Hi, Yes, I'm back at the whiteboard, but more importantly, I'm back at the whiteboard in the old lab. Beauty. Let's talk about Tesla Battery Day, which just happened. And of course, everyone loses their mind every year about battery day and all the innovations announced and things like that.

And there were tons of things announced in this. A lot of people said, oh, it wasn't that exciting, but there was actually lots of cool stuff in here and we're going to talk about one aspect of it. But there were many other innovations in battery chemistry and manufacturing techniques and you know they reckon they undo a 25 000 Ev and like like a ton of stuff. But the one that I wanted to talk about and the one people ask me most about is the new 4680 cell that they're going to actually produce themselves in their Tesla gigafactories.

So I'm going to try and break down why they actually went and designed this new 4680 cell and how it compares to the previous 2170 and the 1865 or 18650 cell that they've used previously. now. Tesla, of course, started out famously, choosing to use cylindrical cells and the standard 18 650 cell or 1865 as they're calling it now because Elon doesn't like the extra zero, it's just in there as a decimal point anyway. Um, they started out using these and then with the model around about the model three ish.

Something like that, they move to the 2170 cell and now they're going to move to the 4680 cell which they've designed themselves. They actually got the pattern back in late November. I'll link it in down below if you want to check it out, but there's not really a huge amount of detail in here. Might put up a couple of graphics from it, but anyway, they've designed this in-house and they're going to manufacture it themselves now.

The big three claims that they had for this new cell was: it's going to have six times the power, and I've circled that one because that's the one that we're going to talk about today and why it's got six times the power over the previous 2170 that they used. It's got five times the energy and it's uh, has an extra 16 percent range in the battery. And quite a few people ask me this: Why If it's got five times the energy of the previous 2170 and you won't, why do they only get 16 extra range? It's all in the market in linguistics, they say energy, not energy density. My density has popped me To you what? I'm your density.

So there's a bit of marketing wankology going on there by having yeah, five times the energy. Everyone sees that, everyone reports it, Everyone loses their collective minds, and well, it's only 16 extra range. So why does it have five times the energy, but only 16 of the range? Well, it comes down to the size of the cells. The 18650 or the 1865 is actually 18 millimeters diameter by 65 millimeters long.

That's where the numbers come from. Ignore the zero on the end. The 2170 they move to is you get to 21 millimeters by 70 millimeters, so a bit wider, bit longer and 46 80 is 46 millimeters by 80 millimeters. It's just a longer cell and thicker.

longer and thick is better obviously. So if you take those dimensions there and you pi r squared H that you get about five and a half times the volume. Hence why five times the energy? It actually should be a bit more than that because they've announced like some new electro uh, chemistry and new material, uh, science and stuff like that they've been working on. which sounds really cool.

so I'd actually expect a bit more than five times the energy. But aha, there's a trick because it's six times the power. So there's actually a big trade-off when Tesla chose to use the cylindrical cells like this. and they're still using cylindrical cells Compared to what's called a large pouch design typically used on most other Ev's I'm not.

I don't think any other Evs use cylindrical cells. do they not 100 sure? Please correct me down below. But anyway, most use large pouch cell designs like this which just have large flat elements in and we'll talk about all the physical construction in a minute because it's important. But basically you're trading off power versus energy density.

Cylindrical cells like this, you're going to get a larger energy density. not a huge amount more, but it's larger. But you don't get the same amount of current output capability i.e power capabilities. So you're trading off energy density versus power between these.

So the large pouch cells, you will get more power out of them, but slightly less energy density. So it's a trade-off but Tesla. Now with this new 4680 cell, they want the best of both worlds. They want the energy density.

Plus, they've got a new Uh Tab or tablets design which allows them to get six times the power out. So with six times the power, does that mean it's like five or six times better than the existing large pouch cells? Well, no, not really. You have to actually get the both which have the same energy density and do proper apples to Apples comparisons before. you know that.

And really, there's not going to be a huge amount and a difference in it, but they have actually increased the power per capability per ie. current. Think of the current capability per cell compared to the 2170 and this all has to do with the tab design. So if you take one of these cylindrical cells here and you unroll it, this is called the jelly roll.

