4680 Thermal Design and Management // Why Ribbon Cooling is Better
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- เผยแพร่เมื่อ 31 พ.ค. 2024
- This video covers the thermal design and management for the 4680, how the tabless electrode helps, and why ribbon cooling is better. A battery pack is only as good as its weakst thermal link.
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Dirty Tesla on Cell Failure of a Tesla
• What Happens When a Te...
Prediction of Thermal Issues for Larger Format 4680 Cylindrical Cells and Their Mitigation with Enhanced Current Collection
iopscience.iop.org/article/10...
Optimal cell tab design and cooling strategy for cylindrical lithium-ion batteries
www.sciencedirect.com/science...
Surface Cooling Causes Accelerated Degradation Compared to Tab Cooling for Lithium-Ion Pouch Cells
iopscience.iop.org/article/10...
Cell-matching and balancing (Battery University)
batteryuniversity.com/article...
Timeline
00:00 Intro
00:50 Why is Thermal Management Important?
01:09 Battery Pack // Weakest Link
02:08 Cell Matching & Battery Management Software
03:43 Battery Cell // Weakest Link
04:23 The 'Thermal Supply Chain'
05:40 Nissan Leaf vs Model S
06:05 Thermals and Form Factor
06:57 Cooling // How I got it Wrong
14:03 Role of the Tabless Electrode
18:48 Current Collector Plates
19:42 Summary
Intro Music by Dyalla: Homer Said - วิทยาศาสตร์และเทคโนโลยี
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Kudos to you for being transparent about being wrong in the past, and correcting it.
100%
Totally, this gives Jordan huge street cred!
Keep up the great work. If your understanding changes/improves we all win!
You mean, not anticipating that Tesla would go with a legacy technology ;)
Jordan’s intellectual humility personifies the difference between scientists and Wall Street analysts - who are never wrong about any thing at any time …
One Factor that doesn't Limit my appreciation of this channel is Jordan's transparent willingness to admit what predictions he got wrong and why. In a world of influence and fakery, this is both factually invaluable and appreciated. Astonishing to me that the Channel doesn't have a million subscribers.
It makes the journey a bit more interesting when you screw up, lol. Not that I plan on making a habit of it.
@@thelimitingfactor
Wouldn't exactly call it a "screw up"!
@@thelimitingfactor Musk would approve that you are pushing the limits, taking risks. Science is about being less wrong, about useful predictions, understanding. Full credit to Tesla engineering team for being totally amazing.
@@thelimitingfactor Seriously nice information, I'm gonna become a patron. This is gold.
Amazing to see Tesla chose the correct form of cooling since the beginning in 2012. The power of first principle thinking.
Thanks once again for your insights. Surface area of contact with the thermal sink is the key determinant of sink efficiency. That makes sense. And the tabless design reduces resistance and thereby reduces point thermal spikes, thermal heterogeneity, and accelerated electrode failure.
Great summary!
Actually NO! Your last sentence is accurate but your take on 'Surface area' efficiency is 'out of context' in this case.
When 'all other things are constant' (heat sinks being equidistant from the source etc) then contact surface area makes a difference. However, the Top & Bottom plates are much closer to the heat source (current collector inside the can) than '1 rectangular patch on 1 side'.
The video's take that Top-Bottom cooling somehow 'orphans' the sides is ridiculous. Most heat will flow from current collectors to the 'infinite-tabs' connected to Top-Bottom caps....leaving very little to flow thru the dozens of insulating layers leading upto the side walls.
Let's assume that heat from current collectors somehow permeates to the sides (in large quantity), then if side walls can wick heat from the Top-Bottom to provide efficient (?) cooling (as described in the video), then it's only logical to expect the reverse flow (that Top-Bottom will also be able to wick heat from the side walls).
Net-net, Top-Bottom cooling of 4680 will always be more efficient than (one) side cooling. However, the choice made by Tesla might have been driven by other considerations (like safety....ability to vent a thermal runaway via the bottom etc). Even though Top-Bottom cooling maybe the MOST efficient, the side cooling (via ribbons) may have achieved REQUISITE cooling while providing design flexibility to take care of other aspects (safety against thermal runaways etc).
