Musk & Barra Love Child: Battery “Super Pack” From A TMS Perspective

AUG 31 2018 BY GEORGE BOWER 58

Crazy High C Rates!

It’s a conceptual marriage of the Tesla ribbon-style cooling system and the Chevrolet Bolt EV’s Prismatic-shaped pouch cells. We eliminate the bottom cooling plate.

Once we start cranking up charging rates, pack cooling becomes a big issue. We’re sure that Porsche is learning the hard way since they have promised some pretty high charging rates. Tesla’s Model 3 is the fastest charging EV to date. Model 3 owners are getting 460-480 MPH charging rates right now. With version 3 Superchargers, we are estimating charging rates up to 626 MPH and 157 kW (2 C). The next step is Porsche’s Taycan 800 V charging system, which promises 730 MPH charging (2.4 C).

We’re obsessed with knowing what Porsche will do to get rid of all that heat.

Based on our analysis, they are going to have a tough time doing it with just a bottom cooling plate (see “A little secret GM isn’t telling us about improving the Bolt EV Battery”.

The Bolt EV has a bottom cooling plate design and it is somewhat limited in its cooling and charging ability. Tesla’s cooling ribbon design seems to be about the best there is right now, but how can it be improved?

Enter our new concept in cooling schemes:

A marriage of prismatic cells and Tesla’s cooling ribbon.

At 3C, the Tesla Model 3 could pull down 939 MPH charging rates.

Not too shabby. Sign me up.

*This article was researched and written as a collaboration with Keith Ritter (HVACman)

Categories: Battery Tech, Charging, Chevrolet, Tesla

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58 Comments on "Musk & Barra Love Child: Battery “Super Pack” From A TMS Perspective"

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Bob

I wonder imagine the costs differences between those slim prismatic cells and the Cylindrical cells used by Tesla would be the limiting factor?

mzs112000

AFAIK the Tesla decision to use cylindrical cells originally came down to the fact that they were already mass produced for laptops and other portable electronics. That was able to bring down cost/kWh because economies of scale has already kicked in and delivered low price per cell.
Second was, at the time, cylindrical cells offered higher energy density(AFAIK they still do) than prismatic or pouche cells.

Zach

Also with cylindrical cells you can pack them in unlimited shapes where the prismatic packs are custom per car so again e economies of scale kick in.

SJC

I don’t see the illustration of “economies of scale”.
Where did you get your economics degree?

Dan

The point Zach was trying to make is quite simple – if the same Samsung. cell can support the short eGolf as well as the taller i3, it would be cheaper to mass produce. Today, Samsung makes 2 different cells with different heights for those 2 cars. That being said, the economy of scale there is likely to be pennies if that. The stuff they pack into the two shapes of pouches is the same and the same factory can likely crank out one or the other with a flip of a switch.

morrisg

Not so easy as the flip of a switch. Remember, we’re dealing with fully automated equipment here which means lots of fixturing to hold things accurately while the robot does it’s routine. With a change of form factor you will need a change of fixturing plus calibrating the position of that fixturing to make sure it is in exactly the correct place, plus change of programming for the robots. Not saying it cannot be done, but I am saying it complicates the design of the production line fixtures and programming which increases the costs which must be covered by the price of the cells it builds. Cheaper to do one form factor in higher volume.

antrik

Yeah, the original decision was clearly based on costs, flexibility and density of available off-the-shelf cells.

The more interesting question is why Tesla sticks with this design, now that they have the scale to go with other approaches, if they saw fundamental advantages to them.

Theoretically, all three cell types should offer fairly similar densities, if using the same advanced technology. There are a lot of other design trade-offs at cell and pack level, though — flexibility surely being one of them.

Joel B

Maybe a dumb idea, but wouldn’t it make more sense to pump the glycol into the middle of the pack, and have to flow to either side? That way both sides of the pack will be cooled equally. With pumping it in from only one side, by the time the glycol reaches the far side, it has picked up heat from the first two cells, and will be able to provide limited cooling to the last cell.

Bob

That concept is already in progress: https://chargedevs.com/newswire/xing-mobilitys-electric-supercar-uses-novel-battery-cooling-system/

If not doing the “lego”/modular system like above, I would imagine if someone were to do an entire pack – one of things to consider would be how to ensure all cells have even flow so they are uniform in temperature…

Robert Weekley

Obviously, the fewer cells the coolant passes in the pack, before exiting, the more thermal “Headroom” it has! But also, what say it always has to flow in the same direction? With 2-3 PLC managed valves, flow could be reversed at various thermal intervals, for another!

Joel B

Right – that would make sense. Each cooling channel could run flow in the opposite direction, so each pouch would still be cooled well. Good call.

Null

No valve needed, just reverse pump.

antrik

Typical pumps are not symmetric.

antrik

Both the “lego” concept, and the immersive cooling, are also used by Kreisel Electric.

It’s surely the most effective way to transfer the heat from the cells to the coolant. The downside, I believe, is that all this coolant weighs quite a lot — so it’s probably not the best in terms of gravimetric density.

theflew

Take a look at the Bolt’s cooling plate design. It’s a simple concept, but it’s more complex than just splitting it in half.

