Rivian's hot lunch

liveforphysics · Jun 14, 2022

I would not use epoxy, it tends to crack when cold and experiences thermal expansion-contraction stresses.

You want something that won't be experiencing a phase change inside the normal operating temp range, and won't get brittle when cold.

You want something with elastomeric or viscoelastic compliance.

I like the urethanes and urathane-urea hybrids. I like them to be filled with the right endothermic fillers so it also rapidly clamps thermal runaway propagation in the event a cell defect or mfg defect or user damage.

john61ct · Jun 14, 2022

Any links or other specifics for us?

liveforphysics said:
I would not use epoxy, it tends to crack when cold and experiences thermal expansion-contraction stresses.

You want something that won't be experiencing a phase change inside the normal operating temp range, and won't get brittle when cold.

You want something with elastomeric or viscoelastic compliance.

I like the urethanes and urathane-urea hybrids. I like them to be filled with the right endothermic fillers so it also rapidly clamps thermal runaway propagation in the event a cell defect or mfg defect or user damage.

liveforphysics · Jun 15, 2022

I've had good luck with many of this company's products.

https://www.epicresins.com/ElectronicsPotting

I'm not going to call out a specific compound, because different cells and pack designs do better with different compound attributes. For example, pouches need more viscoelastic behavior than cylinders, and sometimes thermal conductivity is wanted or not wanted.

Toorbough ULL-Zeveigh · Jun 15, 2022

cuppola questions for the battery jockey...

why not make a battery that is both potted & modular (maybe already do to certain extent), rather than one huge monolith so it could still be repaired?
in that case six is a perfect number for example the number of cells in toyota nimh modules.
so extending that idea to the max, then pot individual cells. :banana:

also how much of a hit in the density parametrics does potting eat into; 50%?

liveforphysics · Jun 15, 2022

Many folks go that route of assembling potted modules into a larger pack assembly.

It's certainly better than unpotted, but each additional electrical connection point per module ends up adding connector cost and failure mode locations for corrosion vulnerability.

There are many ways to accomplish the goal of making a battery pack, the trick is in picking the one that best suits your objectives.

liveforphysics · Jun 16, 2022

Toorbough ULL-Zeveigh said:
also how much of a hit in the density parametrics does potting eat into; 50%?

It depends on if the design is optimized for potting. As little as -6% pack grammatic impact. As much as 20-35%.

JackFlorey · Jun 16, 2022

Toorbough ULL-Zeveigh said:
why not make a battery that is both potted & modular (maybe already do to certain extent), rather than one huge monolith so it could still be repaired?

It's all a tradeoff. State of the art in li-ion is changing rapidly now, and it's very likely that in 10 years no one will make the cells you need to fix a battery. So if you pot it and that makes it reliable enough that you don't _need_ to fix it in 10 years? That might be an overall win for car owners.

Hillhater · Jun 16, 2022

JackFlorey said:
Toorbough ULL-Zeveigh said:

why not make a battery that is both potted & modular (maybe already do to certain extent), rather than one huge monolith so it could still be repaired?

Click to expand...

It's all a tradeoff. State of the art in li-ion is changing rapidly now, and it's very likely that in 10 years no one will make the cells you need to fix a battery. So if you pot it and that makes it reliable enough that you don't _need_ to fix it in 10 years? That might be an overall win for car owners.

Not an attractive image Jack.
If in 10 yrs that expensive pack is not repairable,.. and hence likely not useable for other purposes either ,..then the only option would be recycling ...but what if battery tech/ chemistry has moved on such that those materials are no longer economic to recycle ?
In the meantime, that 10 yr old EV has to be adapted to a new battery tech to be of any future use
...At what costs ?

JackFlorey · Jun 16, 2022

Hillhater said:
If in 10 yrs that expensive pack is not repairable,.. and hence likely not useable for other purposes either ,..then the only option would be recycling .

Or second life use.

but what if battery tech/ chemistry has moved on such that those materials are no longer economic to recycle ?

Then we won't need the materials any more. Good for us. We've solved our problem.

In the meantime, that 10 yr old EV has to be adapted to a new battery tech to be of any future use

If the new batteries are now better/cheaper/easier to source - why on earth wouldn't he get a new battery?

Hillhater · Jun 20, 2022

JackFlorey said:
Hillhater said:

If in 10 yrs that expensive pack is not repairable,.. and hence likely not useable for other purposes either ,..then the only option would be recycling .

Click to expand...

Or second life use.

Read the comment jack !....it is damaged, not just reduced capacity, ..possibly dead /swollen/leaking, cells.
Dangerous to reuse .