Note that Top+Bottom cooling means heat is wicked away via all metallic contacts. Side cooling ( or for that matter Top-only or Bottom-only) essentially means that one set of current collectors are directly cooled, while another set of current collectors have their heat wicked thru the insulation material to the adjacent current collector of opposite polarity).
(Also to be noted is that Top-Bottom cooling that facilitates a more pristine honeycomb packing will also be structurally MORE strong. But again, Tesla might have attained REQUISITE strength in the current design that they felt comfortable to heed to other aspects viz safety)
I recall Sandy Monroe stating, about a year or two ago, when the 4680 was first being mooted that he felt the power dissipation aspect of the 4680 was the most compelling part of the design, even before any particular chemistry. And this video supports that view.
Great video. I was also under the impression that plate cooling for cylindricals was the best approach. Also worth mentioning that teslas 4680's uses ~600 micron cell cans, which would greatly increase the thermal conductivity of the can itself
Can you help me understand this better? Are you saying that something about the outer cell wall thickness makes side cooling better/worse? As I understand, the "structural" 4680 can is thicker than traditional cells. Doesn't thicker wall slow down heat transfer? Or are you saying the cell side wall thickness much thinner relative to end cap thickness? Just trying to understand how wall thickness plays into the system.
@@oof_Dad good question.
What i meant was that the added thickness (for structural reasons) (compared to other cylindrical cells) helps with thermal transfer as you've got a larger number of atoms which can transfer the random kinetic energy throughout the entire cell can body, despite having the source of the heating/cooling being further away.
Usually, adding material would increase the thermal mass and slow down the temperature change. The kinetic energy transfer would still be the same, but the temperature change per unit kinetic energy gain/loss would be lower. The less atoms you've got, the more kinetic energy per atom, and thus the higher the temperature gain/loss per unit kinetic energy added. Energy stays same.
However, the added thermal mass in this case is negligable, meaning that the only appreciable effect would be that of a greater thermal transfer capabillity. By having thicker sidewalls (as a result of a thickner can), you increase the thermal transfer to the entire cell body.
There is something soothing about your voice that it help me fall asleep in the evening 😅
😄 Quite common.
Along with the structural benefits of ribbon cooling and the fire mitigation benefits, it is just a much more feasible manufacturing task than assembling hundreds or thousands of cylindrical cells in a bottom cooled pack. Especially given the need for standard separations between cells and placement for the collector connections, it is just much easier to glue the cells to a ribbon cooling tube and make bandoliers then to place hundreds of loose cells into a pack precisely and try to assemble the pack from there without jostling them out of place or tipping them.
Very interesting. I was under the impression that plate cooling was superior due to those plastic separators so the nuance is much appreciated.
At @15:15 you state that the heat dropped by about 60%, which is correct based on the math shown. But at @15:30 you multiply by 0.6, which would be only a 40% reduction. You should have multiplied by 0.4, or divided by 1.6. The conclusion you reached was that heat losses come down from 5% to 3%. But the math would bear it out that you go from 5% to 2%. While that's a 1% difference, the difference between 2 and 3 is 50%.
Great video so far, loving it always.
Thank you!
Sure thing Paul!
It’s possible there is also another couple of benefits to ribbon cooling. The ribbons can act like a stiffener to the battery pack, providing internal support. This in turn reduces amplitude of vibrations, which in turn reduces forces acting on the battery connection. Ultimately providing better longevity of the pack.
Where does this assumption come from?
My first Job after school was as a sheet metal worker. Square ducting is often folded diagonally to increase stiffness and reduce noise. Noise is vibration.
A straight ribbon would be floppy, a formed ribbon will be stiffer.
Bingo! Thanks for your thoughts
Something nobody seems to ever mention is the relative simplicity of the manufacturing equipment required to make large cylindrical cells compared to pouch types. The simpler the equipment, the more reliable and the cheaper it is to produce. It's also easier to ramp up the production rate than all of the stop-start motions and complex alignment moves required for pouch cells. I really can't see Tesla changing from a simple to a complex line which much surely take more factory space, even if there are marginal gains in other areas. Elon keeps saying that the product is the factory, and the large cylindrical cell format fits that narrative perfectly.
I've mentioned it in the past. But this video isn't about the cell manfucturing cost.
It's the basic principle.
Large amount of GWh (TWh) from the smallest possible factory.
