3 ms·

This doesn't explain why LiPoly batteries are cuboids.

jacquesm 12y ago
Indeed it does not, this is about Tesla's and Panasonics 'gigafactory' which will make Lithium-Ion batteries in a cylindrical form factor. Lithium Polymer batteries (or LiPo for short) are a special case of Lithium-Ion batteries. They are sold in a 'pouch' format (and they are not the first to use a format like that, for instance, in the polaroid cartridges there used to be a battery in a similar form factor (polapulse)). The reason why LiPo batteries are not so constrained in shape as their siblings is that the electrolyte is a liquid. Solid electrolyte batteries are typically much more constrained in terms of shapes. This is also why regular car batteries (lead-acid) can be block shaped, the acid is also a liquid. The polapulse was an interesting battery, it only had to fire the camera 10 times but was quite high current. The packaging constraints of the cartridge dictated the battery geometry and so a flat pouch like battery was born. LiPo batteries exist in all kinds of interesting shapes and sizes too.
- tobz 12y ago
  Also, and this is entirely speculation and I'd love to hear a battery engineer confirm this, but: if you're packaging together cylindrical batteries, it inherently gives you more air channels between the batteries to promote cooling. When you're talking tens of kilowatts, both in discharge and charge rates, the percentage that ends up as waste heat suddenly becomes a whole lot of heat. You probably wouldn't want a maximally stuffed cavity with these packs turning into a single, massive chunk of thermal mass. EDIT: looks like I was firsted somewhere below, doh!
  - jacquesm 12y ago
    But you're 100% on point there. That's a side benefit from having those cylindrical cells.
- TD-Linux 12y ago
  This is exactly backwards. Traditional Li-Ion batteries have a liquid electrolyte, and Li-Poly have a solid polymer electrolyte. Both batteries consist of anode/electrolyte/cathode rolled up. In the case of a "pouch" cell, they are rolled up flat, and a cylinderical cell has them rolled up in a cylinder. There is actually no limitation for the shape - you can totally make a Li-ion battery with liquid electrolyte in a prism - many cell phone batteries do this. Li-ion, due to the liquid, needs a hard metal case, whereas li-poly can often get away with a foil pouch. The surface area per volume of a cylinder is less, as well as easier to make structurally sturdy, which means less weight is spent in the casing. Tesla cares more about weight than volume, so this is an acceptable tradeoff.
  - jacquesm 12y ago
    Interesting! I just spent the better part of today reading up on all this because I found it hard to accept that I'd remember something so terribly wrong. Turns out that the names have changed over time to denote various packages and gel/liquid/solid combinations. Wikipedia has a whole page on the subject and it almost seems as if they made the naming of these battery classes confusing on purpose: http://en.wikipedia.org/wiki/Lithium_polymer_battery http://en.wikipedia.org/wiki/Lithium_polymer_battery Enjoy the read, I certainly did and it turns out the situation is a lot more complex (also historically) than I remembered it, but my memory wasn't quite as faulty as you made me feel initially (fortunately!).

Indeed it does not, this is about Tesla's and Panasonics 'gigafactory' which will make Lithium-Ion batteries in a cylindrical form factor. Lithium Polymer batteries (or LiPo for short) are a special case of Lithium-Ion batteries. They are sold in a 'pouch' format (and they are not the first to use a format like that, for instance, in the polaroid cartridges there used to be a battery in a similar form factor (polapulse)). The reason why LiPo batteries are not so constrained in shape as their siblings is that the electrolyte is a liquid. Solid electrolyte batteries are typically much more constrained in terms of shapes. This is also why regular car batteries (lead-acid) can be block shaped, the acid is also a liquid. The polapulse was an interesting battery, it only had to fire the camera 10 times but was quite high current. The packaging constraints of the cartridge dictated the battery geometry and so a flat pouch like battery was born. LiPo batteries exist in all kinds of interesting shapes and sizes too.

tobz 12y ago
Also, and this is entirely speculation and I'd love to hear a battery engineer confirm this, but: if you're packaging together cylindrical batteries, it inherently gives you more air channels between the batteries to promote cooling. When you're talking tens of kilowatts, both in discharge and charge rates, the percentage that ends up as waste heat suddenly becomes a whole lot of heat. You probably wouldn't want a maximally stuffed cavity with these packs turning into a single, massive chunk of thermal mass. EDIT: looks like I was firsted somewhere below, doh!
- jacquesm 12y ago
  But you're 100% on point there. That's a side benefit from having those cylindrical cells.
TD-Linux 12y ago
This is exactly backwards. Traditional Li-Ion batteries have a liquid electrolyte, and Li-Poly have a solid polymer electrolyte. Both batteries consist of anode/electrolyte/cathode rolled up. In the case of a "pouch" cell, they are rolled up flat, and a cylinderical cell has them rolled up in a cylinder. There is actually no limitation for the shape - you can totally make a Li-ion battery with liquid electrolyte in a prism - many cell phone batteries do this. Li-ion, due to the liquid, needs a hard metal case, whereas li-poly can often get away with a foil pouch. The surface area per volume of a cylinder is less, as well as easier to make structurally sturdy, which means less weight is spent in the casing. Tesla cares more about weight than volume, so this is an acceptable tradeoff.
- jacquesm 12y ago
  Interesting! I just spent the better part of today reading up on all this because I found it hard to accept that I'd remember something so terribly wrong. Turns out that the names have changed over time to denote various packages and gel/liquid/solid combinations. Wikipedia has a whole page on the subject and it almost seems as if they made the naming of these battery classes confusing on purpose: http://en.wikipedia.org/wiki/Lithium_polymer_battery http://en.wikipedia.org/wiki/Lithium_polymer_battery Enjoy the read, I certainly did and it turns out the situation is a lot more complex (also historically) than I remembered it, but my memory wasn't quite as faulty as you made me feel initially (fortunately!).