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Old 10-11-2012, 06:47 AM   #1 (permalink)
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Lithium-ion Battery Question

Electric vehicles often have hundreds, if not thousands of Lithium-ion cells that make up their battery. The size seems to be CR123 or similar. Why aren't lithium-ion cells made in larger sizes? For example, a lead acid battery can be found in very large sizes, but you never see a lithium-ion battery with those dimensions.

Could a vehicle battery pack be constructed with the use of fewer, but larger cells?

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Old 10-11-2012, 06:59 AM   #2 (permalink)
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Are you just baiting?

Lots of EV folks use these sort of prismatic cells, e.g. 3.2 volts, 180 AHr capacity

http://www.electricmotorsport.com/st...ll_variety.jpg
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Old 10-11-2012, 10:28 AM   #3 (permalink)
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Most EV's don't use 1,000's, except for Tesla, because they are stuck in their old ways of doing things, they are using spiral wound cells that look kind of like flashlight batteries, hybrid battery packs are currently the same way.
Vehicles like the Nissan Leaf, Chevy Volt, Mitsubishi i, Ford Focus-EV and I think even the Plug-in Prius all use pouch or prismatic cells, lithium cells that are also called Large Format, I have 8 such cells sitting on my desk right now, 100amp hour 3.2v cells the size of a chunk of 2x6 9" long/tall.

The advantage of course with small cells is that you can make your pack in pretty much any shape you want, they are also already mass produced for things like tools and lap tops, the draw back, and it's a big draw back, is that each battery has a connection and that is a point that it can fail, so you have 10,000 flashlight batteries and you end up with 10,000 connections and in theory you should have a battery management system that can connect to all 10,000 batteries so you have 10,000 little wires running to a BMS, then you run in to an issue of how do you tap power off that battery pack and have it stay even? wire, even short runs, has resistance, so the battery closest to the output cable will have the highest draw!
My electric car is a low voltage car, running at 48v, if I end up with these batteries in it instead of my motorcycle... it will have 16 connections between batteries, 16 BMS connections and my lithium batteries are wired up in sets of 4 with solid bars between cells, so my interconnect cables with their crimp on connectors and so on are reduced down to 3 and 2 power cables coming off each side of the pack.
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Old 10-11-2012, 06:04 PM   #4 (permalink)
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I use 48 A123, they are roughly C-cell sized.
Next time around I plan on using paper backed book sized rectangular cells.

Buying the raw cells is a lot cheaper then getting a premade battery.
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Old 10-12-2012, 01:10 AM   #5 (permalink)
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I had no idea Li-Ion cells came in anything other than small cylinders. I've seen Li-Po batteries in various sizes in rectangular shapes, but I'm not sure how the chemistry differs from Li-Ion.

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Originally Posted by oil pan 4 View Post
I use 48 A123, they are roughly C-cell sized.
Next time around I plan on using paper backed book sized rectangular cells.

Buying the raw cells is a lot cheaper then getting a premade battery.
Why would you go with with rectangular cells if the A123 are cheaper?

I would think making larger cells would be more cost effective for companies like Tesla. Much less complexity for a BMS, less cost in packaging, and most importantly, higher energy density since less packaging material is required, and less space is wasted due to fitting cylindrical objects into a rectangular area.
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Old 10-12-2012, 08:17 PM   #6 (permalink)
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For CCA/$ and AHr/$ I believe the rectangular cells should be cheaper.
And it will be a lot easier to wire up 8 (maybe 12) cells versus 48 cells.

The space aloted for the batteries is two 30 caliber ammo cans.
Have you seen the pic?
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Old 10-12-2012, 11:37 PM   #7 (permalink)
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There are lots of prismatic cells - the ones I was planning on for CarBEN EV5 are 5.5" x 10.5" x 0.375". They look like flat plates. The 48 cells in a Nissan Leaf are roughly 1" thick by a foot by 8 inches. The cells in a Volt are also prismatic.

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