Jordan your knocking out videos with the quickness! Love your stuff! Keep up the great work!
Small correction LEAF batteries aren't actively cooled, just passive heat transfer, 1rst gen Ioniq is example of active air cooled battery
I don't think I mentioned active or passively cooled. insideevs.com/news/482245/nissan-leaf-repair-liquid-cooling-benefits/
@@thelimitingfactor "The first generation Nissan Leaf was air cooled"...
All generations were convection cooled. Only the Nissan e-NV100 was fan air cooled.
Excellent stuff ! I had to specify and manage the battery "fleet" at a robot company. So batteries are eternally fascinating (to me !) . One thing I suspected, and AI2 sort of proved, is that Tesla's ability to model the real world is unrivalled ( nobody really mentions this rather important moat). That is a mix of software, mathematics, physics and engineering expertise, to model whatever they need to optimise - rather than rely on "expert opinion". What's interesting here is the "bias towards the proven result" - once you realise the reasons why side cooling is better - "Well it's obvious! "...(except it wasn't at the time...)
Amen!
Thank you for all the work you do for the Tesla community 👍
Well done. Thanks Gordon.
Regarding Thermal function of the top/bottom Plates. My take is because your Tested 4680 Cell was not used under pressure, in a car, prevents us from seeing the Actual affect of heating cycles. Hope that @Munrolive will dissect one.
With base plate cooling, the cans are attached to the cooling plate rather than a structural plate. I imagine the latter yields better structural strength/rigidity.
A very illuminating explanation... confirming also that Tesla's engineers considered all possible functions (thermal, electric, structural, ...) of every part in order to improove vehicle's efficiency...👍🤙
I definitely think that the thicker casing of the structural 4680 cells will help spread the cooling more evenly around the entire circumference of each cell, helping to negate the increased ratio of diameter to length found in the 4680 (as well as the structural benefits).
What a surprise ,I was sure it would be done at the copper anode end of the sell, it goes to show how clever Tesla truly is, Thanks for your update .
Incredibly informative and easy to understand. I'm not a chemistry geek, so there are times when the explanation flew over my head. But overall, it confirms my faith in the 4680 battery, especially if the Tesla owner plans on keeping the car for a long time
Awesome breakdown, thank you. Here in southern Appalachia we heat exchange with our stills the same way, copper tubing with max thermal exchange through the walls of the tube, not the ends. ... . .
This is amazing analysis. Rivian and Lucid used plate cooling on their EVs. I think that they will have performance issues when performing back to back drag races. Tesla Plaid does not have this issue since they fixed the serpentine ribbon cooling to a parallel ribbon cooling like the Model 3. The optimal design for heat dissipation then would be the tabbed 18650 cell with parallel ribbon cooling based on your analysis. Great job Jordan.
It is interesting that Lucid seems to not have overheating issues despite their bottom cooling design. They started out designing battery packs for EV racing so they must have some other innovation that results in better cooling.
Interesting.
Note that Peter Rawlinson threw side cooling under the bus in favour of Lucid's side cooling. His argument was that it is difficult to get reliable contact with the curved surface area of the battery. I was not convinced.
@@bru512 Peter is right, it is hard to get reliable contact. Tesla bought the company that was making the cooling tubes for them because quality control was not up to the required level. Basically there is a coating on the cooling tube that is cooked on, and it has to be cooked just right. Too "raw" and the surface is slippery and the glue that bonds the cell to the tube slips off. Too "well done" and the coating cracks and peels off the tube. Then the glue used has to be the right mix of the two ingredients, the applicator tube has to be properly maintained and changed often as it will clog over time, etc. One guy who was what they call a CTA (cell tube attach) worker blew off changing the application tips his whole shift, they had to bring finished battery packs back from Fremont and he got fired.
Yeah, just like the "experts" said, the Model 3 battery packs being made on an automated line was impossible, and when they say that just add "for anyone except Tesla" and you may have a true statement.
@@tribalypredisposed How do we know they don't have heating issues?
EV racing only requires packs to last a few cycles.
@@bru512 well, the cars are in the wild now and I don't think there have been reports of acceleration being limited due to heating. I may have missed them, of course.
One thing that may be helping Lucid avoid heating issues is that the pack is enormous at 118 kWh, so the acceleration heats each battery cell less because there are more of them.
