A Little Secret GM Isn’t Telling Us About Improving The Bolt EV Battery

AUG 28 2018 BY GEORGE BOWER 109

What’s one of the biggest complaints about the Chevrolet Bolt EV (besides the seats)?

Slow Charging.

Remember the song “I can’t Drive 55”? It’s about the same thing when it comes to charging speed. Why won’t GM make the Bolt EV charge faster?

Our resident heat transfer expert Keith Ritter made a very interesting discovery when analyzing the Bolt EV battery pack. It was part of a detailed heat transfer investigation of both the Tesla and the Chevrolet Bolt EV batteries.

Keith modeled the heat transfer aspects of the Bolt EV and we discovered that the pinch point for heat transfer out of the cells is the metal “fins” that go between the cell pouches and transfer heat down to the bottom plate. Those metal fins essentially limit the pack charging rate to what it is now.

Here’s another interesting discovery we’ve uncovered in the analysis: If you add another cooling plate ON TOP of the cells you get a factor of 3.5 heat transfer improvement. A factor of 3.5 I asked? It’s got to be a factor of 2. Two plates=twice the heat transfer. Right?

Wrong. There’s a compounding effect. Not only have you added another plate you have cut the effective length of the fin in half, thus the compounding effect.

Now get this. The top of the cells is nice and smooth exactly like the bottom of the cells.

Here are the photos that show that:

Image 1: Bottom of the Bolt’s cells. Photo courtesy John Kelley, Weber University


Image 2: Top of Bolt’s cells.  Photo courtesy John Kelley, Weber University

So the top of the cells are just ready to slap on another plate and we now have enough heat transfer to up the charging rate to 100+kw!

Sounds good to me!

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

Categories: Battery Tech, Chevrolet

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109 Comments on "A Little Secret GM Isn’t Telling Us About Improving The Bolt EV Battery"

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Nix

“the pinch point for heat transfer out of the cells is the metal “fins”

The solution is clear. Bring back the fin. Chevy was 50 years ahead of it’s time and didn’t know they were working on a solution for EV fast charging. 😉

http://blog.classicchevy.com/wp-content/uploads/2014/02/57-Chevy-tail-fin.jpg

dathomir

Made my morning, thx!

Kim Conrad Jorgensen

Who is that “little ray of sunshine” who gave that a “thumbs down”? Come on. Always knew those fins were good for something other than hiding the gas filler cap.

Jean-Pierre White

Awesome idea.

While we are at it we should bring back “Wing Mirrors” which are actually mounted on the wing.

http://www.theminiforum.co.uk/imgreq/img/25d78de1a18b8aecd874250d252a301644ff9d3c/7dc918bd6a0913f374395973561b9de7e93c8759.jpg

Mounting them on the door is lame.

Camera Ready

Yeah, they looked cooler on the wings. But TBH, mounting them anywhere is lame. It’s time for the feds to stop dragging their feet on allowing the automakers to replace side mirrors with aerodynamically superior, tiny cameras.

Bob

I can envision three small screens for the 3 mirrors you’d use now, so no outside mirrors but the same vision on a mirror sized monitor in the placement of your preference.

David Green

Interesting, I had read in Munro’s report on the Bolt that the major issue was the cooling heat exchanger on the other end of the system, Munro had written that it was sized too small to provide optimal cooling. He did not note an issue on the battery pack end.

Counterpoint

Seems to me that if the solution was that simple, Chevy would have already done it. I’m guessing there’s more to it than just adding another cooling plate.

You’re probably right. But the conspiracy theorist inside me says that GM only wants to sell a certain number of these and no more. At least for now. So they don’t want to make the car “too desirable.”

Viking79

It is typical for any product to be sold that way, give it some purposeful limitation so that they can sell you a different one later. I think GM did this with their choice of a small hatchback instead of a more mainstream car. Allows starting at lower volumes. Fast charging could be another. They finally gave the Volt a 7.2 kW charger after many years of requests.