Then you end up with basically our three strips of material in here. Now, the layer that I've drawn on the top. Here, This is the conductive cathode that's the positive terminal and that actually is coded with the lithium. Whatever material.

whatever the latest whiz-bang material science technology they got in these different performance, different energy density requirements and different thermal properties and all sorts of stuff like that. Choose all these different cavities, choose your flavor. Anyway, it's a Lithium-coated conductive uh plate on there, and in the case of the 2170 cell, uh, somebody's taken one of these apart and actually looked at it. It's about 800 millimeters long, so you know it's fairly lengthy.

It's like the length of my arm and this sheet I've drawn on the bottom here. Uh, this is the copper anode. It's usually made out of copper. It's usually quite thin.

Like, you know, you won't get much smaller than 10 microns. It can vary, but that would be the sort of like minimum thickness that you get in there. Once again, it's a trade-off of energy density versus power. The thicker you make all of these layers in here, then the less surface area you can get.

Therefore, the less energy density. But the thinner you make them. especially like the conductive layers, the thinner they get. Just like on your Pcb, you get one half ounce copper, one ounce copper, two ounce or four ounce copper.

Something like that. It has a lower resistance and we're going to get into that, and that all has to do with the ultimate power output or maximum current output capability. so we don't actually know specific details of the 4680, whether or not it actually uses thicker, uh, conductive, and copper materials in here, but the six times power output actually comes from a different tab construction, I'll talk about that in a second, but we've got the final layer in the middle, which I've drawn in green here, and that's the separator that actually is a porous material. and it's usually some sort of Poly.

put the kettle on uh, material like that and it has to be porous uh to for the chemistry to actually happen. And uh, the neat thing about uh, some of these Poly materials used in these, even though they're porous effectively, you can think of them like they've got little holes in them. Uh, then when they actually when these batteries overheat, then this, uh, poly put the kettle on material can actually melt and it can actually seal those holes. And that actually stops current flow.

And they can sort of like self-extinguish It's like a overheating protection mechanism. It's kind of cool. Don't know if the 4680, you know, has that or the existing 2170. Not entirely sure, but anyway, that's just a cool feature of the separator.

And for those playing along at home, the poorest percentage I.e how porous it is, you know it's around about 40 to 60 percent. sort of. you know, somewhere in that range. Now I said that.

the copper anode down the bottom, the negative terminal, that's always pretty much always copper. and I believe it is the case in the Tesla shells. In fact, that's what they show in the really sexy, pornographic photo that they've shown for this thing. It's just look at all that copper.

Oh beautiful, Beautiful. But I specifically said that the cathode at the top here is not going to be copper. and I won't go into the reasons why it's to do with the electrochemistry of it. And well, so those battery cell chemistry experts can debate that down.

uh, below. But it's usually like a aluminium something like that and which is coated with the Lithium uh type material. And now this is where the magic in the new 4680 battery comes from. It's called a tablet design and this is what they have the patent on and you can see that basically all exist in cylindrical cells.

They actually use these welded tabs. They've got a tab on the top layer and a tab on the bottom layer and you see these little dots in here. These are like the little, however, they want to weld those on so they've actually got to weld those onto the top and bottom. and then the tab.

Actually, then that's got to be welded to the bottom. Uh, battery to the negative battery terminal. This one has to be then welded up to the positive battery terminal. and well.

you've got all these little connection steps in there. So Tesla, of course one of their big announcements is they want to be the World's best manufacturer. Just the world's best manufacturing company. So they're optimizing their steps and they've got some.

You know, really cool technology. And this tablet's design is known not only to give increased power, but it's also to reduce production manufacturing steps as well. Because if you've got to produce your jelly roll like this, you know you've got to coach your aluminium cathode up here. And then you've got to put your signal and manufacture your separator.

And then you've got to roll it with your copper anode and stuff like that. and then you're going to stop or move to another part of your production line and then weld on these tabs and it's just like horrible wastage production steps. So what they've come up with is a tablet design. To do away with these tabs that not only improves manufacturing speed and streamlines the whole process and things like that, allows for, uh, more automation.

