It's the Batteries, Stupid!

[Joseph]

"...any given Tesla battery pack could have lithium cells from more than one supplier... they are all functionally the same. There is really no difference in the product...They do all of the testing on the cells before Tesla receives them. Tesla only takes delivery of cells that meet a certain standard for quality."

From what I've heard (mostly from reading the EVDL) converters, or at least the good ones, try to get batteries from the same production run. This ensures as much conformity between cells as possible.

They may all be 18650 (or whatever) battery size with the same chemistry, but cells from different factories will still be different. After a couple hundred cycles, the weaker and stronger cells will emerge.

As differences arise in each individual cell, it'll get harder and harder for the BMS to balance the pack, which I'm assuming leads to more inefficiency.

I know uneven battery degradation is inevitable, but taking cells from the same production run and manufacturer is a relatively simple step to ensure more reliability and consistency. That in turn keeps battery degradation more in-line.

Maybe Tesla's cell tests (as you say they do) is able to prevent all this. Maybe not.

Considering how paranoid Tesla has been about safety, I'm surprised they aren't employing this relatively simple trick.

[JRP3]

Me too.

[graham]

From this link: AUTOSHOW-INTERVIEW-Tesla may use Evonik battery cell widely | Markets | Reuters over on this thread

Tesla had recently signed a second supply contract with an unidentified Japanese battery cell maker to get dual sourcing on the battery cells, he (Elon Musk) said.

So it sounds like they have at most 2 suppliers. They might not mix the suppliers within the same battery packs...

[TEG]

Tesla had recently signed a second supply contract with an unidentified Japanese battery cell maker to get dual sourcing on the battery cells, he said.

That seems to contradict other recent posts that claim Tesla mixes cells from 6 different manufacturers already.
My gut tells me they want all the same brand of cells in any one ESS box. You want balanced cells and ones from different vendors likely have more variability between them. Perhaps Tesla has identified 6 viable suppliers, but has been buying from one of them so far? I dunno - but "dual sourcing" makes it sound like they have been using one supplier all along which is what I assumed.

[TEG]

By the way, anyone else notice that Evonik sounds like a play on Ovonic?

[doug]

Talking with Rachael back at that 100th Roadster media event, I got the impression that at that point Tesla used only one battery supplier (Japanese), but that the supplier's identity was kept secret.

[TEG]

Yeah, I too had assumed that Tesla loads ESSes with batteries from the same manufacturer (hopefully even the same batch). Mixing cells from 6 different manufacturers sounds like a recipe for disaster, but what do I know?

On the other hand if you convince your one supplier that you are buying from 5 others they are less likely to raise the price!

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And it is only a matter of time before we get some battery breakthroughs pushing things forward. I have to believe that. There is too much R&D and potential for things to stagnate.

At some point EV production could give laptops a "run for the money" in terms of battery sales volume. When that finally happens I suspect Tesla would switchover to a larger format cell so they don't have to put so many of them together.

[TEG]

If it sounds like some of us are repeating the same ideas, it is because postings from multiple topics got merged here. Different people were saying basically the same thing in different places.

[DaveD]

When that finally happens I suspect Tesla would switchover to a larger format cell so they don't have to put so many of them together.

When Siry spoke to a group of Seattle owners at the Roadshow event they had here, he mentioned that they were thinking about the possible future use of larger format Li-ion cells. He even mentioned some format sizes, but I don't recall the (format) numbers he gave.

[malcolm]

They could have different suppliers but the assembly system is set so that cells from the same manufacturer/batch end up in the same vehicle. Would be the only way to reduce variability as much as possible.

If you have six suppliers, you run six battery assembly lines in parallel