Rafael R Sabatini

Er, unlikely.

Brian

Or a more reasonable theory. CCS chargers didn’t put out more than 50kW until very recently. GM bean counters decided it wasn’t worth the cost to future proof the car build even though the engineering design supported it.

Bill Howland

I think you hit the nail on the head Brian. So what is the little secret GM is not telling us? That battery charging could be easily double what it is? I don’t think easily is the right word. The car does take juice at a 53 kw rate correct? This is possibly the quickest rate that GM can guarantee battery longevity.

Stephen Harris

Think about it–fast charge cell phones don’t get hot. Which means that temperature is simply not the limiting factor in how fast you can charge. In fact, cooling the battery actually makes the battery *more* susceptible to failure from fast charging, since at lower temperature the tendency to plate Li on the graphite electrodes goes up.

Plating of metallic Li on the graphite electrode the is real limitation on how fast you can charge.

Cooling the battery gives a longer life, however, which would lower GM’s cost.

morrisg

Hmm, you say “since at lower temperature the tendency to plate Li on the graphite electrodes goes up” and then you say 2 sentences later “Cooling the battery gives a longer life”. These two statements seem to be in conflict. Can you explain?

Jake Brake

Stephen is right, you have a lower lithium plating limit at lower temps but have to cool the battery to prevent over temperature. By cool I’m talking keep the cells between 45-55’c during a fast charge event. You will actually get better life at these temps then fast charging at 35’C.

Jeff

I think I heard someone say they hit 55 kW on a 100 kW (200A) charging station. Personally I’ve never exceeded 37 kW (at 100A/370V).

The theoretical max should be 40 kW or 80 kW (80%) since the Bolt has a 400V HV system. You won’t get the full output of these charging stations without a 500V system. 55 kW is roughly 68% of the max possible charging rate, which isn’t terrible, although if it can be improved as easily as this article suggests, why not?

Jerry

If the cells can put out 200kw, 200Hp?? in the Bolt, they can easily charge at 150, 125kw whichever it is.
My Volt modules put out 1k amps, 300kw on just 16kwh so LG certainly makes cells that can handle it and with just a 40 mile range, used very hard, deeply discharged a lot.
Yet after 5 yrs they still put out 1k amps a lab tests a bunch every yr of their life.
So this is GMs doing on purpose sabotaging the Bolt from being a viable long distance EV by not doing truly fast charging.

Dan F.

200 HP is about 150 kw. 760 watts = l hp.

Bill Howland

Nope, 746 watts is one horsepower. Europeans use PS = 736 watts, which the english translation of that is ‘Pony Power’.

antrik

Even ignoring peak power vs. sustained power, the maximal charging speed for any given cell type is usually lower than maximal discharge speed.

The cells in the Volt are a different type, optimised for higher power rather than higher capacity.

Rafael R Sabatini

More than likely. Probable. Plus, a lot of these cars do out on leases, so GM was even less motivated to “future proof” a car for standards that are very much in flux yet.

Djoni

Not conspiracy theorie is immune to lazyness and quaterly report.

I bet it’s just that!

GM Bolt need a contender, but so far they had a pass.

Ziv

I have begun to think that GM has intentionally been throttling back demand for all of their plug in vehicles. They have made too many “mistakes” when it comes to marketing and design of their plug in cars for it to be an accident and I don’t think they are that incompetent.

Stephen Harris

No car manufacturer on the planet has made money selling electric vehicles. This is why GM, and all other car makers except Tesla, have “throttled back.” On the other hand, after Tesla, GM has put as many EVs on the road in the US as everyone else combined, apart from Nissan. If you want to blame anyone for “throttling” electric vehicles, why not blame Audi and Mercedes and Lexus? And Volkswagen?

Tesla is a special case. They have made much of their cash flow from selling environmental credits in California to everyone else. Kudos to Tesla. Second kudos to GM and Nissan.