You're less machines. You can install more machines per square meter of uh, factory space and all that sort of great stuff which they're working on. which was one of the huge announcements by the way was that I can't remember the exact number like order of magnitude saving in battery manufacturing floor space or something ridiculous like that. It was really quite amazing.

So as I said, when all these layers are all rolled up together, this is called the jelly roll. Well, I got the dunny roll. uh, to give a demo. so let's have a look.

Just so. just imagine that this is your cylindrical cell. I've got little, uh, post-it notes on here for the tabs. so if we unroll this sucker here we go.

You know, roughly 800 meters. Good enough for Australia, right? You've got the tab over here and you've got to tab it down here as well. This will make an interesting thumbnail, won't it? Um, imagine that you've got your copper conductive surface like this. Your electrons.

You know they're being produced. You know, Everywhere all the way along here. And they have to travel the whole length like this. They have to travel the whole 800 millimeters to get out.

That's a long way. Please excuse the crew to the model. Didn't have time to build it, scale or to paint it. I think I'm going to come a gutsy here.

I put some post-it notes, but what if you had lots of tabs? like covering the whole thing of this when you roll it up like this then I should have made should have ripped off more of the Dunny roll. But what if you did that and then you folded all of the tabs in like that? Is that looking something like the Tesla photo? Not really. but hopefully you get the idea. that's what they're doing.

This is called a tablet design, but Dave, you just said there's like all these multiple tabs. What if on your copper anode like this, you did away with the tab like this like that, and you put all these little cuts along here like this so that then you could like fold them up and over like that. Every single one of these, then the entire length when you roll it together and it rolls inside like this. Okay, and then your tabs all like fold over into the middle like this.

and this is exactly what we're seeing on the Tesla Well Design. Yeah, I really didn't have time to build this to scale all the paint, did I. But does that look something like what Tesla have shown? Yep, that's exactly what they're doing with the bottom anode. here.

They're actually cutting it in the one sheet of copper, doing away with all of the tab worlds. And this has some really cool advantages. And this is how they're getting the six times power output. So why are we getting six times the power output? Well, in this particular case, let's just extend that out.

Let's imagine that's our battery like that. All of these tabs are all folded over on top of each other, so you're effectively shorting out this whole bottom. So instead of your electrons having to go the full 800 millimeters, they only have to go the maximum of the 80 millimeters, which is the height of the cell. So at most the electrons just have to travel the 80 millimeters instead of the 800.

you've just lowered your resistance. Everything else being the same, lowers your resistance by an order of magnitude. And when you lower the equivalent resistance of your cell, you can get more power out of it because there's less power loss. There's less I squared r losses.

So if we plug some typical numbers into a calculator here for as I said, a 10 micron copper sheet, I don't know the exact value for the Tesla one, but let's just put 10 microns on there. You wouldn't go any thinner than that, especially for a high power application like Ev batteries. Then if you whack that into the calculator, the number that pops out for the 2170 up here in the 18650, they're roughly equivalent. Uh, you know, in the order of 20 milliohms cell resistance Like maximum when if the electrons have to travel that whole 800 millimeter length.

But you plug the same numbers into the 4680 up here. Bingo because it's an order of magnitude shorter distance like this for the same thickness of copper, and hence like to say assuming that the chemistry is the same, everything's the same. So the energy density of the battery is the same. remember that word density.

The electrons now only have to travel the 80 millimeters like this instead of 800, so therefore, it's an order magnitude less resistance. It's going to be in the order of like two milliamps, couple of milliohms, and that is equivalent to the here's some actual Uh data for research data that's equivalent to the large pouch designs which are used in other Ev car batteries, the big flat designs, and the reason the large pouch designs have very low resistance in the order of a couple of milliamps is because they're physically large big flat sheets like this, and the tabs come directly out. Um, there's you know, like there's none of this roll rubbish in here that you got in the 2170s and the 1865s. And then if you really want to the pouch designs, you can actually put more of them in here like this, and then you can just fold the tabs over similar to what we do here, and then you can.

