5 ms·

This cylindrical form factor might make sense for batteries that have thermal runaway potential, to keep the unit size small so that the whole battery doesn't g

This cylindrical form factor might make sense for batteries that have thermal runaway potential, to keep the unit size small so that the whole battery doesn't go into thermal runaway, only one cell. But for LFP or iron based batteries which don't have such issues, the blade design should be cheaper, more maintainable, more space and weight efficient etc. There's no glue so you can actually just switch individual blades. Cooling channels can be straight.

colejohnson66 5y ago
Assuming this image I found online is of 4680s, there’s quite a bit of wasted space: https://www.teslarati.com/wp-content/uploads/2021/01/tesla-4680-battery-cells.jpg https://www.teslarati.com/wp-content/uploads/2021/01/tesla-4...
- dahfizz 5y ago
  Volumetric efficiency is not a big concern for EVs. They already have more storage than an equivalent ICE vehicle (frunk, no trans tunnel, etc). Giving up space for better weight and cooling is worth it.
- meragrin_ 5y ago
  Isn't some of that "wasted" space necessary for cooling the batteries?
- trainsarebetter 5y ago
  offset every row and significant reduction in “wasted space” also cooling is a huge part of what makes these work. We have to stop looking at battery’s from purely a cell level. Add in the structural element, and the claim is they are now more volumetric and weight efficient than traditional packs.
- Goz3rr 5y ago
  The actual arrangement of cylindrical cells is staggered: https://cdn.motor1.com/images/mgl/XkV66/s1/tesla-model-y-4680-type-cylindrical-cells-and-structural-battery-source-paul-kelly.jpg https://cdn.motor1.com/images/mgl/XkV66/s1/tesla-model-y-468...
  - Gravityloss 5y ago
    Exactly. Sandy Munro has an excellent video with multiple different battery packs torn down and compared: https://www.youtube.com/watch?v=4JiDZVO9NdM https://www.youtube.com/watch?v=4JiDZVO9NdM You can see that the cooling channels in the Tesla pack are these hollow undulating aluminum shapes. Can imagine they're not very cheap. Also the Tesla packs are filled with some kind of bonding foam, making repairs near impossible.
    - Tempest1981 5y ago
      > bonding foam Is that maybe to reduce the spread of fire? I know Tesla put a lot of work into that. Others too, I hope.
  - cma 5y ago
    Why not use two size tiers of cylindrical cells, smaller ones to fill in the gaps? With only one size the empty space ratio is the same.
    - Armisael16 5y ago
      It definitely isn’t the same. The square packing in the first picture uses pi/4 ~ 79% of the space; the second uses pi/(2*sqrt(3)) ~ 91% of the space. They don’t bother with smaller secondary batteries because the extra manufacturing cost and operational complexity isn’t worth it for a 5%-10% bump in volumetric energy density.
      - cma 5y ago
        I didn't mean to say the two packings were the same. 90% is better than I thought circle packing was though, I've mostly seen multi-scale packing used in thermal pastes and stuff and it is probably a bigger difference in 3d sphere packing.
      - hinkley 5y ago
        Didn’t someone prove about 15 years ago that there’s an oval shape that packs tighter still? Given the hollow core that could probably be done, but cylinders are probably easier for the assembly line to handle. So then it comes down to whether that space is being utilized (for cooling, or weight per cubic inch of the support structure).
kube-system 5y ago
Sounds like the form factor Toyota has used in their NiMH packs for basically forever. They’re surprisingly serviceable for DIYers.
- mrfusion 5y ago
  So Toyota still uses nimh in its hybrids? Does that make them longer lasting?
  - kube-system 5y ago
    They currently use some of both NiMh and Li-ion. Toyota is notoriously conservative when choosing technologies. My guess is they still use a lot of NiMH because they have proven long-term reliability, more forgiving characteristics in harsh use, and they already have a lot of existing tooling to support them. If there any single car that has made the general public comfortable with very expensive batteries in their car: it’s the Prius.
    - ButchC 5y ago
      All those things are true when comparing NiMH to NiCd but definitely not compared to lithium batteries. There's not a single metric for which you can't find a superior suitable lithium chemistry. Except for one: $Cost Just Toyota doing Toyota things. Also I would strongly disagree on the Prius comment. A lot of "HV battery fault" cars out there back in the day, refurbing them was a pretty good business for a while. The NiMH pack in the Prius was the basis for so many slack jawed comments "EVs will never work! You're just going to have to replace the battery every 5 years!"
      - kube-system 5y ago
        Cost, as you mentioned, is one reason. However they also fare better at extended temperature ranges and under long periods of self discharge. They are, generally speaking, more forgiving of a battery chemistry. Your quote about rollout of the Prius is exactly my point. That opinion was widespread when the Prius was introduced. The reliability of the Prius since then has changed public opinion greatly.
vardump 5y ago
Isn't cylindrical form factor simply easier and cheaper to manufacture? Decades of industry experience manufacturing a ton of cylindrical products.
stetrain 5y ago
My understanding is Tesla currently uses cylindrical cells for NCA packs and blade/prismatic cells for LFP battery packs.
konspence 5y ago
How would a cylindrical shape isolate thermal runaway to one cell?
- snovv_crash 5y ago
  During fire they vent from one end, not in the middle. So this directs any flames away from adjacent cells.