David Green

Stephen, very interesting comment and one of the things I felt will become yet another headwind in Tesla’s future. As more manufacturers sell their own EV’s the value of the ZEV credits drops dramatically. I have previously heard Elon complain about the dropping ZEV value, but at some point, don’t they become almost worthless?

Rafael R Sabatini

Exactly. Tesla have run up $19 Billion in cumulative losses and continue to lose money on every car they build. GM and Nissan are in it to make a profit and will manage prudently, and with a minimum of crazy-drunk-tweeting, to get there.

10 years from now it will be “Dear Tesla, thanks for all the market research your VCs funded. It’s been great! Signed, GM, Nissan, Mercedes, Hyundai and Porsche!”

Todd

Except they actually make money per car, they are just expanding at a ridiculous pace (which I agree needs to be tempered to allow for a more financially sustainable company).

Nix

Rafael, Tesla has also built up $27.91 Billion in Total Assets (source: NASDAQ official listing for TSLA balance sheet, Q218 ibd). So it is inaccurate to look at just spending and pretend that assets are meaningless and don’t count.

It is also wildly inaccurate to divide costs to date for getting the Model 3 into production into just the limited number of units sold as of the end of June (latest month we have financials). That is the same mistake as the folks who said that the Volt cost GM $100K/car to build, when they divided total spending on the Volt program into the first months worth of deliveries.

Foxtrot

Losses are not investment though, so it’s inaccurate to use assets as an excuse for losses. The assets are (nearly) balanced by debt

Spider-Dan

The Volt has the best tech out of any PHEV by far, to the extent that most PHEVs are still behind the Gen1 Volt.
The Bolt has much better tech than any currently available BEV within $10k of its price point.
And you’re saying that those are the results when GM is tanking?

If GM is really that much better at engineering than their competitors, why aren’t they dominating auto sales across the board?

Rafael R Sabatini

please stop with these conspiracy theories. GM is a car company. They are in business to sell cars.

rad

Actually, GM and almost every other company is in business to make money first and foremost. They are achieving that goal by building cars. I give them credit for coming out with a PHEV and a BEV. They are gaining knowledge, experience, patents, etc. Sometime in the future when EV’s become profitable, they will be ready to come out with (and push) more electric vehicles.

Their main concern is (and should be) their stockholders, as they are GM’s owners. As much as I would love them to push EV’s in mass, if I were a stockholder, I would want them to be cautious.

bob

When the fastest growing market is diesel trucks, you have to give them credit for trying to address the EV market too.

theflew

Well part of the reason they might not have done it on the Bolt is cost. If you’re trying to control the price point. Given GM doesn’t state not to charge the car to “100%” daily and in the manual says keep it plugged in when not in use. It appears they are being pretty gentle on the batteries.

Michael

Tesla says to keep the car plugged in when not in use, too. They do recommend not charging to 100%.

Nix

It could be as simple as they had reached the design freeze date on batteries and they had sufficient cooling to pass the desired test parameters, so the continued with what they had done at the time of cutoff. Everyday in manufacturing, managers have to decide when to cut enhancements (and even non-critical bug fixes) off and actually ship. It is adult choice making, where there are not perfect choices.

Enhancing the battery pack cooling beyond the design spec range may have been lower priority than getting the vehicle to market. These are just the hard decisions that have to be made very day by every company. The reality is that the build spec had to be sent off to their supplier by a specified contractual date in order to make a specified deadline.

YVES LAURIN

I agree with you on this, I use to work at Bell Helicopter and I remember engineer where frustrated that they could not solve some problem because the manger said there was no money for it.

