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

been using the inr21700-30t in my versapak builds.
so far these are unbeatable in the high demand tools.

33J ? Or 33G ?


Fasttech just listed a BAsen 21700 at 7,58$ :

Bad cell, don’t buy:

Probably economy of scale. To get “volume pricing” on 1M units, a car that takes 500 more-or-less standard cells means getting there in 2,000 cars, whereas with a car that takes, say, 5 Übercells, you’d need to sell 200,000 cars.

(Dunno what Apple cells you’re referring to, so have to use my imagination…)

It is not merely a matter of pushing all the empty space out. That would be nice if it is only a backup storage unit.
It has to be charged and discharged often. That involves (a lot of) heat. So there has to be space, for cooling.

The “old” packs are air-cooled, The newest ones are liquid cooled.

I’m not very familiar with Apple’s electric car, but I haven’t seen anything indicating they’ll be using one big cell instead of many cells like everyone else.

I have had several macbook pro batteries in my hand and also the newer, glued-in variant. The ones I have seen dissected have multiple cells (battery packs) inside the battery. I am not referring to the new, split battery cell design in general, but the content inside the battery. The charge controller is typically on the motherboard and there is another chip on or near the connector where all the temp sensors are (Macbooks behave differently depending on whether battery is plugged in or not).
One of my older Macbook Pros had a “pregnant” battery (bulged out/non-charging) and actually fell apart. There were 3 packs inside, glued together with what I believe was Kapton tape. The individual packs looked like LiPo packs.

edit: the iPhone X battery also seems to have multiple cells

From an engineering standpoint it would be easier to protect future design changes with a flexible, multi-cell battery rather than a 1-battery pack that would have to be re-designed as well. plus all the efficiency/cooling/security aspects mentioned earlier. Imagine a huge, single cell blowing during a crash vs. very few cells in a multi-cell pack.

Phones and high end laptops use LiPO packs instead of cylindrical lithium ion cells.
They are the same thing just in a different shape.
Why tesla uses individual cells instead of lipo packs I’m not sure, it may have to do with cooling since they have to run fluid in between all the cells.

Also one other difference I’ve noticed between cylindrical and lipo cells is that you pretty much never see a cylindrical cell bloat up.
This probably has to do with the fact that it is wrapped in a spiral and sort of holds itself together tightly inside a metal housing.

Just about every other EV manufacturer uses prismatic cells stacked next to each other.

Telsa have pretty much gone their own route for much of the powetrain.

Nissan use a chemistry that is not prone to thermal runaway. LEAF relies on convection cooling and software ramp-downs to keep the battery in safe operating zones. It is less expensive but not as energy dense as what Tesla have been using.

BMW i3 also uses prismatic cells but has some active thermal management.

Google image search will find photos of dissambled BMW, Nissan and Renault packs.

There are also YouTube videos of BMW packs on the assembly line.

Apple doesn’t use “one big cell” they build batteries out of multiple smaller cells, both to reach higher voltages than available from a single cell, and also to make their computers really thin. I think the original MacBook air was the first model to go this route, but Apple has been using pouch cells for a lot longer. Since the first MacBook Pros, at least. I’m not sure when they last used cylindrical cells. I have a dim memory that some of the early MacBook’s (non-Pro) used 18650s, but I could be wrong.

Apple’s long run-times and long-cycle life are not the direct result of using pouch cells. Instead, having the biggest battery possible reduces the wear during discharge. Also, with high-capacity & long runtimes, trading some capacity for increased durability is more tenable. Giving up 10% of a 10hr runtime is a while hour, while 10% of a 5hr runtime is only 30m, but which would be more annoying?

Worth noting, pouch cells, particularly in custom shapes, are more expensive per Wh/Ah than high volume cylindrical cells (ie 18650s)

As for Tesla’s use of cylindrical cells, part of the reason is historical. Tesla was born from the realization that, fueled by the consumer electronics industry, 18650 cells would be a viable power source for high-end electric cars if they could successfully engineer big batteries around them They did. Their first packs were built from basically stock panasonic cells. The cells for the Model S packs was, last I checked, slightly, customized. Their 21700 cell is yet another step in the evolution of their battery tech.

The approach of leveraging commodity cylindrical cells let them launch a successful electric car company and beat larger competitors to the punch, in part because most of those competitors relied on custom battery designs.

Sticking with cylindrical cells allows them to better leverage their past experience. It also allows them more flexibility. They can use the same cells in any car model, custom packs for customers, fixed storage batteries. They can also more easily sell excess production.

ev battery packs must resist to some impactor tests such like a pole . multi cells are just safer.
also multi cells in series are required to reach high voltages necessary for the car motor(s) to run.
think that Tesla is running on 400V motor(s)

That’s not what he’s talking about, he’s talking about cylindrical vs prismatic cells.
Lipo packs used in phones and laptops are prismatic pouches in the shape of flat rectangles, 18650s and 21700s are cylindrical lithium ion cells.
It’s just a different shape.
You can put multiple lipo packs in series just like with cylindrical cells to get high voltages.

Lipo and 18650 isn’t a high or low end laptop thing, it’s a thin versus thick thing. There are plenty of thick high end laptops that have room the room for and use 18650’s, and there are plenty of low end laptops and tablets with lipo batteries.

As far as Tesla, I suspect it’s also because it’s easier to automate at high speed and maintain high quality, in addition to cooling. As far as the latter, just look at the Samsung Note fires due to lipo pouch deforment. A corner got crushed a small amount and caused huge problems. The rigid case and tight tolerances of the 18650 form factor makes that problem much less likely.

Almost every single laptop these days uses a lipo because it is more space efficient, they don’t need any special cooling or durability for the battery.
Old laptops used 18650s almost all the time.
You will also never find a modern phone with a cylindrical cell either.

i want to chime in on 26650
after testing them i think they are Sub-par compared to Sanyo/Panasonic NCR18650

If you’re talking about crappy 26650s then sure, but not a good one like the Shockli 5500mAh cells.
There is no 18650 with that much capacity or current capability.
Not even a 21700.

well i took a chance on this item Aibocn Portable Charger 8000mAh 2.1A Output Power Bank (when on sale for $7.50 and was hoping it might be better then 2x 3400mAh of my NCR18650B

It actually does, rectangles are 100% space efficient, cylinders are not.
You can fit more capacity per volume using rectangular cells.
More capacity = longer life.