Why don't 26650s have more capacity?

rickypanecatyl

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So I made this silly chart comparing battery volume sizes and their "potential capacity" if compared with a 3,500 mA 18650. So for example, a battery that truly has the dimensions of 21mm diameter and 70mm length has 147% more volume than 18mm diameter x 60mm length battery. And a 147% of 3,500 mA = 5,145 mA which isn't far off the capacity of a good 21700.

Now I realize there are lots of other factors but I've never seen a 26650 with more than 5,000 mA capacity and just am curious why that is so short of the 7,315mA on my chart?
Any ideas? Possibly little demand so not much pushing of the envelope in that category?

Battery volumes
SIZE
MM3​
% 18650
potential mA
18650
16,532mm3
100%
3,500mA
21700
24,232mm3
147%
5,145mA
26650
34,493mm3
209%
7,315mA
16340
6,833mm3
41%
1,435mA
14500
7,693mm3
47%
1,645mA
24900
40,694mm3
246%
8,610mA


I put a hypothetical 24900 battery at the bottom as I've got large hands and that would probably be my "dream size" for an EDC size light. An SBT 90.2 in a light with a 30mm diameter body and a 40mm diameter head... wouldn't seem much bigger in my pocket than a 18650 light with a 25mm body and 40mm head! :grin2:
 

vicv

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I think because 18650 and 21700 are industry sizes and are mass produced for tools and cars. Nothing really uses 26650s so they're not made with the new cell materials.
 

john61ct

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Lots of 26650 are LFP rather than li-ion

inherently lower energy density

but much safer and last tem times longer

A123 way better than any others
 

idleprocess

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Outside of flashlights, vape boxes seem to be the main market for the 26650 thus there's little financial incentive to develop the 26650 to its maximum potential - more or less how vicv put it.

Heck, the 4680 that Tesla is developing should hit something like 25Ah (or 25,000mAH if we're going to abuse engineering notation) if their Ah/unit volume remain consistent with 18650 and 21700.
 

john61ct

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26650s are commonly used for energy storage powerpaks, solar, mobile House banks, etc

A123s will last for many decades, many thousands of cycles and are much safer than the higher voltage li-ion chemistries.

Marginal lower energy density is NBD for most use cases, still half the weight of the lead banks they are replacing, 100Ah even at 24V is still very portable.
 

vicv

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While I agree they are a good cell, they are simply outclassed and not very useful to us.
First. As far as I can tell, A123 systems have not made cells in years. So they're getting old now
2. While I could and have accepted their lower capacity, their lower voltage is a real problem as they don't match up to our uses. They'll blow a lamp made for primary lithium batteries. But underdrive those made for 3.7v cells. They won't run an led light made for 3.7v cells. Not long in regulation anyway and that's only with a very efficient driver and low vf led. In a two x 26650 led light they'll work well, except the lvp will kick in too early.

For replacing 12 lead acid batteries, they're great. But for flashlights, unless it's custom made just for lifepo4s cells, I just don't see them as a viable battery. Not to mention that once again that company has not made anything in a long time. And all the rest of the life PO4 batteries are of lower quality
 

john61ct

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A123 got bought by Lithium Werks, very much still going strong and readily available.

But as the best, of course not cheap.

Also make brilliant NMC pouch cells for higher density use cases.

But the old original cells are still going very strong, if stored properly capacity still well over rated will go for decades more, nothing "outclassed" about them, especially against cells that will only last a few hundred cycles.

None of the above has anything to do with lighting, or any specific use case, of course mostly used in increments of nominal 12V, up to EV levels 400+V

Just talking battery tech in general here

Are flashlights usually low voltage only 1S or 2S?

Even huge ones?
 

vicv

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For the most part. Even the big flashlights generally tend to put all the batteries in parallel.
I did not know that someone took over and was still producing their batteries That's good news. At one point in the quite distant past I built a homemade vape with 2 a123 321140 or something like that. They had a D cell diameter and were twice the length. I could go to insanely low ohms without ever worrying about the batteries.
I really do agree with you that it's too bad the light PO4 tech didn't really continue. Besides the lower what hours they are better in every way. Better cycle life. Lower resistance. Flat discharge curve. And for EVs they would get such better longevity.
 

john61ct

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exactly, why Elon's such a fan, Tesla's been using them in the China made models exported to EU and ANZ now,

to be expanded worldwide production now that Nickel is such a bottleneck

cheaper too and much safer
 
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