One example of that was that on a particular model, they doors where not closing properly and the assemblers had to work a long time to make them fit, but that would not last, the engineer told me that it would take 15 minutes to fix, the manager said no… until a customer said he was returning all his helicopters, they rapidly found some budget

Jerry

The top one is harder than the bottom in many ways.
Personally I don’t understand why they didn’t just use forced cooled, heated air making top and bottom cooling cheap, easy.
But with LG cells if like those in the used Volt modules I sell, just don’t make much heat from such low resistance putting out 16C which I take as about to charge 12C or 6 minutes, from my 40 yr experience SC battery packs. I’ll set mine up for 12 minutes as all the SC will support.
While what he says it true, does it matter?
So I’m not the only one who hated the seats?

Jeff N

I’m not a cooling system expert by any stretch, but I’m inclined to be unconvinced that the existing charging rate limitations are based on battery cooling. When I charged at a 150+ amp charger starting from about 12% it charged at its maximum 150A (~53 kW) for about 20 minutes adding 17 kWh on a warm summer day before the A/C compressor started up to help chill the battery pack.

Maybe this is because the cells are hot but the heat transfer mechanism isn’t capable enough to transfer the heat to the coolant. On the other hand, if the coolant were colder early on by running the A/C sooner then the heat transfer would be more effective due to the temperature differential, right? Yet, they don’t.

Stephen Harris

You are exactly correct.

HVACman
Jeff – Actually, colder glycol to pre-cool a pack is not what you want to do to optimize charge rates. Hot packs charge faster as the internal resistance goes down as cell temperature goes up. The typical DCFC cycle allows the cells to “warm up” first, with zero or very low glycol flow while increasing charging amps as they get warmer until they get close to their design max temperature. Sort of like what the thermostat does in an ICE engine cooling system. Then The TMS hits it heavy with the cooling and coordinates and the BMS regulates amps to hold all cells within +/- about 2 deg. C of each other and not allow any cells exceed the design max temperature. George and I don’t have detailed data on the Bolt’s TMS and BMS control strategy, but we have some good data on the Tesla Model S TMS/BMS charging control strategy based on real-time data collected from Scott F’s CAN bus, which is probably similar conceptually. What we’ve seen is that when the DCFC first starts, the glycol pump remains “off” for a few minutes until the cells warm up to about 40 deg. C (104 F). There is… Read more »
Jeff N

Then why not let the Bolt charge faster than 53 kW at 150A during at least some part of that 20 minutes before the AC kicks on?

Why not charge at 70 kW and kick on the AC after 15 minutes (or whatever)?

Foxtrot

Is the data from Model S TMS online? Would you be willing to share it?

From my experience on high performance prototype EVs, the limits on charge rate are mostly based on avoiding accelerated degradation. The temperature aspect is a little bit of a red herring.

Avoiding the anode potential reaching 0V (wrt to lithium oxidation) is critical. That’s a big motivator to allow temperatures to get up to ~40degC as it speeds up lithium diffusion through SEI layer and into the graphite anode.

If anyone has done degradation tests on a conventional cell (be it LG pouch or 18650/21700), you’ll see that beyond a “critical” C-rate, the degradation gets extreme very quickly. It’s a key difference between the Tesla NCR18650BD cells and NCR18650B or GA. You’ll nuke a B or GA even charging at 1C

Pushmi-Pullyu

Thanks to IEVs for an interesting article, and thanks to IEV readers for an interesting discussion!

Good stuff!

Shaun

I don’t think we can say this definitively until we know more about the battery cells. It’s very possible there are C-rate limitations due to prioritizing cost and energy density, so cooling capacity may not be the limiting factor.

Richard Giddens

Battery thermal management and maximizing battery capacity and longevity / life spans should be of interest to any owner or prospective owner of EV’s. I just saw on YouTube a Tesla Model S 60 owner bemoaning the early death of his battery array that he claims he’s responsible for by abusing the battery with mostly supercharging 100% SOC recharges followed by full discharges. He never used level 2 charging and was always subjecting the battery to 100% charging followed by complete discharging.

