Cells for high drain battery

[Chalo]

prismatic is troublesome to use as you need massive steel supports to compress them. that often negates any advantage they might have.
i'll switch to prismatic/pouches once they start making professional power tools with them.

My 1.2 kWh pack made from prismatic cells has two 1/4" aluminum plates held together by 4 sticks of 1/4" all thread. Compared to 500+ strips and welds, that was a cakewalk. The cells are rated for 500A peak, but I discharge at 35A peak, so any kind of compression is probably only a formality. But it gives the pack some structural integrity, so that's worthwhile.

My cordless drill has 1/10 the amp-hours of my bike's pack. So it makes sense that the cells are about 10% the capacity of the ones in my bike. Would it make sense for the pack in my cordless drill to be made of highly parallel groups of 250mAh cells? No, it would not. The same way it doesn't make sense to make similarly parallel bike packs from lipstick cells.

 

[flippy]

That math does not make sense. A 1.2kWh pack made with 18650 can be made with less then 100 cells.
And quarter inch alu is also heavy as is the rods and bolts and it limits the shape of the battery.

And a tesla has 15000 welds and their packs basically never breaks.

 

[Chalo]

That math does not make sense. A 1.2kWh pack made with 18650 can be made with less then 100 cells.

Ok then, 100 strips and 200 welds. I'll take 2 plates and 4 studs every time.

7P lipstick cells won't push 300 amps, but my pack will anytime I want.

 

[john61ct]

The greater ease of monitoring and balancing a smaller cell count is a plus.

As is easy breaking down and reassembly of the pack for swapping out of individual cells.

The greater bulk of LFP (lower energy density per weight/volume) and blocky shape is a downside for some use cases though for sure, e.g. small & nimble MTB, as opposed to a big heavy cargo bike.

 

[Chalo]

The greater bulk of LFP (lower energy density per weight/volume) and blocky shape is a downside for some use cases though for sure, e.g. small & nimble MTB, as opposed to a big heavy cargo bike.

That's true. Prismatic cells for automotive applications seem to be compromised for high current rather than maximum Wh/kg. So even those with NMC or NCA chemistry tend to be larger and heavier per watt-hour than high performance 18650.

It's all so much better than what was available even a few years ago, though, that I don't mind carrying a slightly larger battery than the most energy-dense version possible.

 

[flippy]

"slighty" is a understatment, its litteraly double the cell weight and then you need to add the massive metal anti-bulge structure.

 

[john61ct]

Any links to large prismatics sold as new bare cells that are non-LFP LI?

 

[Chalo]

"slighty" is a understatment, its litteraly double the cell weight and then you need to add the massive metal anti-bulge structure.

"Massive". My compression frame for a 1.2 kWh prismatic pack weighs less than the case and rail for my 650 Wh Shark pack. And partly because of the edge and corner protection of the frame, it doesn't need a case and rail-- only a zipper bag with some light padding.

Anyway, the best lipstick cells have better energy density per mass, but automotive prismatics have superior power density per mass (and better geometric density). So saying one is categorically lighter than the other means ignoring the way in which it isn't.

 

[Chalo]

Any links to large prismatics sold as new bare cells that are non-LFP LI?

I've never been interested in paying for new large format cells, given that it's so very cost-effective to salvage cells with years of good life left in them.

These are the ones that have me most interested lately, though I haven't gotten any yet:
https://www.ebay.com/itm/42-SPIM08HP-3-7V-8AH-LITHIUM-POLYMER-BATTERIES-25C-200A-SUPER-CELLS-24V-36V-48V/202508210597

These are the prismatic cells I've built the most packs with, and which are my favorites to work with.

 

[john61ct]

Yah pouches do not interest me as much as prismatics, iow already encased, bolt terminals

 

[john61ct]

Hey! I found some cylindrical lithium ion cells on Alibaba for less than $.04 each!
https://m.alibaba.com/product/60759912679/SNeng-3-7V-Rechargeable-Li-ion.html

6500 of those should make a nice 48V 20Ah bike pack that can be shaped to fit almost any frame. Cheap, too-- less than $250 per kWh and each in its own metal case. What a bargain!

https://www.diyelectriccar.com/forums/showthread.php?p=1036403