Or you can, just you know, like bust, bar them like that up the top or whatever. and you can get very low, equivalent series resistance for the cell. And that's what Tesla are trying to do here because they've realized that their choice of the cylindrical cell limits them in power. And of course, Tesla are like massively powerful cars, right? One of the most powerful on the market.

So why do they need to make six times more power up here? Well, they've got the truck things coming, but also to do with the thermals and the losses. So if you look at their existing cells, which we're getting in the order of tens of millions, serious resistance. Let's say it's drawing 10 amps here. That is an internal power loss of 2 watts, right? 20 milliamps times 10 amps.

That's 2 watt loss. And for a typical you know, lithium ion cell, that might be the equivalent of, say, you know, five percent loss in the cell. So you have that internal heating in the cell and that can affect, uh, the performance of the cell. But yeah, so you've got to get all that heat out.

and really, um, you know that is quite a lot. So the existing pouch cell designs large pouches are much better in that respect than the Uh cylindrical cells which Tesla chose to use. Why they chose to use that originally I don't know. it was cool, and they're off the shelf.

They wanted to sort of use like off the shelf 18650s and it's worked for them. But their thermal management of the packs has been quite different because now we have to talk about the thermals a bit. So when it comes to heating up and thermals of a cylindrical cell, it's what's called anisotropy, Which means that the heat is basically in the axial direction like this. If you look at a heat map of I'll put up a heat map over here of a typical prismatic cell and how they heat up inside, you'll notice that it's in the axial direction like this.

and really the best way to extract heat from a cylindrical cell like this is from the top and the bottom. It's going to have a higher thermal resistance if you try and get the heat out of the sides of the cell like this. it's just got higher thermal resistance. So this is what Tesla have done in the past to cool down their battery packs they've relied on like, actually, you know heat, conductive materials and things surrounding the you know, the sides of the cell like this.

and it's not a very efficient way to cool down prismatic cells. They want to basically get their heat out in an axial direction like that. But the problem with the existing cell designs is that, well, look, you've got this bottleneck. You've got this tiny little piece ant tab down here.

little thin little tab coming out here and here. that's a choke point that's massively high thermal resistance trying to get there. Sure, you might have this big slab of copper in here, right? 800 millimeters by 70 millimeters or whatever. It is, right, and like huge amount of copper in there.

But then your bottleneck trying to get it out the bottom or even get it out the top. Ah, Coppers, it's going to be better to get it out the bottom via the copper terminal. By the way, it has to go through that little tab. Not a very good design, but with the new 4680, they've solved that because they've folded all of the copper over to have one big huge chunk of copper coming out the bottom of this thing.

So that's how Tesla is going to cool these new batteries. They're going to get them all out the bottom like this. It's going to have a massively low thermal resistance because it's in direct contact. Well, it is direct contact.

They've actually their bottom plate. If you have a look at the patent here, it actually shows that the anode uh, plate down here has like these little spikes on it that I don't know if they'll actually use that in production. Um, but you know it's basically going to have contact stitch, which then, uh, contact with this huge, basically one big copper sheet like that. And basically you're getting all of the heat out very efficiently via the negative terminal of the battery.

So that's how they're going to cool down these designs. It's going to be a vast improvement in thermal efficiency compared to the existing uh, Prismatic cell the 2170s in the 18650s. So if we go back to our copper resistance calculator and we plug in the numbers for the 4860, you will find for the same 10 micron. In fact, it's 9 micron because that's what my calculator has got.

But you know, good enough for Australia 9 micron copper thickness. So we're comparing apples to apples. Between the 2170 and the 4680 here, it's an order of magnitude lower resistance as we said before, and uh, so our power loss. Our internal power loss at the same 10 air nominal 10 amps.

Then we're talking 0.2 watts instead of 2 watts. So not only have we drastically decreased our thermal resistance to extract the heat out of the battery the correct method how it should be for a Uh cylindrical cell, but we've also lowered the internal resistance of the cell by an order of magnitude as well. Double Whammy. It's great.

So this is how they're going to get the six times power output of this thing. As I said, the energy uh in there is just due to it being a larger cell. They're going to get 16 percent, uh, plus rain. So I'm not hugely impressed with the extra uh 16 here.