Bonaire

It’s a solution that requires thought into “just who are the customers”? What they could/should do is for any car with Combo CCS charger support, add this cooling effect but without that feature, don’t add. A lot of people can get by with 7.2KW L2 at home daily. It’s more likely rare that people really need the 100KW type of charge rates other than: uber/lyft or road-trippers. The Bolt is a small car and I would want something sized larger for real road tripping (luggage, family, dogs, goats, chickens, whatever).

Brian

Why are you bringing your entire farm with you on a road trip? The Bolt is plenty large enough for a family of 4 to road trip in. Throw a cargo box on the roof, and you are good to go. I would know, I took two such trips (over 1000 miles each) within the past month.

Michael

Throw a cargo box on the roof and you’ve killed the aerodynamics of the vehicle, which matters a lot in a long range EV.

Brian

My box gives me about a 15% hit. Running down the highway at 65MPH, I still got 200 miles per charge. It’s a hit, but it’s hardly “killing” the usefulness of the vehicle. Like I said, I took two trips, each over 1,000 miles, both with a roof box, two adults, and two kids.

Warren

Even with just the two of us, we won’t be doing any real road tripping in our Bolt until there is a real CCS DC fast charge network. I’m not holding my breath for that.

ModernMarvelFan

Volt pack design is more far robust but takes up more room/weight.

Bolt design should be sufficient if those cooling fins are made of copper or aluminum. So, it would be the temperature gradient between the cooling fans and the bottom coolant fed plate that determines how much heat is removed (assuming the coolant flowing rate is sufficient and radiator in the front is sufficient).

Warren

The radiator is not used for the battery coolant loop. It is for the motor and power electronics only. GM said the flow from the battery to the reservoir was sufficient except in hot weather when the AC oil cooler chills the coolant.

https://www.gmpartscenter.net/auto-parts/2017/chevrolet/bolt-ev/lt-trim/electric-engine/cooling-system-cat/radiator-and-components-scat

https://www.gmpartscenter.net/oem-parts/gm-oil-cooler-42391604/?c=Zz1jb29saW5nLXN5c3RlbSZzPXJhZGlhdG9yLWFuZC1jb21wb25lbnRzJmk9Q1UxNzA2NTUmcj1sYXllcl8xOCZhPWNoZXZyb2xldCZvPWJvbHQtZXYmeT0yMDE3JnQ9bHQmZT1lbGVjdHJpYw%3D%3D

Bill Howland

Warren really man, you can’t be serious. Both the Volt and the Bolt have a radiator for the electronics loop, and the battery loop. While the electronics loop does not cool the battery – that is true, it doesn’t mean the battery doesn’t have its own cooling system, which it does in both cars. In the Bolt ev, looks to me like the heat from the electronics loop is dumped into the main radiator, as the battery is more sensitive to overheating than the electronics are.

There are 3 separate glycol expansion tanks in each car, the Bolt ev having 1 heating loop, 1 cooling loop, and 1 heating/cooling loop.

Neromanceres

On the road trips we have taken with our Bolt EV we find the charge rate acceptable. The Bolt EV range is sufficient that by the time you need to stop in charge you also need a break and a bite to eat. The charge rate is fast enough that you can sit down have a bite to eat and come back and your ready to go for a few more hours of driving again.

Stephen Harris

Temperature is not the real limit for how fast you can charge–it’s the intrinsic ability of graphite to insert Li ions without plating.

Having said that, a lower temperature will lengthen the life of the battery pack.

Get Real

Lots of reasons for this:
#1 is probably cost, both materials/manufacturing and potential warranty costs–playing it safe and conservative.

#2 is probably GM’s philosophy regarding its EV program. It views EVs as a mainly a hedge for the future while still aggressively making/marketing and selling LICE vehicles especially trucks/SUVs so it doesn’t want push the envelope on DCFC speeds as Tesla and now the Germans are doing as that would begin to erode the main technical advantage of their lucrative LICE sales.

