[sliken]

From an engineering perspective it's suboptimal since they have small surface area relative to volume. That's probably why Telsa went with the 2170 instead of the 26650, which has a larger diameter.

Despite this disadvantage the Telsa battery cost, power density, cost per kwh, peak power, and longevity are unmatched. Especially as measure by real people driving real cars on real roads.

So sure in theory batteries with more surface area would have greater package efficiencies. So far nobody has managed to.

[akira2501]

> So sure in theory batteries with more surface area would have greater package efficiencies.

There's way more to a battery than just density; however, one of the things that needs to be managed is the heat generated during charging. There might be a case to be made for slightly suboptimal packaging strategies if it makes cooling all those cells that much easier.

[rconti]

Yeah, this really strikes me as a forest for the trees kind of situation. Sometimes it pays to engineer things to death, other times you need to step back and see the whole picture; how important is packaging for efficiency vs cooling vs manufacturing speed, etc.

Automakers putting battery packs in the trunk of their cars are complaining about battery size.

Is anyone complaining the floor on a Tesla is too thick and compromises interior space? Of course not.

The packaging probably DOES add a not-insignificant amount to the total weight of the pack vs an ideal battery of some custom design. But again, you have to weigh (ha!) all of the factors.

[Gibbon1]

I read an article that made the case that lithium of batteries are sensitive to the direction of the heat gradient. Tried looking, can't find it. But the upshot was you want the gradient parallel to the electrode layers not perpendicular. Which means you want to remove the heat from the ends of the cell.

[ecpottinger]

I can't find it either, but I remember reading it.

However, http://jes.ecsdl.org/content/163/9/A1846.full points out some of the details.

[Gibbon1]

That actually I think is what I was looking for.

Money quote: For automotive applications where 80% capacity is considered end-of-life, using tab cooling rather than surface cooling would therefore be equivalent to extending the lifetime of a pack by 3 times, or reducing the lifetime cost by 66%.

Meaning battery packs that last not 150,000 miles, but 450,000 miles.

[mavhc]

Don't most other EVs use flat pouch cell batteries?

[greglindahl]

I think GM switched from pouch cells to cylindrical cells between the Volt and Bolt. The Leaf still uses a flat pouch. In the US, the Bolt and Leaf are the only other BEVs with significant sales.