8 ms·

That's interesting and somewhat surprising. I'm not knowledgeable about battery design by any means, but I would have thought that there would be a better way t

That's interesting and somewhat surprising. I'm not knowledgeable about battery design by any means, but I would have thought that there would be a better way to make a battery pack for a car than connecting thousands of small batteries together.

tppiotrowski 4y ago
It's often not the best design but the one that's cheap, scalable and has momentum behind it that wins out.
ggm 4y ago
if I remember my basic chemistry, batteries don't deliver voltages at the level of 10/20/100v directly often, its more commonly 1/2v or 0.5v class voltages. You have to have a much more 'aggressive' chemical reaction to deliver higher voltages. And, the same with current: a single surface between two reacting things delivers less current. Its a function of surface area. Same with capacitance: you sometimes need 'more' surface to big up the effect. Therefore all you have is stacking it up. parallel or serial, thats what there is to get higher voltages, more current draw, longer life per-cell. Inside a lead acid battery its multiple surfaces, sub-cells. It's normal. inside almost any domestic battery I suspect its sub-cells, sub-cells all the way down. A giant roll of surface, to increase the area in contact might be one way of getting "more" in terms of current draw or lifetime. I bet that its voltage remains close to the constant in this, hence Tesla "stacking" up the rolled cells, to boost voltage.
- rbanffy 4y ago
  > Inside a lead acid battery its multiple surfaces, sub-cells. IIRC, “battery” used to be the technical term for “a bunch of connected power cells”.
  - ggm 4y ago
    Yes. A battery of guns isn't usually just one. It's a set word. The singleton would be cell.
MobiusHorizons 4y ago
This strategy is one of the remarked upon things when I first heard of Tesla (something like “this California startup is powering their electric car with laptop batteries”) ironically laptops have almost all transitioned to lithium polymer (pouch cells) instead of the 18650s they used back then. Not all car manufacturers use teslas standardized cell technique, as it does have some downsides. I guess time will tell, but I doubt Tesla will abandon this technique any time soon.
CarVac 4y ago
Smaller cells are safer due to better containment of thermal runaway, letting them use a better-performing but somewhat riskier cell chemistry.
Bayart 4y ago
Using standard form factors and manufacturing techniques made it much easier for Tesla to get batteries off the ground through their partnership with Panasonic. The extra space left by the gaps between cells also has the advantage of being ideal for cooling (battery performance and safety is correlated to temperature).
pjc50 4y ago
Separating the cells allows makes it easier to cool them. It also provides more inert metal between them in case of fire. A certain amount of stacking is necessary to get up to a decent voltage, as others have pointed out. But even "100 brick-sized cells" would be a more dangerous prospect than "thousands of 18650 cells".
michaelt 4y ago
The Nissan Leaf uses larger cells [1], each roughly the size of a ream of printer paper. So there are real car designers who agree larger batteries are worth considering. Of course, the Leaf makes a bunch of other decisions that are different to Tesla - lower price point, smaller battery/reduced range, air-cooling batteries instead of water-cooling, a (now abandoned) battery lease scheme, and suchlike. [1] https://www.google.com/search?q=nissan+leaf+cell&tbm=isch https://www.google.com/search?q=nissan+leaf+cell&tbm=isch

tppiotrowski 4y ago

It's often not the best design but the one that's cheap, scalable and has momentum behind it that wins out.

ggm 4y ago

if I remember my basic chemistry, batteries don't deliver voltages at the level of 10/20/100v directly often, its more commonly 1/2v or 0.5v class voltages. You have to have a much more 'aggressive' chemical reaction to deliver higher voltages. And, the same with current: a single surface between two reacting things delivers less current. Its a function of surface area. Same with capacitance: you sometimes need 'more' surface to big up the effect. Therefore all you have is stacking it up. parallel or serial, thats what there is to get higher voltages, more current draw, longer life per-cell. Inside a lead acid battery its multiple surfaces, sub-cells. It's normal. inside almost any domestic battery I suspect its sub-cells, sub-cells all the way down. A giant roll of surface, to increase the area in contact might be one way of getting "more" in terms of current draw or lifetime. I bet that its voltage remains close to the constant in this, hence Tesla "stacking" up the rolled cells, to boost voltage.

rbanffy 4y ago
> Inside a lead acid battery its multiple surfaces, sub-cells. IIRC, “battery” used to be the technical term for “a bunch of connected power cells”.
- ggm 4y ago
  Yes. A battery of guns isn't usually just one. It's a set word. The singleton would be cell.

MobiusHorizons 4y ago

This strategy is one of the remarked upon things when I first heard of Tesla (something like “this California startup is powering their electric car with laptop batteries”) ironically laptops have almost all transitioned to lithium polymer (pouch cells) instead of the 18650s they used back then. Not all car manufacturers use teslas standardized cell technique, as it does have some downsides. I guess time will tell, but I doubt Tesla will abandon this technique any time soon.

CarVac 4y ago

Smaller cells are safer due to better containment of thermal runaway, letting them use a better-performing but somewhat riskier cell chemistry.

Bayart 4y ago

Using standard form factors and manufacturing techniques made it much easier for Tesla to get batteries off the ground through their partnership with Panasonic. The extra space left by the gaps between cells also has the advantage of being ideal for cooling (battery performance and safety is correlated to temperature).

pjc50 4y ago

Separating the cells allows makes it easier to cool them. It also provides more inert metal between them in case of fire. A certain amount of stacking is necessary to get up to a decent voltage, as others have pointed out. But even "100 brick-sized cells" would be a more dangerous prospect than "thousands of 18650 cells".

michaelt 4y ago

The Nissan Leaf uses larger cells [1], each roughly the size of a ream of printer paper. So there are real car designers who agree larger batteries are worth considering. Of course, the Leaf makes a bunch of other decisions that are different to Tesla - lower price point, smaller battery/reduced range, air-cooling batteries instead of water-cooling, a (now abandoned) battery lease scheme, and suchlike. [1] https://www.google.com/search?q=nissan+leaf+cell&tbm=isch https://www.google.com/search?q=nissan+leaf+cell&tbm=isch