Seek advice on low-impedance Li-ion battery.

[evalon]

Hi All,

I have a question that I hope I can get help with here in this forum ... As it is I'm looking for a very low-impedance Li-ion (or other chemistry with a 50% charged voltage of appr. 4 - 4.1 VDC) battery in the size 26650. I've been considering e.g. the Panasonic CGR 26650B (<= 14 mohms internal impedance), however, can't find a vendor of these for low Nos. Also, I'd be interested in finding a cell with an even lower internal impedance, if possible.

Anyone here knows of either a vendor source of these panasonic cells in low Nos (and - just if possible - close to Denmark) - or an even lower impedance cell?

Thanks for any help in this :wink:

Jesper

 

[redilast]

Why are you after 26650?

Almost all the R&D is going into 18650 and they have much higher energy density. The lowest impedance 26650 I know of is A123 systems LiFePo4 26650 which is ~8 mili ohms @ 1Khz AC. Other than that, brand name 26650's are difficult to source.

There are other brands like MNKE IMR 26650's which they might have some models with ~15 mili ohms internal resistance but I can't really recommend them as they seem to suffer from the internal resistance just increasing significantly when left in an idle state.

Sony VTC4's are around 13 mili ohms, VTC5 around 14 and Samsung 25R / LG HE4 around 15 mili ohms. But these are all 18650.

 

[evalon]

Hi redilast,

Thanks for your feedback. Actually, my reason for being interested in 26650 batteries is their potentially lower internal impedance. I've been searching some for 18650 cells with low internal impedance, however, have not really found any - most of them had impedances in the 40 - 60 mohm range which is too high for my purposes.

But your suggestions (Sony & Samsung) in 18650 sizes are fine with me - and actually what I was looking for. I have some A123systems cells already but their voltage level is a bit too low in this context.

So thanks - I think I have had help for what I was looking for ...

Cheers :wink:

Jesper

 

[Hillhater]

Hi All,
... As it is I'm looking for a very low-impedance Li-ion (or other chemistry with a 50% charged voltage of appr. 4 - 4.1 VDC)

Jesper

50% charged voltage of 4+ volts ??......that will be a problem !
Most Li cells operate between 2.5 - 4.2 volts, with a 50% capacity at 3.9v or lower.

 

[Peter.bp]

At 50% SOC usually you can expect voltage between 3.6 and 3.7V, sometimes even lower (at 1C discharging current)...

 

[evalon]

Hi .. Hillhater & Peter.bp,

Sorry, my mistake in wording my question correctly. What I need is a battery which at a reasonable charge (50 - 100%) that has a voltage around 4 - 4.1 VDC so a Li-ion battery may well be what I am looking for. And as I wrote I've already gotten a fine help with the batteries mentioned so I can progress from here. But thanks for observing that in case I had worded my question correctly there would have been an issue with the voltage :wink:

Cheers,

Jesper

 

[Hillhater]

If that 4+ volts is critical for your use, be aware that Li ion cells do not hold in that range for very long once in use at any significant discharge rate.
Check out some of the discharge curves on here or supplier data sheets for details.

 

[jonescg]

I can see your reasoning for the 26650s - A123 had some very high discharge 26650s with very low internal resistance. However these run at 3.2 V nominally. Ideal for making a 12 volt equivalent battery with 4 in series.
All the 18650 cells I've seen have higher internal resistance, and their cycle life isn't that impressive.

 

[liveforphysics]

You can get a lower resistance pack made from Sony VTC5's than A123 26650 M1 cells for a given pack volume/mass. That same pack volume and mass also holds about 2x more energy.

If you don't have a super high C-rate need, LG HG2 cells are quite nice performers for a 3Ah 18650, they can really handle 20A continuous.

If you need the lowest impedance (drag racing etc), sadly it's found inside the hobby pouches.