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18650 Battery Improvements

There is general agreement that the 18650 battery used in the Roadster and Model S is old technology, but it continues to be used because improvements in capacity have kept it viable. It appears that the Roadster used a 2200mAh version of the 18650 cell and the Model S uses a battery with 3100mAh capacity. Given that 5300mAh versions of the 18650 battery are reportedly on the market, we could have an EPA range of 450 miles in a Model S without any change in the overall size of the battery pack.

I fully recognize that the 5300mAh capacity is apt to be marketing hype and am aware that the Chinese have often overrated the capacity of their batteries, but I gotta think that Tesla is going to pour a lot of research into this old technology as they begin to build the gigafactory. Teslas with greater range are coming.
 

ElSupreme

Model S 03182
Moderator
Jan 13, 2012
4,303
105
Atlanta, GA
18650 isn't really a technology, it is a form factor.

It would be like saying my home server is old technology, because it is built in a case from 1996. When it happens to be quite modern.

There are significant advantages to using many small Li-Ion cells, as well as some drawbacks. I think Tesla is correct in thinking that thousands of tiny cells is better overall than tens of large cells. The 18650 was a good starting point for that philosophy. And unless Tesla starts controlling their entire battery production they need to leverage a form factor that others can produce.
 
There is general agreement that the 18650 battery used in the Roadster and Model S is old technology, ....

There is not "general agreement" on such a thing. There is a heck of a lot fundamentally right with a cylindrical cell such as they way it is symmetrical about the center axis which makes the center convenient for an electrode. Much the same as an old-technology tire is round making the center a convenient location for a hub or axle.

Can't pack as much material in cylinders in the same space as one could with boxes. But then again if one needs to pass coolant around the cells the space between cylinders does nicely. The cylinders naturally only touch in 4 or 6 narrow places without need of spacers.
 

Cosmacelf

Well-Known Member
Supporting Member
Mar 6, 2013
10,259
30,828
San Diego
Tesla uses a proprietary internal cell chemistry to optimize longevity and power/weight density. There are lots of new chemistries and research papers that come out, and you can be sure that Tesla tests all the truly promising ones. Almost all new cells aren't suitable for Tesla due to longevity. Under real world conditions, they quickly degrade after just dozens of charge/discharge cycles.
 
Actually, the NCA-chemistry in the Model S-batteries are superior to all other EVs when it comes to longevity and energy output, however: Safety (risk of fire) and price is the major concerns. The Tesla Roadster uses different battery-chemistry that are inferior to Model S. According to the spider-charts at batteryuniversity the Roadster and Leaf har av 3\5-rating on longevity, but better ratings at safety. Model S har 5\5 on longevity.

A new type of battery that cope with higher and lower temperatures better and has an outstanding safetyprofile is the titanium-based li-ions. However, the cost is sky-high...
 

ItsNotAboutTheMoney

Well-Known Member
Jul 12, 2012
12,452
11,031
Maine
Tesla Motors CTO talks future batteries and charging protocols - SAE International

SAE interview with JB Straubel said:
Is Tesla still wedded to the 18650-form-factor cell? Are you looking beyond it?

For the immediate future we see 18650 as the most compelling. Believe me, we challenge it constantly. It always ends up being very controversial, for reasons I don’t totally understand. Nobody gives a damn about the shape and size of your fuel tank! But for some reason the shape and size of what you put your chemicals in to carry your energy in an EV is super controversial. What people should really debate is what are the nature of the chemicals inside; they’re what determines the cost and performance.

Please read that interview.

There is general agreement that the 18650 battery used in the Roadster and Model S is old technology, but it continues to be used because improvements in capacity have kept it viable. It appears that the Roadster used a 2200mAh version of the 18650 cell and the Model S uses a battery with 3100mAh capacity. Given that 5300mAh versions of the 18650 battery are reportedly on the market, we could have an EPA range of 450 miles in a Model S without any change in the overall size of the battery pack.

I fully recognize that the 5300mAh capacity is apt to be marketing hype and am aware that the Chinese have often overrated the capacity of their batteries, but I gotta think that Tesla is going to pour a lot of research into this old technology as they begin to build the gigafactory. Teslas with greater range are coming.