BroncoBet

No, this is never the reasons they compete not just with themselves but with other companies, the number one reason is usually incompetence,as well as they other reasons pointed out above by other posters regarding the process of engineering and costs allotted.
The article was confusing, do they mean that GM will take this step of a cooling cover and improve cooling 2.5 times? That would be a great advance, but when is it slated to become operational? GM did say they would increase production in Q4,they need to increase it at least 100% with improvements like the thermal cooling, as well as the seats. Interesting to see advancements for the Bolt in AV tech as GM is the leader or co leader in that tech.

Cypress

It may mean they will reserve that capability for a higher-end Buick variant.

Foxtrot

Great to see someone with proper electrode knowledge here. Just wrote another comment about how temperature is a red herring and anode surface potential is what’s important.

Are you *the* Stephen Harris?

Also worth mentioning that short periods of higher temperatures during high C-rate operation (charge or discharge) are beneficial for low degradation, it’s time-averaged pack temperature you want to keep low.

Charley

OK…what is the current maximum charging rate? 50 kW?

Brian

55kW

Narg

Neato, charge your Bolt and heat the garage at the same time… I’d rather opt for slow charging while parked at home.

antrik

Slow charging produces about the same amount of heat — just spread out over a longer time.

Bill Howland

Nope. I squared R losses prove that faster charging generates more heat overall. Double the charge rate and you get 4 times the heat. Triple the charge rate and you get 9 times the heat.

antrik

Sure, in linear conductors that’s what happens — but I don’t think that’s how most of the heat losses in electrochemical batteries happen?…

TheCyberKnight

So you’re telling me that the people who designed this whole battery system are not aware of this simple obvious fact?
Sorry, but I doubt it’s a simple as you make it look.

HVACman

No, we are sure GM and LG’s engineers are totally aware of this feature. Engineers do not specify things for no reason. And there are likely very good reasons that they did NOT take advantage of this feature. Cost – weight – added thickness – other factors that limit the charge rate not related to thermal considerations. But it does make us wonder….was there a plan at one time to have higher charge rates and more pack cooling?

Jeffrey Songster

Sounds great how about asking GM if they are aware or intend to do this. The car needs it… Then GM needs to add chargers to the highways. Next… How about more variants of this model … A little electric el Camino based on the Bolt tech… Would sell like hot cakes… Beat Ford and Tesla to the pickup… Come on foot draggers let’s go!

Laura Reinschmidt
I absolutely LOVE my BOLT. I had previously did a 3 year lease of a Nissan Leaf (very disappointed). When that was up leased a Volt. A very nice car, BUT even if I had enough charge, the gas engine turned on in cold driving conditions anyway – hence, I was paying for gas plus the back seat was pretty small. BUT I finally got to test drive a Bolt when they brought them to Kansas City. After one test drive, my husband was also sold. So instead of leasing (which I hated) we bought our Bolt. We have had it for nearly 6 months, and I am still in love with this car! We find the seats are fine – my husband is over 6 feet and weighs about 200 lbs. He finds the seats comfortable too – and my 6’7″ son in law sits comfortably in the back seat! I am extremely happy with this car. The interior is nice – it even has “mood” lighting, which we discovered the first time we drove it at night. After all the hoopla over the Tesla, I think the BOLT is a much better option. I know there are at… Read more »
Michael

Can you describe your use of the car? Since you previously drove a Leaf I presume this serves the same function, local commuter.

antrik

I’m glad that you are happy with the Bolt — but why do you have to bring Tesla into this? These are in an entirely different class.

Brian

Probably because she at least considered the Tesla before deciding that the Bolt was a better option for her. Should we refrain from ever mentioning other makes of EVs, even in passing?

antrik

Without mentioning any reasons for the decision, bringing it up serves no purpose.

The particulars of the chemistry itself in the Bolt EV pack may also be the limiting factor. If the chemistry doesn’t like charging higher than a certain rate, then there would be no need to design the cooling to accommodate higher than the fundamental limits of the chemistry variation chosen.

agzand

As a model gets older, they need to improve the car through its life span. A lot of cars have some shortcomings earlier in their life. They fix them as the model gets older to maintain desirability. At some point GM will improve the charging rates for the Bolt.