Joel B

I had a look at the related article. If I understand it correctly, are they using a basic heat sink to carry heat down to the bottom of the pack, and then pull it away using coolant there? The suggestion there was to put both cooling across the top and bottom of the pack.

It seems like the inevitable trade off between cost/complexity/effectiveness. It might be possible to do per-pouch cooling, but that’s going to require a lot of cooling channels. More parts (so more parts that could possibly fail) and likely a higher production cost. On the other end, you’ve got shared cooling channels (ones that span over multiple pouches), but you trade simplicity for effectiveness.

I also wonder about increasing the flow of the coolant. Increase the flow, and you might be able to get away with an individual cooling channel covering multiple cells.

HVACman

Per-pouch cooling is what the Chevy Volt pack does for cooling. Separate glycol plate for each mirrored pair of cells. A whole lot of plates, all with gaskets, etc. Makes for expensive construction. But great cooling. That is how they can deliver up to 120 kW of power with an 18 kWh battery and keep it cool.

Joel B

I do recall seeing that. And now it does make sense on why the Volt pack has such a high discharge rate. Neat!

ModernMarvelFan

Volt pack is great and expensive. But that is almost out of “necessity” due to its small battery and higher discharge rate. That is the curse of PHEV (that wants to give you a full EV like performance) that requires a high C discharge rate.

Volt’s battery pack has a higher C discharging rate than any of the Tesla packs, especially the Gen 1 Volt pack that has even higher C rate than Gen2.

Null

Oddly you can only charge at 3.6 kWh, now 7.6 kwh in fully optioned Volt. Its almost like GM doesnt want you to use electricity?

Owner gen 2 2016 Volt with just short of 50k miles.

F150 Brian

The real trick will be to use a battery technology that does not generate so much heat, since that is all wasted energy.
I can’t help but think that in a decade, we’ll all be laughing at the packs we have today.

F150 Brian

Or, given the challenges of managing the heat from high current charging and delivery of such high current to chargers, battery swapping may actually be the better solution.
A swap can happen faster that filling an ICE tank (Tesla says 7 minutes, BYD says < 3 minutes)

Jake Brake

NIO is doing it in under 3 minutes and in production today.

Null

Ha! Would you trade your $7,000 pack for one of unknown history?

Only if it was worn out…

Loboc

Use a lease model

eject

Electrolytes of higher conductivity that can be used in thinner layers are key. That is why they all hope for solid state. It could allow separators only a few molecules thick thereby reducing the the conductive path by magnitudes.
We will get there soon.

antrik

The electrolyte is only one element in the equation — and AIUI, it doesn’t actually have heat losses, but rather just limits flow rate?… Other issues are the chemistry itself; electric conduction within the active electrode materials; and the current collectors.

ModernMarvelFan

We already do. there are chemistry such as the ones with LiFe, has much lower heat generation. However, its energy density is about 30% lower.

So, it is a trade off between heat and pack density. Typically, the heat generation correlates with C rate. So, when packs gets larger, for a given output, the C rate naturally drops. That leads to the simpler solution of simply making the packs as large as possible (for a given cost) so it will naturally need less cooling due to lower C rate. The added benefit is longer range and longevity due to lower cycle count for a given mileage.

antrik

First time I hear of LFP having lower heat losses… Do you happen to have some like for that?

antrik

Ergl, I meant to ask for a LINK. Not sure that can be deduced from my garbled post 🙂

eject

The ioniq charges above 2.4C today.

With a small battery and expensive car. It will be interesting to see what the Ioniq will be able to do in the upgraded version to 65 kWh.

Robert Weekley

Most likey High Power Cells, not High Energy Cells! For smaller kWh packs, this is easier!

A123 System Cells could charge at 10C to 15C, but they have a much lower Energy Density!

They could also Safely discharge at up to 30C, continuous! But that means an empty pack in 2 minutes! Suitable then, for Drag Vehicles, like “Killacycle”!

antrik

Indeed. The interesting point here is that the cooling system of the IONIQ — which isn’t particularly outstanding (apparently it’s not even liquid-cooled?) — is able to handle 2.4 C just fine, with the right cell. It just shows that obsessing over ideal heat transfer kinda misses the real issue…

Bryan

wrong topic for this answer.

Please stop with the idiotic “MPH” charging rate. Power and C-rate are the interesting metrics. The US is already fact- and science impaired, please stop adding to it.

When planning trips, some people really appreciate knowing how many miles they’ll be able to add in an hour. It’s super simple and straightforward. For the average person, taking an EV on a road trip and planning stops, meals, etc., this metric can be very welcome. Talk about power and C-rate with a newbie that is considering an EV and wants some easy-to-understand data about traveling in an EV, you may lose them pretty quick.

Calling it idiotic is a bit harsh.

ModernMarvelFan

But using “MPH” as charging rate is mislead because people will start to compare. That MPH rating is highly impacted by efficiency of using the energy, not just charging the battery. So, it can leads to false conclusions…

We don’t use “MPH” refilling rate for gas tanks.