With higher amount of cycles for LFP + lower degradation due to better thermal management of the tables design these 4680 batteries will likely outlive other components of the car enabling reuse of battery packs in other cars and/or in future storage packs.
While simultaneously giving more power as the shorter travel path of electrons enables higher current flow increasing the acceleration possibilities and also the charging speed possibilities.
Looking forward to cars being charged at vastly shorter times without degrading them.
Will likely be even more important for Semi & cybertrucks than current passenger models.
Thank you for your very detailed in depth videos! This is braingasm for a chemical engineer 🤩🤓
You'd think! But as Drew Baglino has said, the batteries have already had issues with the cells outliving the pack. Battery packs are a difficult challenge from a durability point of view as well.
@@thelimitingfactor interesting! what part(s) of the packs are failing before the cells? Maybe you have already mentioned this in another video?
Great video as always, appreciate the humility at the beginning further adding to your credibility. Look forward to your next videos!
Great and educational video. Thank you Jordan for your hard work and dedication.
The way that the current collector jumps from the outer edge to the core, skipping the middle layers, is exactly what you would want to reduce the temp increase in the center. If you contacted all the layers then the outer layers would "use up" the cooling potential, make it less cool where it hits the center hotspot. There may be an analogous electrical advantage if the electrical resistance to the center is also higher, though not obvious why that would be so in the tabless design.
Pretty much nailed it. One of the reasons I have a hard time recommending cold plate cooling.
Learning is so great, thanks for bringing us all along on your journey!
Great video. Shows the power of computer simulation ie gut feel is not always right.
I would also have thought Tesla would switch to "bottom/top cooling" since it's far less complex to assemble. The only thing I had my doubts about was the height, because the cells are now even longer, which would make the floor structure difficult for a sedan.
Nice work!
I was just about to go to your channel home page and look for this video when it came up in my feed. "How do they know?"
Thank-you for explaining why ribbon cooling is still better than plate cooling even with the tabbless design. It occurs to me that the thicker can also helps cooling to be more evenly distributed all the way around the cell. Less temperature gradient, fewer hot spots means longer battery life.
Thank-you for responding to my comment that raised this question on another of your videos by recommending this video.
Sure thing man! Yeah, the algorithm is getting smarter than us, lol
I am probably a bit late to mention that if doing base cooling, and there is a thermal runaway event, the expansion has to go down through the base, destroying the cooling at a time when it is needed most
Great video, Jordan! Thoroughly enjoyed learning about battery tech with you as always!
😊
Fantastically informative video. Thank you for making it Jordan.
Sure thing buddy!
I built a LFP battery for a RV that gets used daily - 6yrs old now - new cells were Bottom balanced @2.75 volt -
cell balancer units were not reliable at the time so did not install one - battery discharge to 40% daily - solar charge -
I check battery cell balance every few weeks - cells hover around 4mv difference - Amazingly Good
Thanks Jordan! Vinfast of Vietnam is starting to use an innovative battery pack per Sandy Munro.
🙌🙌🙌😀
Ty for taking the time to so clearly and professionally lay out this presentation. The graphics and production quality hit way above what you'd expect given your subscription count. I know this took a long time e to put together. I learned a lot. I hope your channel grows. Subbed.
Thanks David! Yeah, they're a lot of work, lol.
Thanks again for the great content :) Love your deep dives :)
Great video man. I wonder if this will be the long term or shorter term cooling solution. I would imagine it would continue to evolve as new silicon doping and material changes with v2, v3, etc if they are indeed serious about million mile battery.
Also big congrats on closing in on 100k subs!!
Getting there slowly! lol
Things have kind of levelled off.
Great info. Thanks Jordan.
Professional! Clear! and Well Done!
