Prismatic Pouches vs Cans (18650, 26650)

[markz]

What are the advantages of Prismatic Pouches over cans?

The reason I ask is because if I put 12S 10Ah 3.7Vmax pouches (8.4mmx60mmx260mm) in that same space using 3.5Ah cans I double capacity, but perhaps discharge amps are lost and maybe thats a bad example. Would other suppliers of Prismatic pouches have more density.

I want density (more Ah) then anything else, in a smaller space.
18650 PF (2.9Ah) or 29E (2.9Ah) or even the 35E (3.5Ah)

 

[jonescg]

Ahh the age-old discussion about 18650s versus pouch cells...

Based on my reading of the numbers, 18650 cells (wound cells stuffed in a can) generally have higher energy density than pouch cells, but they have lower discharge rates.
The rolled up active layers may be much thinner so you can pack more special sauce in per litre of cell. When wound tightly around a mandrel, the resulting rigidity provides for a robust structure. Stick this inside a tube with constant radius, you won't get any major shape-changing take place, even if you try to induce some mild 'puffing'. The cylindrical cell's discharge capability is limited by the thin nickel strip connecting the centre of the 'jelly-roll' to the positive tab.

A pouch cell cannot be rolled and pressed as tight as a cylinder, so using a higher active material to current collector ratio is tough. The cells may easily deform and delaminate, increasing internal resistance and creating opportunities for self-discharge. However the current collectors can easily be made thicker and the terminations wider, so you can push more current through them. Generally the highest specific power of any cell format is a pouch cell.

Both cells are a challenge to actively cool, but theoretically a pouch cell has better surface area to volume ratio, making it better at shedding heat, all things being equal.

I've found some pouch cells offering 208 Wh/kg at 1C, but more like 186 Wh/kg if you hit them at 3C.

 

[Hillhater]

What are the advantages of Prismatic Pouches over cans?

The reason I ask is because if I put 12S 10Ah 3.7Vmax pouches (8.4mmx60mmx260mm) in that same space using 3.5Ah cans I double capacity, but perhaps discharge amps are lost and maybe thats a bad example. Would other suppliers of Prismatic pouches have more density.
I want density (more Ah) then anything else, in a smaller space.
18650 PF (2.9Ah) or 29E (2.9Ah) or even the 35E (3.5Ah)

Doubtful you can beat the 18650s for Wh/litre or Wh/kg
...but you can get a lot better energy density than those pouches you are looking at !
Try the Turnigy Multistar packs....they are much more compact.
They can support 2-3 times the current discharge of a 35E
The other advantage of Multistars or similar packs, is that they are "plug and play" ...simple to couple a pair of bricks into a 12s pack , with no welding, soldering, glueing, wireing, tapeing etcetc.

 

[markz]

Those pouches from BMSB were just ones I found easy enough, wanted to get size, v and ah.

I want the most Ah per volume of space. Them cans arent efficient that way, flat pouches are more efficient.

 

[Hillhater]

pouches may fill more % of the space, but the cans will probably still win on a purely Ah/pack volume comparison...
....even with the air gaps !
This all depends on which cells you use, and what other factors you want to consider.

 

[amberwolf]

I want the most Ah per volume of space.

Keep in mind that sometimes you get the most Ah from the lowest-capability (lowest-c-rate)...but then to get the current-delivery you need you may end up having to build a bigger (more Ah/size) pack than you would have with other cells that had lower Ah.

So it's a balance....

 

[jonescg]

Keep in mind that sometimes you get the most Ah from the lowest-capability (lowest-c-rate)...but then to get the current-delivery you need you may end up having to build a bigger (more Ah/size) pack than you would have with other cells that had lower Ah.

So it's a balance....

Yep -

https://endless-sphere.com/forums/download/file.php?id=216508

This is a 7000 mAh cell rated at 5 C peak.

At 1 C I calculate 208 Wh/kg
At 2C I calculate 185 Wh/kg :?
At 3.5 C I calculate 177 Wh/kg :x

So a 10 C rated cell will deliver 177 Wh/kg at 3.5C and still do reasonably well at higher rates still. So C-rate matters!

 

[marcexec]

Don't forget you have to compress the pouch cells - that will add bulk (assuming mounting being equal).