Then again, people do use the stupid metric of “miles per tank”…

antrik

The fact that “mph” charging rates takes efficiency into account is actually its big strength.

Admittedly, it’s probably not the best metric when comparing cooling system efficiencies…

Null

But it is what functionaly matters.

Bryan

I agree when I am comparing how two cars compare for charge rates I compare the whole package. That includes vehicle efficiency, battery cooling and BOS.

If I am comparing just a battery I look at C rating as that is the only parameter to be considered.

BTW, I work in the stationary storage part of the PV industry with a 5.5 kW hybrid inverter and multiple LFP and LNMC batteries.

Leptoquark

Great headline!

Thom Moore

Thanks for the most intelligent and well informed article on this subject to date!

anon

Congratulations! You just invented the Volt cooling system circa 2011. Does everything here have to have a basis in Tesla?

theflew

Agreed. The Volt has a very complex efficient cooling system. It also takes a lot more room than the Bolts design.

HVACman

Agreed that conceptually, it is similar to the Volt. But it also is entirely different, with this variation essentially identical to the Tesla cooling snack pack cooling solution that is relatively easy to build, especially with flat pouch cells. The Volt’s pack is very complex to assemble, especially with the cooling plate configuration. Each plate has 4 o-rings to seal off at the external manifold. x 192 cells, that is a lot of potential leak-points.

George did a great comparison article on the Tesla ribbon system vs the Volt system a few years ago. Link below:

https://insideevs.com/tesla-or-gm-who-has-the-best-battery-thermal-management-bower/

Neromanceres

I don’t agree with premise. The issue with the ribbon cooling system is that it’s a series system that will lead to uneven cooling-heating of the pack. It’s why GM rejected such a design. Technically the best design would be something like what is in the Volt. Where the coolant is a parallel flow design with the coolant running directly through the fins separating the cell groups.

That being said it’s likely that GM set the charge rate first (to meet their degradation spec) and designed a cost effective cooling system that could accommodate that. Not the other way around.

antrik

Almost all cooling systems on the market have at least part of the cells in “series” — so the temperature difference can’t be that much of a problem. And if it *really* was, just reversing the direction of the coolant flow regularly would allow for a perfectly even distribution. The fact that nobody bothers doing it like that, is further confirmation that it doesn’t really matter.

Part of the reason it doesn’t matter is that temperature gradients *inside* each cell actually tend to be much larger.

Null

Thermal density and flow rate matters.

alohart

Are these comparisons of Porsche’s 800 V charging system with today’s 400 V systems taking into account that 800 V charging has twice the charging power of 400 V charging at the same current, or that 1C charging at 800 V requires half the current of 1C charging at 400 V and thus generates half the waste heat? At the same charging current, a Porsche Taycan could charge twice as fast as a 400 V charging system with the same amount of waste heat. So I’m mystified why “we’re obsessed with knowing what Porsche will do to get rid of all that heat.”

antrik

Higher pack voltage does *not* result in significantly less waste heat. The individual cells still work at exactly the same voltages and currents. The only thing that benefits are the bus bars, which can carry the same amount of power with a lower cross-section.

(Heat losses in the bus bars are theoretically affected — but these losses are actually insignificant compared to those inside the cells.)

antrik

I wish these articles were less sensationalist. It’s surely fun to play with the numbers — but it’s not like you came up with some breakthrough idea here… The downside of this concept is a lot of extra weight and wasted space, which is most likely not a good trade-off. If you value maximal heat transfer over weight savings, immersed cells are clearly the most effective approach.

And frankly, while you clearly know a lot about heat transfer in general, I don’t get the impression that you understand batteries all that well. The major problem with pouch cells is not heat transfer away from the cells, but heat transfer from layer to layer *within* the cells. That’s why tab cooling is so much more effective than surface cooling: the heat doesn’t have to pass between the layers.

(One major advantage of cylindrical cells AIUI is that the negative electrode is attached directly to the can — so cooling the can is in fact a form of tab cooling, not just surface cooling!)

Kdawg

Why did the Hipster get such a terrible charging rate?
Because he plugged in his EV *before* it was cool.

morrisg

Hi George: a quick question. Since Tesla battery systems are nominal 400v and the Porsche battery system is 800v, even at the same charge current doesn’t the Porsche battery system take on power at twice the Tesla’s rate? Same current, but twice as many cells in the series stack so twice the amount of power per unit time. Thanks for your engineering based articles!

antrik

Pack voltage doesn’t affect the C-rate of the individual cells, and thus cooling requirements.

Bill Howland

Why you guys obsess over this is beyond me. I didn’t know the point of failure in the car was an overheating battery pack, not in GM cars anyway.

Null

Bolts quick charge rate drops rapidly because they cant get heat out fast enough. Second quick charge is still hot from first so starts out impaired.

antrik

I don’t see how a second quick charge can be affected by a previous charge, with hours of driving in between… Unless the battery had no active cooling at all.