Thanks a lot for the video and for sharing the reference. You can still use the explanation showed here in order to demonstrate that the prismatic can be as good as a cylindrical 🙂. The conductivity alone is pointless, and using the thermal resistance is more realistic for choosing the best cooling direction ( Thickness/(Conductivity*Cooling_surface). In the case of the cylindrical cell, the radical conductivity is quite poor compared to the height direction. But the radial direction has higher surface. There is a possibility to make the top/bottom cooling better but due to cell integration and important contact resistant in the height (gasket, gaps, electrical insulator) , the height is less interesting. Finally in the case of the LFP from CATL , you can apply the same reasonning and due to the use of the LPF you can have a higher Tmax overall and you do not need higher cooling surface. The sum of improvement of TESLA is driven by cost per performance and tooling is one of them. My guess is that there is less ivestment by staying in cylindrical instead of switching to another form factor. The increase of cell size has been done by CATL and BYD already in 2018 and they have also updated tabs and the number of JR inside the cell in order to cope with the thermal drawbacks
Sure thing! Depends on what your goal is. A full form factor comparison can't be done the comments here. I already point out an upcoming video that Qilin has better thermals than 4680 structural.
@@thelimitingfactor looking forward to it
Class is in session! Let's go Jordan!
I had to keep pausing and rewinding ! There's a ton of info in this video ..
I thought I heard ( but I am not sure from where) that with generation 2 batteries and the new 3 stages combined rolling equipment they were going to omit the copper current collector and laser weld the copper foil turnovers directly to the can base.
Next video
I LOOOOOOVE that kind of content.
Surely this heat management advantage is going to play into improved charging characteristics. Either for one of charging or constant cycling such as the Tesla-Semi is likely to experience.
Another great video, thank you.
I wonder if there's a way to use the natural void in the center of the cell for liquid cooling? This would allow the cells to be closer together creating a higher with volumetric energy density pack. Maybe you could even have a passive mechanical thermostat in the center of each cell, allowing each cell's temperature to be controlled as an individual.
You could, but it would create many other issues with manufacturing, cost, and weight.
The video I've been waiting for!
Excellent rundown.
So now Im thinking that the extreme thickness of the material for the 4680 cans is not just for structural rigidity, but also to increase the thermal conductivity of the cans themselves.
This is one of my favorite channels
🤠
Thank you for battery tech deep dive
I would have also gone for a top/bottom cooling. In a uni e-motorcycle competition i designed the battery pack cooling i such a way, not appreciating the full jellyroll + can approach since the infor the papers showed the later years was one approaching the jellyroll alone, with very poor radial conductivity.
Also, we weren't focused on durability buy max T in 5-10 battery cycles.
For the new prismatic cells bottom heat sink utilization was a no brainer
You get passive baseplate cooling as this up against the pack exterior. The only way to side cool is ribbon.
Nope. Base of pack for venting of liquid in event of thermal overload. Top of pack is via pink goo of death.
Also, cooling between cells maximizes cooling while minimizing cooling lanes required. having coolant flow on the bottom or top of the pack would only cool the cells on one side, and need to be insulated on the other side. (you don`t wanna cool/heat the structure around the cells)
if the cooling channels are not the full height of the pack, they probably won`t hurt rigidity, because the lever is the highest on the top and bottom of the cells anyway. think of hollow structures or half-timbered structures.
Great point!
Regarding weakest cell dictating the pack - having a weak cell is definitely going to have an impact on the entire pack but many BMS systems offer cell balancing - basically taking the energy from the strongest cell and pushing it to the weakest cell (think of it as reaching water level equilibrium at the cell level). I don’t know if Tesla is doing it and even if it does how much energy it can shift from one cell to the other (ie how many amps does the balancing circuit support). In most system cell balancing helps a lot but it’s more of a bandaid and it’s better to try to avoid it by ensuring cells in each pack are balanced and not using outlier cells.
Great presentation as normal
The model 3 LFP pack is already using large format prismatic cells, Munro showed one in one of it videos of him visiting a vendor. I couldn't find any other sources to confirm it, nor did they go into any significant detail like how it was cooled iirc.
Excellent analysis. What you did not say is that one end of the battery is great for cooling, but at the other end there is the electrical connections for both positive and negative. Perhaps also some thin wires which monitor the performance of each cell. So, it will both add complexity and be of less value thermally, perhaps not worth the effort, to extract heat from both ends of the battery in the end cooling scenario.
Thanks!
Cu and AL plates on top and bottom of 4680 are intricate in order to bend each leaf in order to laser weld them to the tab spiral.
Yeah I think I covered that in this video or another one.
Dear Jordan, a small correction: it is not important that the individual cells have almost identical capacity, but that the capacity of sets of parallel cells sums up almost equally. Keep up your excellent work! I did not miss a single episode almost from the beginning.