colejohnson66 5y ago

Assuming this image I found online is of 4680s, there’s quite a bit of wasted space: https://www.teslarati.com/wp-content/uploads/2021/01/tesla-4680-battery-cells.jpg https://www.teslarati.com/wp-content/uploads/2021/01/tesla-4...

dahfizz 5y ago
Volumetric efficiency is not a big concern for EVs. They already have more storage than an equivalent ICE vehicle (frunk, no trans tunnel, etc). Giving up space for better weight and cooling is worth it.
meragrin_ 5y ago
Isn't some of that "wasted" space necessary for cooling the batteries?
trainsarebetter 5y ago
offset every row and significant reduction in “wasted space” also cooling is a huge part of what makes these work. We have to stop looking at battery’s from purely a cell level. Add in the structural element, and the claim is they are now more volumetric and weight efficient than traditional packs.
Goz3rr 5y ago
The actual arrangement of cylindrical cells is staggered: https://cdn.motor1.com/images/mgl/XkV66/s1/tesla-model-y-4680-type-cylindrical-cells-and-structural-battery-source-paul-kelly.jpg https://cdn.motor1.com/images/mgl/XkV66/s1/tesla-model-y-468...
- Gravityloss 5y ago
  Exactly. Sandy Munro has an excellent video with multiple different battery packs torn down and compared: https://www.youtube.com/watch?v=4JiDZVO9NdM https://www.youtube.com/watch?v=4JiDZVO9NdM You can see that the cooling channels in the Tesla pack are these hollow undulating aluminum shapes. Can imagine they're not very cheap. Also the Tesla packs are filled with some kind of bonding foam, making repairs near impossible.
  - Tempest1981 5y ago
    > bonding foam Is that maybe to reduce the spread of fire? I know Tesla put a lot of work into that. Others too, I hope.
- cma 5y ago
  Why not use two size tiers of cylindrical cells, smaller ones to fill in the gaps? With only one size the empty space ratio is the same.
  - Armisael16 5y ago
    It definitely isn’t the same. The square packing in the first picture uses pi/4 ~ 79% of the space; the second uses pi/(2*sqrt(3)) ~ 91% of the space. They don’t bother with smaller secondary batteries because the extra manufacturing cost and operational complexity isn’t worth it for a 5%-10% bump in volumetric energy density.
    - cma 5y ago
      I didn't mean to say the two packings were the same. 90% is better than I thought circle packing was though, I've mostly seen multi-scale packing used in thermal pastes and stuff and it is probably a bigger difference in 3d sphere packing.
    - hinkley 5y ago
      Didn’t someone prove about 15 years ago that there’s an oval shape that packs tighter still? Given the hollow core that could probably be done, but cylinders are probably easier for the assembly line to handle. So then it comes down to whether that space is being utilized (for cooling, or weight per cubic inch of the support structure).

kube-system 5y ago

Sounds like the form factor Toyota has used in their NiMH packs for basically forever. They’re surprisingly serviceable for DIYers.

mrfusion 5y ago
So Toyota still uses nimh in its hybrids? Does that make them longer lasting?
- kube-system 5y ago
  They currently use some of both NiMh and Li-ion. Toyota is notoriously conservative when choosing technologies. My guess is they still use a lot of NiMH because they have proven long-term reliability, more forgiving characteristics in harsh use, and they already have a lot of existing tooling to support them. If there any single car that has made the general public comfortable with very expensive batteries in their car: it’s the Prius.
  - ButchC 5y ago
    All those things are true when comparing NiMH to NiCd but definitely not compared to lithium batteries. There's not a single metric for which you can't find a superior suitable lithium chemistry. Except for one: $Cost Just Toyota doing Toyota things. Also I would strongly disagree on the Prius comment. A lot of "HV battery fault" cars out there back in the day, refurbing them was a pretty good business for a while. The NiMH pack in the Prius was the basis for so many slack jawed comments "EVs will never work! You're just going to have to replace the battery every 5 years!"
    - kube-system 5y ago
      Cost, as you mentioned, is one reason. However they also fare better at extended temperature ranges and under long periods of self discharge. They are, generally speaking, more forgiving of a battery chemistry. Your quote about rollout of the Prius is exactly my point. That opinion was widespread when the Prius was introduced. The reliability of the Prius since then has changed public opinion greatly.

vardump 5y ago

Isn't cylindrical form factor simply easier and cheaper to manufacture? Decades of industry experience manufacturing a ton of cylindrical products.

stetrain 5y ago

My understanding is Tesla currently uses cylindrical cells for NCA packs and blade/prismatic cells for LFP battery packs.

konspence 5y ago

How would a cylindrical shape isolate thermal runaway to one cell?

snovv_crash 5y ago
During fire they vent from one end, not in the middle. So this directs any flames away from adjacent cells.