LiFePO4 in 18650 format?

[Honk]

Don't get me wrong but Samsung INR18650-29E is based on NCA chemistry like many others cells in 18650 Samsung production line. For example 30Q, 25R, 48G and others...

Well, here's another "don't get me wrong" :wink:
29E is not NCA and that's an old misconception based on scarce data in the early days of the cell being released for sale.
An NCA cell contains aluminium of importance (that's what the capital A stands for) but there is no aluminum in the 29E.
The 35E on the other hand is really NCA.

Here is the evidence of Samsung 29E really being NCM -> LiNiaCobMn1-a-bO2
Detailed datasheet on the chemistry of 29E: http://cdn14.21dianyuan.com/download.php?id=238880

I have read the same info at another technical site, where the 29E was discussed in detail and proven as NCM, but I can't find it right now.
Please feel free to look around yourself.

The good side of 29E is that all cycle and life tests show it being among the best cells out there, beating the crap out 35E.
I prefer longevity ahead of short lived top notch capacity.
The 29E is more than adequate when designing large packs, in my case 4pcs of 12S8P = 45V 22.8Ah that operates in parallel as a 4kW pack.
Well, actually only 3.6kW as I only charge to 90% full at 4.1V.

 

[Pajda]

Thanks for this document this seems to be more credible than "Samsung 29E cell Introduction" document where they are talking about NCA chemistry. http://www.goeke-intermedia.de/tradepro/shop/artikel/allgemein/Datenblatt_INR18650-29E.pdf

I can confirm by my own tests that 29E is the cell with one of the highest cycle life in Samsung production line of small cylindrical cells. But almost all competitors from other manufacturers with similar energy density have the cycle life significantly better. In short I am disappointed with the cycle life of the whole Samsung 18650 and 21700 production line.

 

[Honk]

Can you recommend another cell brand and type beating the 29E? (with test data)
It's always good to keep up the news on great cells.
Pehaps they can be found at equally competetive price as 29E if lucky.

 

[flippy]

Can you recommend another cell brand and type beating the 29E? (with test data)
It's always good to keep up the news on great cells.
Pehaps they can be found at equally competetive price as 29E if lucky.

if they exist i have not found them. the panny PF's are measureably losing to the 29E's after a few hundred cycles.

 

[Honk]

Looks like I bet on the right horse when I selected 29E for my project just because they where the most affordable high density cells.

 

[Pajda]

Looks like I bet on the right horse when I selected 29E for my project just because they where the most affordable high density cells.

Yes, the 29E seems to be the only one cell in the whole Samsung 18650 high energy density production line with good cycle life. Samsung cells with lower density like 25R or 26J are also good, but everything above 2900 mAh has very poor cycle life. In fact that should be the meaning of my previous post. Competitor cells shows very good cycle life (even better than 29E) for cells up to 3500mAh. But the price per kWh is significantly higher. If I compare cycle life of 29E with PF under my standard 0.5C-1C 100% DoD test, the result is that there is no significant difference. PF starts losing its capacity more rapidly but after ca 500 cycles the capacity drop stabilises. The 29E shows from the begining slower and mostly linear capacity drop. After ca 700 cycles their capacity loss is equalised and the 29E starts at this time losing a little against PF. Unfortunatelly I did not already test the LG MG1 competitor. Most of LG cells showed excellent cycle life so it i suppose that there will be no exception in this case.

 

[Honk]

Do you have any site or forum page with compiled test data on various cells?

 

[flippy]

here is a 29E after 1200+ cycles:

90% of cycles are 4.05V>3.5V.
draw peaks are between 1A continous and 8A peak.

so about 200mAh loss after 1000 cycles is nothing less then perfect. this is also a 1A drain cycle and the official spec is based on 0.2C so there is that...

 

[Pajda]

yes, your result is consistent with my measurement for 29E. Under 0.5-1C cycle test:

100% DoD test (4.2-2.5V): 70% of nominal capacity after 1000 cycles
50% DoD test (4.2-3.55V): 91% of nominal capacity after 1000 cycles

but it should be noted that under such low DoD (35% ?) almost all cells on the market will perform well.

 

[flippy]

Not all cells, the GA's i have on the torture tester are already losing capacity after 300 cycles.

 

[Honk]

What do you estimate the cycle life being at approx 50% DoD and gentle slow charge at 0.2C to 4.1V.

 

[Pajda]

Not all cells, the GA's i have on the torture tester are already losing capacity after 300 cycles.

under what settings? My GA samples works fine under 0.5C-1C at 50% DoD(4.2V-3.55V) with only small (up to 5%) capacity loss after 500 cycles. This behaviour is typical for almost all cells on the market. Yes, under a high DoD GA losses capacity from the beginning very quickly, but after reaching about 500 cycles, the capacity drop is slowing down.

 

[flippy]

i pull them down to 3V on the tester on a 1 and 2A load.