Hey Martin! Thanks for the insight!
I always assumed that with the tabless 4680s, plate cooling would be the way to go. I was wrong too. I think one phenomenon to emphasize is "thermal contact resistance", especially in a possible next episode about this topic. This is the thermal resistance from very thin layers of a fluid or gas between adjacent solids. For example between the overlapping tabs in the end caps of the cell. This type of resistance can be orders of magnitude larger than the thermal resistance of the adjacent solids. This resistance can really "choke" the overall thermal conductivity in the cell axial direction.
It was always about not *producing* heat, rather than getting rid of excess (imo)
@@rogerstarkey5390 especially around the tab junction to current collectors.
One spot, end of cell, middle of jelly roll, far from cylindrical surface (it’s a spiral, so not half-way).
I’m still getting my head around heat flow ideas.
@@rogerstarkey5390 Yes Tesla for sure has made a huge improvement there.
Yes clearly the correct approach in this case though it's not perhaps the case for other form factors.
Sometimes the initial choice for a particular design maybe the best over time, even for a company which keeps refining its design. The side cooling ribbon design is still bringing the best result for Tesla. However Lucid is doing its cooling through the bottom end of it cells which does not make too much sense in terms of surface contact area!
Do you know of any studies showing which type of batteries are lighting up and what the conditions were? We've seen plenty of fires in line but nothing about which ones, if it was design problems or external. Thanks for your work.
No! I'm curious about that as well though.
Yeah, especially Porsche - specialised cells. Not known to focus on safety! Shouldn’t be when vehicles are idle, parked, on ocean.
🤗THANKS JORDAN AND YOUR PATRONS 👍
GREAT EXPLANATIONS ,EASILY UNDERSTOOD BY LAYPEOPLE…🤔
It would be great to buy you lunch someday,since I am in N.E. OHIO…IF YOU COULD SPARE THE TIME 🤗💚💚💚
Great overview! I hope someone can further clarify the "peak voltage power delivery" aspect of the 4680 vs 2170. Currently a Model 3 loses massive amounts of horsepower as battery SOC gets lower. I assume it's due to rapid voltage sag. Range may be unaffected but a Performance Model 3 with 30% SOC drives nothing like one with 85%. Will the 4680, by it's design, be more able to perform similar to the Tesla Plaid, where the car performs steadily until a much lower SOC is reached?
Lower resistance in the 4680 may help!
Power throttling is a factor of inverter design. Power = Voltage × Current this means you can maintain power even with dropping voltage by increasing current draw and the limiting factor for current draw is the inverter. The tabless design will increase max current with in the cell but I don't think Tesla is drawing max current from the cell.
Awesomeness!
It would seem that the pack encapsulation by the pink material would contribute to heat removal if it is thermally loaded.
I remember when Rivian engineers were making funny remarks about Tesla's ribbon cooling.
I wonder where the Munro and Associates would like to see the breakdown of your battery ideas
Great video Jordan! Does this assume the same coolant inlet temperature?
Thanks! I don't remember the details of the video, it's been a while. I did put the details of the papers on screen so you can find them online. If they're paywalled, use sci-hub.
🤗👍GOOD AFTERNOON JORDAN 👋🤗💚💚💚
Hey man! 🤜🤛
also, the bottom of the cell has a noticeable airgap between the active materials and the casing, thus really not effective cooling area Vs side. Cooling from the top gets challenging as that's where the electrical connections are made for positive and negative welds.
Tesla's battery cells don't really need maximum thermal performance typically. Cells don't get that hot normally unless in extreme conditions like at the track perhaps. Also, uniformity is good when cooling or heating, you don't want the bottom of the cell to be different than the top half, so ribbon cooling cools the entire jacket which then cools the entire cell, making it uniform temperature. Good thermal management is needed for long term performance of the cells, but having maximum thermal conductivity is not even really necessary.
You rock JG
Thanks man 😀
great video as always. could you explain how does the cooling system works in tesla's LFP models? thanks
Good question, I'd actually have to look into that
Wow. Have learned so much watching your videos on your channel. What a humble/open-minded teacher!
I do have a question about the thermals on this 4860 cell. And even the guess that the 4860 cylindrical may be better that that flat rectangular pack (prismatic) for an LFP chemistry package.
