Will the 21-70 Battery (a.k.a. 21700) Replace 18650?

kmart will be long gone before 21700 are out there in any great numbers.
most folks around me already have 18650 and even their kids use them now.
as for vaping lots of lipo powered mods out there.
i have a vicious ant and a sigelei here that use them.expect them to become much more common.
genie is out of the bottle already as walmart carries 18650 and flashlights that use them.
adapting to 21700 if they become cheap and common will be a simple production change too.
i doubt 18650 will go away anytime soon with all the power tool mfrs heavily invested in the format.

I’m with the other posters that want to see 21700 batteries with >= 5Ah capacity, and I think the markets will take notice.

I’m pretty sure 18650 will be around for quite some time, and I sure hope I’m right. I’m not sure the current 26650 size will survive.

Right now I just want high capacity 21700 cells that I can get my hands on and I’ll enjoy the ride.

We may see a 5300mAh cell (INR21700-53G ?) from Samsung by 2020, or earlier.

I don’t think most of you are realizing whats occurring here. It is a sea change which will upend whats going on with something entirely different. It’s not that this new 21700 cell is a different size or even better. It is going to change the world. Not because it is a 21700 instead of a 18650 and size matters (ask my wife- wait, nevermind). They will be powering battery banks for houses and factories the same way that the 18650 are powering some cordless tools today. Solar arrays will be charging these battery banks all day and at night you will be able to run your home and recharge your car (same cells) off them. It isn’t just Tesla that will have them. Every EV car and E device will as well. Not just because of size. That Tesla says this is the optimum size is critical to industry acceptance, but because the future will see X3 the power and then later even more, from that size cell. There are multiple streams of R&D working to make them better, along with every major mfg of energy will be working on making them better. To last longer and pump out more power. Faster better quicker. This is huge like we haven’t seen since Edison started to wire cities for electricity. 21700 is the future, as sure as the sun will shine tomorrow. But isn’t not 5000 mah that is in question, but if 10,000 will be there sooner than we can conceive. It ain’t about flashlights. It’s about the world.

Please don’t ask me for a timeline. If the middle east crashes tomorrow, I’d say “sooner’ If they find another Bakken, I’d say ”Later, much later”. It’s coming, and in a big way.

Battery banks for houses use SLA batteries because it is much cheaper for larger capacities.
Batteries for EVs are made from LiFePO4 prismatic cells which have far more charge cycles and more stable voltage curve. They also take up less space than cylindrical cells.
I contacted battery manufacturers for EVs and they have stopped producing more of their large scale cylindrical cells in favour of prismatic.
21700 will never become popular outside of tesla vehicles.

don’t Li-ion have higher energy density then LiFePO4

Very interesting assessment ‘Couchmaster’.
You may very well be on to something, what you say makes a lot of sense. :+1:

One thing is certain…. time will tell. :wink:

The chemistry might in fact turn out to be something entirely new. There are a lot of companies, not just Tesla, tossing large money and a lot of high quality personal at the problem of optimizing power storage in these cells. Tesla was in a race to get product finalized as the development of the batteries was about to head on crash in a race with the development of the gigafactory. They didn’t just try to change the form, but the function as well. They were still testing new cathode material a few weeks before the production was to start I had heard. I suspect that the product they are producing now will be tweaked, modified and improved on a continual basis. I’d love to see a Tesla engineer/chemist share how that went down.

But the Obama administration has also placed a lot of bets on energy via grants. I don’t know what the next administration intends as far as those go but would expect a lot of continuation. I doubt there is a comprehensive list anywhere in the world of everyone who is working on this issue.

Yes, but only last hundreds of cycles compared to thousands for lifepo4.

For something used as often as a vehicle it is nice to not have to spend $5000 on a new battery every few years.

Some test results, at 20A, 30A, and 35A, for the Samsung INR21700-30T can be found here:

http://www.mountainprophet.de/forum/viewtopic.php?f=16&t=952&sid=2cc2ee9ac938b85f5ecec01273ccb428

In this mini test, it was compared to a Sony 18650 VTC5A and a Sanyo 20700B.

HKJ has posted his more thorough test of the Samsung INR21700-30T:

An impressive battery at high currents.

The thing is it is not just a size game, 26650 never got the attention it need from manufacturer hence it relatively low capability, in theory it should perform much better in capacity and amp draws compared to 18650 but look how much more capacity we gained from 26650? The new Sony 21700 3Tron should be around 5000mah that is as big as 26650 capacity-wise why? because that is where manufacturer now put their research/effort on. So if they leave the 18650 and focus on 21700 i think it is in our best interest that we also starting to use 21700 as a 18650 replacement. As the development on 18650 will be secondary.

Springs can take up the 5mm slack along the longitudinal axis, and all anyone needs to do is make battery-tubes bigger by 3mm (1.5mm “wrap” would take care of rattling 18650s).

The same way a tube that takes an 18350 can also accommodate 16340s with a little slop, the same can be done for 18650s vs 20700s/21700s.

Don’t want rattles, a bit of construction-paper wrapped around an 18650 can cure that.

Don’t see what the problem is, just need flashlight mfrs to get on board.

Assuming it’s true, it’s still not as high capacity as 26650 (5500 mAh Shockli), but is nevertheless more efficient on per-volume basis. On par with 18650. And really looks like a great choice for pocket rockets.

You do realize that this graph still shows “hundreds” of cycles, not “thousands” right? :wink:

Somebody mentioned flashlights that come with 3×AAA adapters. They are a bit larger than 18650, aren't they? Would 21700 fit?

Personally, I prefer 26650 size over the thinner 18650. If large efforts are put into developing 21700 cells with >4500mAh, then those would be better than 26650 in every way. This is what I hope will happen

The formula for fitting 3 small circles with diameter d in a bigger circle with diameter D is: D = d * (1 + 2/√3).
Or to put it in plain numbers: D = d * 2.1547.
Because the diameter of an AAA cell is 10.5mm, you need 22.62mm for an AAA adapter to fit in.
That should be enough for a 21700 to fit in.

Yes, but they will obviously last that long since they have retained so much of their capacity after hundreds of cycles. Even the worst one is still above 85%!
The main thing that makes a difference is not fully charging them and not discharging them all the way to 0%. The other thing is the active cooling. They never get hot.

But AAA is 26 mm too short, which adds problems of its own. Nevertheless, good call with 3xAAA.

The AAA carrier makes up the difference in length. I have several lights that take AAA or an 18650. They should also work fine with a 21700.