JackFlorey said:
but what if battery tech/ chemistry has moved on such that those materials are no longer economic to recycle ?

Click to expand...

Then we won't need the materials any more. Good for us. We've solved our problem..

Have we ? ..if they are not economical to recycle, then how will they be disposed of ?.....Landfill ?

JackFlorey said:
In the meantime, that 10 yr old EV has to be adapted to a new battery tech to be of any future use

Click to expand...

If the new batteries are now better/cheaper/easier to source - why on earth wouldn't he get a new battery?

.. may be because because the older tech EV may well need a lot of mods to fit and function correctly or legally with a new battery system adapted. Plus the cost of the whole new pack may well make the conversion financially not worthwhile for a 10 yr old car.
A bit like trying to update those early Honda insights, and NmHi Prius’s with Lipo or LfePo4 packs
...or update an early model3 Tesla, with the new 4680 or CATL cell packs ?
.. IE, uneconomical conversion, so more “short life” waste to recycle.

JackFlorey · Jun 20, 2022

Hillhater said:
Read the comment jack !....it is damaged, not just reduced capacity, ..possibly dead /swollen/leaking, cells.
Dangerous to reuse .

Yep. Some packs will be like that. The vast, vast majority will simply be old - installed in a car that was junked for other reasons, or replaced because the range has dropped.

Have we ? ..if they are not economical to recycle, then how will they be disposed of ?.....Landfill ?

.. may be because because the older tech EV may well need a lot of mods to fit and function correctly or legally with a new battery system adapted.

Perhaps!

Yoy envision a scenario where smart/skilled people know how to replace individual cells and rebalance the battery. If those smart/skilled people exist, they will likely be able to perform those mods.

A bit like trying to update those early Honda insights, and NmHi Prius’s with Lipo or LfePo4 packs

Indeed. I've considered doing this myself. However, it's a lot more work than just replacing a battery.

https://www.youtube.com/watch?v=2ih8Ff5EtK8

Hillhater · Jun 21, 2022

JackFlorey said:
Yep. Some packs will be like that. The vast, vast majority will simply be old - installed in a car that was junked for other reasons, or replaced because the range has dropped.

you are not following the point jack !.. we are talking of potted packs with DEFECTIVE CELLS.!

JackFlorey said:
Yoy envision a scenario where smart/skilled people know how to replace individual cells and rebalance the battery. If those smart/skilled people exist, they will likely be able to perform those mods....

Sure, but at what cost ?( this is a 10 yr old car remember !)

JackFlorey said:
A bit like trying to update those early Honda insights, and NmHi Prius’s with Lipo or LfePo4 packs

Click to expand...

Indeed. I've considered doing this myself. However, it's a lot more work than just replacing a battery.

My point exactly !
[/quote]

spinningmagnets · Jun 21, 2022

I'm now wondering about potting just the P-groups..

If one cell goes bad, it will drain down the rest of the P-group, so its not throwing away good cells too, they are toast anyways.

JackFlorey · Jun 21, 2022

Hillhater said:
you are not following the point jack !.. we are talking of potted packs with DEFECTIVE CELLS.!

Nope. Please keep up. Chalo's concern was that potting "will result in car packs going to landfill early." Solutions include repair AND reuse.

Sure, but at what cost ?( this is a 10 yr old car remember !)

If all they need is a CAN bus translator, very cheap. If they need a whole new battery frame, very expensive.

JackFlorey · Jun 21, 2022

spinningmagnets said:
If one cell goes bad, it will drain down the rest of the P-group, so its not throwing away good cells too, they are toast anyways.

Yep. The cases where you can replace one cell and have a working pack again are very few and far between.

Tesla? No way.
Leaf? Maybe - but only if the cell hasn't started burning. And you can't replace a single cell anyway.
Ultium? Again, no way. But you can replace the module.

liveforphysics · Jun 21, 2022

spinningmagnets said:
I'm now wondering about potting just the P-groups..

If one cell goes bad, it will drain down the rest of the P-group, so its not throwing away good cells too, they are toast anyways.

Potting each cell group would be a great improvement over no potting. It would still leave the need to corrosion proof your series connections afterwards, but might be a good middle ground for a DIY'er if you're a skilled maker.

For OEM products, I personally like them to be solid potting enveloping the cells of a type which halts propagation. The chances of getting a defective cell is similar to your odds of lightning strike using today's modern cell QC processes.

Hillhater · Jun 21, 2022

liveforphysics said:
...... The chances of getting a defective cell is similar to your odds of lightning strike using today's modern cell QC processes.

..?? Such a LGs QC proceedures ??