 

[john61ct]

LFP is the bomb for longevity, lots of 2000 cycle banks out there (non propulsion) getting on to ten years with Zero capacity loss

but little cylindricals are rare other than A123,

prismatics much more common and useful for storage banks.

I consider 20Ah to be tiny, the 180+Ah cells great for most use cases. Seen some Winston over 1000Ah, big mofo's.

Cycle between 2.99V and 3.45V, gentle sub-C rates and can get decades, 10,000+ cycles.

I think calendar aging will end up being the limiting factor.

 

[amberwolf]

but little cylindricals are rare other than A123,

Not really. There've been plenty of small (ebike sized) packs from manufacturers, built with 18650 LiFePO4 cells. If they're still around, CammyCC, Vpower, and another one I forget the name of are made this way. They're usually pretty crappy cells, and even crappier pack construction, but they're out there.



Then I guess there's Headway, which isn't 18650, nor really "little", but common enough.

 

[flippy]

lifepo4's are in this day just dumb. for the same space and usually less cost you can build a lipo battery that will outpreform lifepo4 in every regard, even lifespan if you charge it correctly. (aka: up to 4.05v)

lifepo4 had their place the past 15 years but the cost and performance of lipo has passed it right into the bin as a choice for basically any application.

 

[john61ct]

I'd be very interested in hearing from anyone using a daily cycled 300+Ah storage bank, for over a decade without capacity loss.

For me, installed and charged/used unattended inside a small mobile living space, perhaps with spouse and kids,

means LFP or lead are the only choices.

 

[flippy]

i happen to just have finished my calculations on a samsung 29E with 500 cycles on my destruct-a-cell.

test specs:

4.05V to 3V with a 1.3A charge and 2.75A discharge current

new: 9.534Wh
after 500 cycles:9.487Wh
please note, this test took months of non stop constant cycling, this is years of daily full discharges at their rated currents.

this is LESS then 0.5% loss in capacity.
so no, you are NOT going to wear out these cells anytime soon if you stick between the lines.

 

[Honk]

Wow, great results.
29E will make it into the history book of famous immortal cells at the best price range possible.
I must invest in plenty of these great little suckers and store them cold for the years to come.

 

[docware]

this is LESS then 0.5% loss in capacity.
so no, you are NOT going to wear out these cells anytime soon if you stick between the lines.
[/quote]

Can you please specify your test equipment and conditions (temperature) ?

 

[flippy]

Can you please specify your test equipment and conditions (temperature) ?

i have dedicated battery testers from several brands. the unit that does the current batch of 29E's is a 8 channel tester from EBX capable of pushing and pulling 10A per cel.
temperatures were pretty equal between 15~20c depending on the other loads in the room.
temperature is not a measureable factor in these tests as the test duration is meastured in months. i do see a slight change in capacity when the temperature changes a bit but over the course of a dozen weeks the curve gets pretty flat.

my test with these cells (the 6 and 7 series) is still running for the lower stress and high stress runs but they are showing very good numbers so far considering.

 

[docware]

the unit that does the current batch of 29E's is a 8 channel tester from EBX capable of pushing and pulling 10A per cel.
temperatures were pretty equal between 15~20c depending on the other loads in the room.
temperature is not a measureable factor in these tests as the test duration is meastured in months.

Well, ZKETECH EBX tester. How often do you calibrate EBX channels ? What equiment do you use for calibration ? How do you measure temperature, do you have temperature logger in the room ?

 

[flippy]

Well, ZKETECH EBX tester. How often do you calibrate EBX channels ? What equiment do you use for calibration ? How do you measure temperature, do you have temperature logger in the room ?

a BM867s was used for callibration. wich is done between every test run. or do you prefer a banged up fluke 87?
i use a old style lab grade flask thermometer for room temperature for funsies. not very relevant as the room is kept between 15 and 20c by the heater/aircon at all times.
not good enough for you?

 

[docware]

I own ZKETECH EBC – X510, believe me I know what I am speaking about. If you measured 0,5 % difference, then accuracy of the equipment has to be at least 0.1% or better. Frankly, achieve 0.1% accuracy at capacity measurement is not easy. You need to have voltage and curent calibrated to values better than 0,1 %. And check the current during whole measurement. From your calibration description is not clear if you calibrate current also.

Temperature difference 5 °C during capacity measurement can affect result cca 1 – 2 %. Moreover, your temperature measurement is not very accurate and somewhat vague, similarly as calibration description.

Did you measure capacity before start and after 500 cycles at EBX tester or at different equipment ?
What cell fixture do you use ?

I also did some cycle testing. Frankly, 0,5 % capacity loss after such 500 cycles is shortly nonsense. Can you show capacity curve of the test ?

 

[Punx0r]

Assuming I'm looking at the correct datasheet, the manufacturer claims 70% capacity after 500 cycles: https://eu.nkon.nl/sk/k/29E.pdf