You say (at 06:57) that "more surface area per unit of volume, which would improve thermal management" (comparing the CATL prismatic rectangular)
Wouldn't a thin rectangular pack as you display have far greater surface area for a desired VOLUME of battery material? To contain a volume with an outer boundary with the absolute minimum surface area, the sphere is the choice. Next would be the cylinder. Next would be a perfect cube, and rectangular could provide near infinite surface area (really thin).
And beyond surface area, it is unavoidable that the center of the cylindrical cell will be much hotter than the outside than the battery material near the outer radius. If thermal homogeneity is highly desired as you detailed in the video, why would you want to increase the radius of the cylinder, creating even more temperature differential? In fact, would not a thin rectangular pack (as shown from CATL) be a perfect match for a plate cooler with far better thermal bond between package and plate, and minimum thickness of the package?
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Different topic....
In general, I am very confused about this 4680 cell on the thermals. Here is my thinking. Where do I get this wrong?
1) A larger capacity cell will require less number of cells in the final battery pack of a given desired capacity.
2) As cell voltage is same between 2170 and 4860 battery packs, the same number of cells are needed for a series run to 350 volts. Therefore the percent increase in capacity of the bigger cell will necessarily require the same percent reduction of parallel connections of cells.
3) Less parallel runs means that each series run of cells needs to handle more current (for net same pack current in/out). Therefore the percent increase of energy capacity from the smaller cell (2170) to larger cell (4680), WILL ALSO REQUIRE THE SAME PERCENT INCREASE IN CURRENT LOAD CAPABILITY.
4) Assuming volumetric energy densities are maintained between 2170 and 4860 (same chemistry)....
.....for the same net pack current load (between a 2170 cell system and a 4860 cell system), that 4860 battery CELL will have to push 4.45x (volumetric ratio 4860 to 2170) the current of the 2170 CELL. And the losses will be 4.45x the 2170 CELL. That is the heat load to be removed by the cooling system. So far, so good.
5) BUT, in a cylindrical system, for a given length of battery, the ratio of outer surface area to volume is not a constant. As the radius of the battery increases, the volume grows by the square of radius, and the surface area grows only proportional to radius.
In other words, the new 4680 cell has to dissipate 4.45X the losses of the 2170 cell. Simple conductance heat transfer: you better have 4.45x surface area as the 2170 cell to dissipate that higher loss load. But you don't. You have only half of what you should need due to cylindrical surface area/volume ratio that gets lower as radius grows.
That has to be a major challenge.
And now the area of the center of the battery that is generating heat has to travel 2.3x the distance to get to the cooling medium on the outer case. And I would guess that temperature differentials increase 2.3x, further raising the center area temperature.
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I am really confused by this direction. No doubt, less batteries good from a battery production and from a pack construction standpoint. But growing radially versus longitudinally makes absolutely no sense to me.. HELP! Must be doing something wrong on my end.
Glad to hear it! With regards to the thermal management of different cell designs, see my "Pack Analysis" video from a few months ago. You don't always necessarily have to go for maximum cooling. Lots of competing interests.
As for the rest of the questions, I don't have time to answer that many 😁. When I skimmed through it seemed like overall you were on the right track.
@@thelimitingfactor Thx for taking the time to respond, Jordan. I think your comment is the only one to make any sense. The heat load just may not be as big an issue than we think. The average power draw of an EV (or any vehicle) is only about 25% full load power. Full load likely taken at the end of a hard acceleration run. Lots of thermal mass to allow safe intermittent high power operation (if heat was the only concern, as I suspect other issues with high current in the medium).
In any case, keep it coming, man! Great work here!
Bigger batteries with better cooling mean that you can potentially charge every cell on its own, and potentially less cells can be bunched into a group/pack, the ideal being each cell a pack.
It's amazing how many problems around us are related to thermodynamics. The ability to solve them require you to understand the three thermodynamic laws, and in today's world, the ability to computer model your problem using differential equations
Hey, It's all about the Thermodynamics!
Nice to hear that Tesla is focused on making their batteries last.
Still have other components that need the same life cycle (BMS, welds, wiring, moisture intrusion prevention, etc)
Amen!
Minor point, but Its all about "Heat Transfer"
Conduction, Convection, and Radiation,
.......not Thermodynamics
You will not learn about Heat Transfer in a serious textbook/class on Thermodynamics. You would be taking a separate class/textbook for "Heat Transfer."