I I think they'll get uh better. like longer battery life. You know they didn't I don't think they didn't announce their million mile battery, did they? Everyone was kind of expecting that, I think. But yet, you potentially get uh with the better thermal management of these cells.

And simpler as well. Because you can just have one gigantic bottom plate on the bottom of the battery. you don't have to run all the crap in between all the cells and get it out inefficiently that way. Just one big huge heatsink on the bottom that you know you've only got the contacts.

Basically, you're getting the heat directly transferred via the copper to this huge base pad. Here, you will have, of course, some thermal contact resistance between the internal copper sheet in here of your jelly roll and your negative anode terminal down there. So those little spikes or whatever they're going to use, so there's some little contact resistance there. But it's still vastly improved over the existing Uh 2170 design.

and then you'll have that negative anode terminal basically, just you know, pushed straight against the heatsink on the bottom, and they'll use that as the conductive uh thing as well for the cells. So and then you'll well, you've got to like insulate it and stuff like that, so they might have some like, you know, conductive thermal insulation and stuff like that. But anyway, it's going to be vastly improved over the existing 2170 design, so almost certainly they're going to get better range, better life, all sorts of things out of their battery, and simpler thermal management. It's a win all round.

And you might be asking, Well, it seems really obvious, why didn't anyone just cut these? uh, you know, instead of welding these tabs onto here, why didn't they actually? um, just cut the copper before and then fold it over? It seems like a really obvious thing to do. I don't know. comments down below. So there you go.

I've waffled on enough about the 4680 cell, but hopefully you learned something there about cell construction and thermal management and stuff like that and battery construction. But the good news is that the new 4680 cell is basically in that has the same internal resistance as the Uh large pouch designs used by other manufacturers. so in theory like the power should be like very similar how it works on like energy density and stuff like that and versus weight and all the other stuff you can put into metrics for the for electric vehicles and uh, performance and stuff like that. But anyway, yeah, they're now on par with the large Uh pouch designs and that's really cool.

and in terms of thermals, probably equivalent as well. although you know once again, you got to do a proper Apples to Apples comparison. It might be quite hard to compare them thermally and things like that. But anyway, fast improvement and just go to a bigger cell like this as they did for the 1865 to the 2170.

just moving to a much bigger, fatter cell like this, you get just inherent advantages just by doing that. Regardless of any other technology changes at all, you get uh, increased packing density. Uh, of course because you've got like a larger cell so you'll have like of the energy density per cell is going to be larger. As they said like five times or five and a half times the uh energy.

Just by going from this size cell to this size cell, you can pack them all together and then you've got uh, the steel casing as well because you've got to have the steel casing on the cell. so potentially lower weight there because there's less steel in individual, you've got fewer cells. So for the same given kilowatt hour size pack, uh, you've got like, just a lot less metal in there, just so it's got a way less that's going to be an inherent advantages. You've got manufacturing fewer cells on your production line, so there's got to be inherent advantages there.

just just sheer like manufacturing, Handling and stuff like that alone would have advantages. So lots of advantages in these cells just by moving from that to that. So actually ignoring all the other uh, you know, the tablets, design news, and the other material science technologies and different uh, stuff they're working on, it's actually rather these numbers are actually rather disappointing because as I said, I expected a 5.5 times. Just do the calculations Going from this size to this size, it's 5.5 times the energy anyway.

like Whoopty Do Um, you get that by going to a larger cell and 16 plus range. I haven't run the numbers, but here's an exercise for those playing along at home. Uh, just you know. calculate the extra like, uh, volume efficiency, volumetric efficiency you'd get when you like stack all the cells, uh, together in a flat pack.

How much extra range you'd get just by actually increased efficiency of the packing density of a larger cell versus a smaller cell. And you'd probably be surprised if it's not near 16 anyway. So really like. The only exciting announcement here is the time 6 power due to the tablet's uh, design.

But apart from this, um, it's It's rather disappointing actually, because you get that anyway by going to a larger cell. Ah, so there you go. I hope you enjoyed that. I hope you learned something useful.

And if you did, please give it a big thumbs up. As always, comment down below and check out the Eev blog forum where no doubt everyone's going to discuss this. Catch you next time you.