Hillhater · Jun 21, 2022

JackFlorey said:
........ Chalo's concern was that potting "will result in car packs going to landfill early." Solutions include repair AND reuse.

Thats just YOUR interpretation .....
Maybe you didnt read the part about ......

Chalo said:
.....In an industry that's fully accustomed to rebuilds, core swaps, pick and pull, etc., I don't think it's a good thing to take the single most expensive component in an expensive car and make it disposable.

JackFlorey · Jun 21, 2022

liveforphysics said:
Potting each cell group would be a great improvement over no potting.

And if the potting included a relief to (safely) vent the cell, and phase change material sufficient to absorb the heat of combustion to prevent fault propagation - you could drastically reduce the odds of battery fires.

At least two manufacturers make such a material; they machine it into cell sleeves and cell array holders. I don't know of anyone who makes it as a potting material though.

liveforphysics · Jun 21, 2022

You're thinking of a phase change wax material that resets when it cools down. They have just enough energy absorbing to moderate normal operating cell temps.

What I'm talking about us a temperature actived chemical decomposition which is strongly endothermic, and what it takes to stop the hundreds of kW thermal power pulse when the cell goes into runaway.

The wax phase change energy values just don't come even close to working on paper to stop thermal runaway. The single time chemical bond cracking of the solids in the potting is over 100x more energy absorbing for its size and mass.

The endothermic solid fillers are blended into the potting with as high of loading as possible, which enables thermal runaway stopping power with the smallest system mass and weight due to tightest cell spacing.

spinningmagnets · Jun 22, 2022

I now have one more reason to like 14S. In my new theoretical pack, (5P?), the P-groups are potted and a year down the road one P-group goes bad (*one in a million).

If I remove the bad P-group (easily found with DMM), I still have 13S available to run my coffee pot after a storm and temporary power outage.

Using my nominal 48V inverter.

CONSIDERABLE SHOUTING · Jun 22, 2022

spinningmagnets said:
I'm now wondering about potting just the P-groups..

If one cell goes bad, it will drain down the rest of the P-group, so its not throwing away good cells too, they are toast anyways.

We're also not talking about handmade eBike packs from salvaged Dyson battery packs; we're talking OEM electric-car qualities here. Top shelf kind of stuff! Batteries that are used over a decade in packs lasting 600,000+ miles. But the time cells begin to die, you're pack is likely so old you have other concerns- and jacking a new cell in is going to give you all the same problems of a brand new cell in a used, high internal resistance pack.

JackFlorey · Jun 22, 2022

liveforphysics said:
The wax phase change energy values just don't come even close to working on paper to stop thermal runaway. The single time chemical bond cracking of the solids in the potting is over 100x more energy absorbing for its size and mass.

This wasn't wax. It was a rigid material machined into shapes to hold cells. The wall thickness was controlled to ensure that it could absorb the energy of a single cell lighting off while protecting the cells around it. Didn't see it in action, but they had several videos of the material protecting the cells around a burning cell. This was from SPI/ESI 2019.

liveforphysics · Jun 22, 2022

JackFlorey said:
liveforphysics said:

The wax phase change energy values just don't come even close to working on paper to stop thermal runaway. The single time chemical bond cracking of the solids in the potting is over 100x more energy absorbing for its size and mass.

Click to expand...

This wasn't wax. It was a rigid material machined into shapes to hold cells. The wall thickness was controlled to ensure that it could absorb the energy of a single cell lighting off while protecting the cells around it. Didn't see it in action, but they had several videos of the material protecting the cells around a burning cell. This was from SPI/ESI 2019.

It sounds like you're still describing a wax phase change product. Companies like all-cell use a carbon foam that's saturated in parafins, and machine it into cell holders.
Phase changes just don't have the thermal energy quenching density to stop runaway at useful cell spacing sadly.

There's always a test condition you can create where with no potting it passes PPR, and companies marketing stuff figure this out to help them make padded product demos. Keep decreasing SOC% and increasing cell to cell spacing, and eventually any product looks great.

The magic is in getting the tightest passing cell spacing, running multi-initation PPR at 100% SOC and preheated to 60degC. This takes real thermal quenching power.

Also, beware, some of the machined carbon wax block materials are weakly elecrically conductive, this means they rely on shrink and insulators to not slowly self discharge.

Chalo · Jun 26, 2022

https://www.businessinsider.com/tesla-is-sacking-staff-who-recently-started-withdrawing-job-offers-2022-6

Rivian isn't the only EV outfit tasting one of the drawbacks of basing your company on a Ponzi scheme.

Rivian's hot lunch

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