But you are so right about managing thermals in electrical/electronic/electro-mechanical systems. It is the limit on everything (espec motors/generators).
Jordan does this paper take into account the tabless battery cell?
The paper is linked in the description.
You cannot see which exact cell is defective from a BMS perspective, you can only see that for each voltage set of cells. A faulty cell will drag down voltage of the whole set as they are wired in parallel. It will also limit how much that set can charge. To determine which specific cell in a set is defective, you have to disconnect the cells and test them individually.
Say your battery has 4,416 total cells arranged as 96s46p. If any one of those 96 serial sets of 46 cells in parallel is significantly different than the rest of the battery pack, the entire serial string capacity suffers. This is a disadvantage of small cells (e.g. 18650), as there are so many more of them increasing the likelihood that one will fail compared to 4680s. If an individual cell completely fails with a short - that is actually a better case. The fuse link will blow and you are just out 1/46 of the capacity of the battery as it is taken out of the entire circuit. Same thing if it fails with an open, although in that case no fuse will blow.
I'm trying to square that with the fact that in the examples I've seen, 1 cell has dramatically impacted pack level performance.
@@thelimitingfactor
AKA "The Porsche Problem"?
@@thelimitingfactor Yes, one cell can dramatically impact pack level performance. But you cannot electrically measure the difference between that cell and the rest of the cells in the same voltage set with a BMS. What you can see with the BMS voltage probes is a difference between that set voltage and all the others, as you showed in the video.
Imo, this all ties in with the "odd" charging curve displayed by the "Korean cousins".
They seem to have a "front half,/ rear half" temperature differential which they can't control.
Question: the cells are encased in some tough polymer as the Munro tear down showed. I get that the polymer has limited cooling capacity, unless Tesla designed that material to absorb some heat. Once warmed maybe any potential cooling bennies are negligible?
I note there's construction at Giga Nevada! (Interesting! 😉)
If a pack has faulty cells, can Tesla disable and isolate part of the pack? Could this explain the weight of the Austin Model Y 4680 structural battery pack as per Cleanerwatt's analysis?
No, the Tesla pack would be limited by limiting the voltage range (if it is)
My guess before watching(although I do actually remember them planning on plate cooling) - they found out that the tabless cells produce less heat so they could still use ribbons
I wonder if the cooling becomes less effective towards the rear of the Pack as the heat is absorbed from each cell?
Does this mean the cells towards the rear of the Pack will degrade faster overtime
Or will Tesla reverse the flow of coolant to prevent this from happening
Does this mean the cells in the centre of the Pack will degrade quicker than the ones on the outside of the pack? or are the cooling channels routed differently within the ribbon to compensate for this
No, this is why I said in the video that the gradient isn't as large as you'd expect.
Maybe this is a dumb question, but why packing thausen of cylindrical batteries vertically when you can stretch the battery to 2 meters long pipe like design, and packaging in a horizontal styles, like a floor made of pipes?
That's basically what byd did with the blade, except a ladder frame. Horses for courses.
If it can conduct electricity, it can conduct heat. The current collectors at the top are wicking away heat then conducting over to side can. Dual purpose for sure. The tabless design is also drawing heat out from the center for same reason ohmic resistance is lowered. Did not surprise me that side cooling works.
Can you do an analysis on StoreDot and its battery chemistry?
Any thoughts on Meta Materials battery patents?
Nice job! I think you may have overestimated the thermal conductivity along a thin sheet of electrode and underestimated the thermal conductivity through a thin plastic sheet. It would be interesting to see if the people doin the modelling published numbers for that.
by your logic, shorter fatter cells could cool as well or better than taller cells. But Tesla tends to do full systems analysis and not incremental analysis.
Thanks for all the analysis you do.
Prismatic for LMFP and LFP. It seems that most companies, like CATL's CTP 3.0 Qilian, use prismatic because they can integrate liquid cooling and a thermal heating pad into the pack. It will be much more plug and play with no need for OEM's to engineer complicated thermal management systems, they will just be built in to the battery pack. We should also start to see lithium doped hydroxyapatite added to the separators. Think of a bone material in which the lithium electrolyte flows through. Should be great thermally.and safety wise.