - 10C / 70 amps if shorted out, I think it is an AW Li-FePo4 'C'-size cell like a 26650 but not too sure (from memory).

See these links for Li-FePo4's with a 10C rating:
http://www.batteriesinaflash.com/as...-cylindrical-rechargeable-battery-3-2v-800mah
http://www.batteriesinaflash.com/as...cylindrical-rechargeable-battery-3-2v-2000mah

Because Li-FePo4 cells are commonly 5C to 8C discharge rating, and this high discharge capacity is what they are famous for, I don't really know what to make of Tenergy's "<550mA". Less than 550mA is the rating of a standard Li-ion cell and Li-FePo4's have many times their discharge rating (or we wouldn't be discussing them).

Maybe it's a misprint or something. Or maybe they have come up with a new, cheap format with incredibly poor performance. Who knows. I'd ask the factory about this before putting any credence on adverts showing Li-FePo4 cells with less output capability than a Li-ion.

 

[jmanning]

The ones that concern me are the smaller RCR123a/16340 LiFePO4s that so many people seem to be using in a stacked configuration in order to get 6v. Stacking batteries has its own set of issues that must be paid attention to, and throwing in over-stressing these little batteries to the mix is an accident waiting to happen.

 

[rolygate]

Yes. But there is something going on here. Normally you'd figure the smallest possible C rating for a Li-FePo4 would be 4 or 5C, and some go to 10C. After all you can get 70 amps out of one Li-FePo4 model in a dead short, the highest amount for any small cell.

Either the quoted discharge for these Tenergy cells is a misprint or they aren't true Li-FePo4 cells. They can't be, at that rating.

 

[Papa Lazarou]

Just an FYI, Tenergy actually sell a range of LiFePO4 "10C" cells with a max rated output of 10C (10 times the capacity rating). See the yellow ones at this link - http://www.tenergybattery.com/index...ategory_id=21&option=com_virtuemart&Itemid=27 The 18650's are claimed to output an incredible 40A in short bursts.

I've not put it to the test but apart from the higher discharge ratings of LiFePO4 cells (compared to LiIon) the main advantage is that they are not supposed to vent with a flame. Likewise for the LiMn batteries.

 

[rolygate]

So, what we are seeing here is a new range of 'weak' Li-FePo4 cells that aren't true Li-FePo4 and are rated at even less than a poor-quality Li-ion?

Interesting. If this is the case, we'll have to make a radical change to our advice about Li-FePo4's, if they are making a two-tier system now.

 

[dspin]

Great thread guys, look forward to more info. We all need this.

 

[Papa Lazarou]

It does sound like it is the case that not all of them are alike. An interesting thread on CPF Forums - Tenergy Lifepo4 3 volt questions The last comment (14) is particularly interesting.

I think it's the yellow "10C" batteries which are recent additions to Tenergy's range. The Tenergy batteries with the low discharge rating have been around for a couple of years at least. I have a few sets. All I can say is they do get considerably weaker after a period of time, which seems consistent with what was being said on CPF.

 

[jmanning]

Has anyone seen 16340/RCR123a sized LiFePO4 batts, the kind you would stack for 6v, that do have higher C rating? All I have found with the higher rating are larger cells, 18500, 18650, and larger.