Tesla's cell densities are not bleeding edge since they're all about cost-effectiveness. But they're really only one generation behind the leading standard density cell.

Other companies have a different approach to Tesla and focused more on larger cells because they believe that it will minimize costs in the long run sincefewer cells means simpler, cheaper integration. But Tesla is much more focused on the short term and, having solved the engineering problems of integrating large numbers of cells benefit from the lower manufacturing costs with 18650. Tesla also has Panasonic manufacture a modified cell, which eliminates some of the expensive parts of the cell that Tesla doesn't need because it has active management in its battery.

Elon Musk has said in the past that the optimal cell for cost-effectiveness would probably be twice the size of 18650. That would provide the right balance between yield and integration cost. In explainingthe I, portance of yield for cost effectiveness he said to imagine that the battery had one huge cell: the high failure rate would make it cost prohibitive. But at the moment 18650 is the standard cell for factor so that's what they used. It's quite likely that they're working on the larger form factor for the Gen 3 cells since the at thst point whatever Tesla uses would be the most common form factor.
 
Elon Musk has said in the past that the optimal cell for cost-effectiveness would probably be twice the size of 18650. That would provide the right balance between yield and integration cost. In explainingthe I, portance of yield for cost effectiveness he said to imagine that the battery had one huge cell: the high failure rate would make it cost prohibitive. But at the moment 18650 is the standard cell for factor so that's what they used. It's quite likely that they're working on the larger form factor for the Gen 3 cells since the at thst point whatever Tesla uses would be the most common form factor.

Plus its not as if the Model S is bound to the 18650. Big flat battery box could house most anything.
 
The other reason to stick with 18650 format comes from the way the modules are made up. Each cell is connected with a small wire which as well as providing the electrical connection also acts as fuse. If for some reason the cell develops a fault and draws more current than it should, the fuse link 'blows', disconnecting that *one cell* from the module. The result has negligible affect on the pack as a whole but prevents a runaway thermal event - the main safety-related concern with using this type of cell.

On a larger cell format pack, to enable the same degree of cell-level control would be difficult (and have significant effect on the performance of the vehicle) to impossible. So, the very nature of the 18650-based design provides serious benefits that at first glance are not at all obvious and which, overall, far outweigh the down sides of the pack design. To my mind, this design choice is one of the fundamental reasons Tesla will lead the EV automotive world (and also revolutionise the national grid system - but that's another story) for a very long time. MW
 
When they build their new factory they could introduce a whole new form - say, a "stick" battery that has the same diameter as a 18650, but is twice or three times as long. I imagine that would make production considerably cheaper, you could maintan much of the cooling System, you would require only a third of the elctrical Connections, the battery would be lighter than two or three single cells and have more capacity too. And, best of all, you could still use it in some of the applications that so far require several 18650s
 

ItsNotAboutTheMoney

Well-Known Member
Jul 12, 2012
12,452
11,031
Maine
When they build their new factory they could introduce a whole new form - say, a "stick" battery that has the same diameter as a 18650, but is twice or three times as long. I imagine that would make production considerably cheaper, you could maintan much of the cooling System, you would require only a third of the elctrical Connections, the battery would be lighter than two or three single cells and have more capacity too. And, best of all, you could still use it in some of the applications that so far require several 18650s

The length of the cell impacts battery height and with a skateboard design they wouldn't want the battery to be too high. Elon Musk has suggested twice the size of cell, presumably fatter.
 
The length of the cell impacts battery height and with a skateboard design they wouldn't want the battery to be too high. Elon Musk has suggested twice the size of cell, presumably fatter.

They could simply pack the cells into the skateboard horizontally ...

fatter cells would have more volume per square inch of heavy metal casing and thus have a better kwh/weight ratio, 'tis true, but they would also make cooling more difficult because heat transfer to the outside would take longer. And you couldn't use them for 18650 applications any longer.
 

jkirkebo

Model S P85+ VIN 14420 EU
Jun 13, 2010
961
13
Fredrikstad, Norway
The length of the cell impacts battery height and with a skateboard design they wouldn't want the battery to be too high. Elon Musk has suggested twice the size of cell, presumably fatter.

The 26650 form factor already exists, might be a logical choice. Same height, 26mm width instead of 18mm. A little over twice the volume of the 18650.
 

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