DonC

Great and fun article. There might be some other factors at work but you never know. Nice work on the analysis.

HVACman

Thanks:) It is fun to find these little “why’d they do that?” things and then explore the possibilities.

Battery Bill

I^2 * R guys… and as I ramps to meet a constant power target as SOC (and Voltage) decreases, the R also changes due to the effective “c-rate.” Is your thermal expert looking at the big picture on how batteries generate heat under load or oversimplifying? I think you can figure out the answer.

Bill Howland

Yeah agreed.. There is really too much speculation in these articles – I know these guys are retired, but they are zeroing in on the contact point of the battery and seem to be ignoring everything else.

Would help if they had some input from one of the guys who actually designed the thing and HAVE THEM state why they did or did not do something instead of all this total conjecture.

Rennie Allen

Why would’nt GM put the top plate on? It’s obvious to anyone who understands battery chemistry. If you charge at 100kW then you are going to have battery failures earlier, and (unlike Tesla who doesn’t give a crap) GM wants to build vehicles that last a long time.

Tony Williams

Tesla doesn’t “give a crap”? When their ONLY products are battery powered, they more than “give a crap”. They require that their batteri s last (and they do), in addition to being the only auto manufacturer that builds its batteries in house.

Nissan actually sold their battery division. GM buys batteries from South Korea.

HVACman
Good comment and it’s interesting that you referenced the tab cooling paper. I read it a couple of weeks ago. You are correct that uneven cooling and temperature gradients damage cells. But tab cooling hasn’t been applied to any mass-assembled packs I’m familiar with. So optimizing surface cooling is where the industry is right now. And You are correct that GM went to great lengths to ensure even cooling. If you look at John Kelly’s teardown of the Bolt pack, you’ll see the Bolt’s bottom cooling plate uses a two-pass glycol channel that is a marvel of simple design for providing inherently even and balanced cooling to all cells. And a pack with a matching top plate it would still deliver even cooling, just a lot more of it. Regardless of peak cooling capacity, real-time cooling is always modulated via pump speed and AC compressor cycling to maintain proper cell temperatures for maximum allowable amperage. What we’ve seen with numerous packs by GM, Tesla and others that we’ve analyzed is that many of them have are thermally-limited by too-high cell temperature well before the cell internal construction is limited by amps. This is also a factor during peak discharge events,… Read more »
Al D

I’m still waiting for solid-state batteries. There will be no more worries about overheating when they finally arrive. Meanwhile. I’ll just sit on the sidelines while everyone tries to figure out how best to cool these old-tech, liquid electrolyte, Li-ion batteries.

Brian

Way to let the perfect be the enemy of the good.

Al D

I have to say the Bolt is a remarkable feat for GM. It needs a little tweaking here and there and should become a really decent EV in a few years with a lot of orders on the books.

Cypress

Could be they will use that for a higher capacity, higher-end EV based on the Bolt tech.

antrik

First of all, “the Koreans” did *all* the engineering on the Bolt — it was designed at the Korean GM branch (former Daewoo AIUI?), not just the parts that were actually outsourced to LG.

Also, the article actually suggest that GM is well aware of the situation — that’s what the “secret” rhetoric is about… Though frankly, I think it’s rather sensationalist 🙂

antrik

That was a reply to a comment that got deleted. I really wish the comment system wouldn’t cause this kind of confusion… [sigh]

The system is supposed to delete all replies that go with the comment that gets deleted. However, if I’m in the process of deleting the comment while you’re sending the reply, this can happen. Sorry. It’s not perfect.

antrik

Would it be possible to put a placeholder for deleted comments instead?

