Not sure that’s true. I’d scribe a unit circle in a unit square (L = D = 1), and the box scales up and scales down equally. With twice the diameter, you’d have 4 unit-squares instead of 1, but the ratio of space-to-stuff should stay identical. A cylinder would just stretch that in a 3rd dimension.
Packed in a zigzag fashion, you’d only have something different for edge-cases around the periphery.
I think more important would be the rather fixed thickness of the walls of the cells (ie, an AAAA won’t have a foil-thin wall), there’d be more active material in the bigger cells. Ie, by analogy, a jumbo box of cereal would be much more “efficient” vs a trial-size, considering the cardboard of the box is the same thickness in each, so the cereal:cardboard ratio is much higher in the jumbo box. Pretty much, the same goes for any packing material.
Plus, fewer connections total for fewer-but-larger cells, fewer protection circuits, less overhead in tops (even flattop caps), and so on. Otherwise, a nest of 10440s would be most efficient.
Considering how much of the batteries we use (high discharge 18650s) are greatly driven by the power tool industry it probably depends if they want to make the jump. Or rather if battery manufactures try to get them to by offering high discharge cells in that size. Considering so many power tool companies seem to want to sell different sized battery packs, from tiny 1p setup packs to large 3p packs. Maybe they’ll keep the 18650s for smaller packs and use these for larger ones. I know I’ve seen at least one power tool pack with 26650s, I think they were probably the older sony ones if I recall. It’s not that hard for them to switch toolings since its just some plastic molds that they replace anyway with new models and styling so it depends on the battery companies to offer cells they can use and in turn they will bleed into our market.
I think Tesla has a pretty good chance of sticking with these cells for quite some time, they’ve done the math on all the volume and cooling issues and that would only change if a significant improvement was made. Look how long 18650s have been around, they’ve probably advanced far more then lithium based batteries will in the near future. We are running out of improvements with this chemistry it seems. But who knows maybe they’ll just switch to some other energy storage system.
A couple folks here think that the flashlight industry has any influence on 18650 production. It’d be nice if it were that way, but they don’t care about the flashlight industry.
This is the only other industry that matters now that the laptop industry has been moving away from 18650’s. The only thing really stopping them from switching is the necessity of having to get new injection molds, that, and the availability of 21700’s.
Other Gigafactories are expected to sprout up around the globe, and Finland has already applied for one. Other companies are going to be hard pressed to ignore what’s becoming the biggest industry and customer of prismatic lithium ion batteries. Look at what the 21700 allowed Tesla to do to the capacity and price of the Powerwall 2. Why would other users of prismatic lithium ion cells, like the power tool industry, use more expensive cells if they could use the 21700 to lower costs and increase capacity?
I would even say for many of us, laptop development has been pretty unimportant for some time now. I guess it depends on what types of lights you buy and build but the high capacity low discharge cells used in laptops don’t interest me much, I want cells that can dump stupid amounts of power without much voltage sag.
Also the “laptops are here to stay so we’ll have 18650s from that industry” thought I’m not so sure of. Sure I think laptops with keyboard will stay but many of those are becoming “convertible tablets” “netbooks” etc that while they have a keyboard are made to be too thin and too compact for 18650 batteries.
What i am basically saying is that because Tesla is going to use 21700 does not mean 18650 is dying
Unless it catches on or Tesla sells to everyone and puts serious competitive pressure on other manufacturers to phase out 18650s they are in little danger.
Keep in mind we already have other form factors, 14500, 10180, 26650, 32650 etc. None of them decimated 18650.
You need space in between them no matter what for cooling and I’m guessing they just thought the construction technology had so many advancements to cylindircal cells there wouldn’t be much gain to making prismatic cells with some cooling array setup.
Oh I don’t think that they will go away at all but we may see the “big guys” slow production and development in that size particularly for high discharge cells. We have all sorts of different sizes but because the development has been behind the 18650, the 18650s still crush everything else in power density. Even the best 26650 is nowhere near two good 18650s even though they are the same total volume. This is across the board, we don’t have any 7000mah 26650s and we don’t have any 60A 26650s that sag less than 2 18650s at 30A.
I’m dreading this post already. The 18650 is the biggest Lithium-ion cell manufactured outside of China. I can’t find any in the last 5 years made outside China. This is why top end 26650’s act like the average Chinese 18650 on energy density, same technology. So Tesla engineers take out the slide rules and determine that a particular size gives them the very best edge. They don’t care about the laptops, they make cars. They don’t care about power tools, they make cars. They don’t care about FLASHLIGHTS, they make cars.
I’m guessing their engineers looked at cell density, shell thickness, heat removal, how many connections are needed. Things that engineers with clean slates dream of. I’m pretty sure none of the previous engineers looking at laptop and power tool design thought “What are the flashaholics going to do?”
Now what does a true flashaholic do? He says to himself “Now, what can I build with these?” Flashaholics take whats at hand and exploit it to the fullest.