The system is not able to adapt. It simply deletes the comment and any replies. However, in the strange event that a reply is processing while the moderated comment is getting deleted, there may be a comment here or there that appears on the page but doesn’t show the comment it’s replying to. The system also doesn’t let me know which “other” comments were deleted when I delete the “bad” comment. Only the one that I physically delete goes into the trash. The others just escape into cyberspace (or sadly stay on the page). Fortunately, we are going to a new system when we upgrade our CMS this fall. In the meantime, I’m still playing with settings and moderation features to see what I can achieve.

antrik

Some people already brought this up; but it’s such a fundamental issue that I’d like to further elaborate on it: this article — just as many other discussions on this forum — suggests that cooling is the one key limiting factor to charging speed. That’s just patently wrong. Any particular cell type just can’t be safely charged beyond its design limit, no matter how well you cool it. This depends on chemistry (LFP for example typically has higher C rates than NMC), but also on various design trade-offs that apply even with the same chemistry: such as the thickness of the current collectors (thicker collectors allow more power, but take away from energy density); compression of the the electrode materials (less dense graphite gives more room for fast charging, but less room for storing energy); and the thickness of the active layers (thinner layers allow more power, but less energy). It’s a design trade-off that was most likely decided before even looking into the cooling system.

FarmerDave

Forget Chevy.

LG needs to get right on this problem.
/s

Jim Whitehead

Why didn’t mighty GM realize cooling was a problem with the Bolt battery pack? (The air-cooled Leaf made the same mistake). How can a backyard tinkerer improve Bolt cooling so easily? GM may have some of the best engineering talent in the world, so why didn’t they use them on the Bolt? Elon Musk has said, that the auto giants initially laughed at EVs, so their “A” teams were never worked on them. (The 2019 Jaguar I-Pace is an exception). Will GM learn anything from this article and improve charging? Don’t hold your breath. (I quit working for big companies like GE years ago, frustrated by slow bureaucracy and the “not invented here” syndrome).

bro1999

The Bolt’s BMS does exactly what it’s suppose to do. Cooling is not a “problem with the Bolt battery pack”. It is likely when the engineering team was told “pencils down”, >50 kW and >125A CCS stations weren’t even a thing yet. Despite that, GM engineered the Bolt to charge up to ~55 kW/150A anyways. The only “problem” is the one manufactured in your own mind.

Jake Brake

GM did this design to maximize reliability and reduce potential coolant leaks, not for maximum thermal performance. You barely need a thermal system in a BEV except for fast charge and that’s a lot of cost and complexity to pay for just to save a few minutes on the rare event you decide to fast charge.

Also, GM designs for 99.999% reliability, Tesla designs for 98-99% of customers which is a huge difference in automotive. If you look at everyone’s favorite model s long term battery health chart. It’s a relatively small sample size and even 1 customer with capacity less issues would be unacceptable.

jim stack

Faster Charging means more heat shorter battery life. It also beats up the Power GRID and could lead to Brownouts or blackouts. Better cooling fins may help but is is wasted energy and possible problems. Soon Solid state battery may change that.
The new over 150 kW chargers already need cooled power cords. I don’t think we should keep pushing the limits until we see how they hold up.
The Tesla Super Chargers at 120 kW seem faster than most can eat and get a drink even with poor fast food. I’d even like to slow down the Super Chargers to 60 kW so it cost a little less per minute and doesn’t create as much heat.

antrik

Slowing down the chargers would make them more expensive, since you’d need more of them to serve the same number of users.

James G.

So the improvement will be coming to the next generation Bolt?

GraphiteGuy

George and Keith – as a fellow thermal management geek, I’m interested to know more about how you came to your conclusions. Little things like the conductivity of the fins or the thermal contact impedance between the cell and fin can make a huge difference in the results. Maybe I missed it, but are there more details on your thermal model posted somewhere, or is this just a teaser for future work to be published? Adding a top cold plate may be the “maximum performance” solution, but this approach would add considerable cost and complexity. What about simpler options like increasing the thickness or the thermal conductivity of the fins?