Forums

JOIGNEZ-VOUS À LA COMMUNAUTÉ
INSCRIVEZ-VOUSIdentifiant

Battery Chemistry

Hi all,
I was just wondering what the battery chemistry was in the Model S. I know that it is different for the 40kwh/60kwh and 85kwh battery packs. Just wondering so I can do some research on the reliability of the Cell chemistries. I'm pretty sure it's been posted in the forum before but I can't find it.

Many people say it is standard Panasonic battery, but a Tesla person who should know told me it is actually custom made to Tesla specifications. I did not ask for the exact chemistry.

The 60 and 85 cells may well be identical. Someone suggested there was a late change to the 40s so it too is using the 18650. TM isn't saying.

Logic and data suggests all 3 models use the same cell type and Lithium Ion chemistry, just a different number of cells.

85 kWh uses Panasonic NRC 18650A 3.1Ah - you can find easy the spec sheet just google it - it is an automotive battery whith additional features to reduce the chance of thermal run away and current overload.
60 kWh not clear here - may be using Panosonic 2.1 Ah battery same as in the roadster. This is an older design.
40 kWh - no clue
What TM is actually using depends on the supply available. Panasonic is the best, maybe Sanyo but not much beyond that. Some other brands you find are just repackaged Panasonic batteries. Many other brands are just not suited for this application.

As previously posted elsewhere, Jan 25, 2013 email response from my Tesla rep about type of batteries in the 60 kWh cars vs the 85 kWh cars confirms they are the same batteries:

As for the battery cells, the 60kWh uses the same cell type as the 85kWh battery, but less of them.

Kleist
Panasonic bought Sanyo.

For the 40, i am going with the same cells, less than 4,000 of them, and roughly 4200 pounds curb weight.

I'll buy dinner if anyone wants to bet against those numbers and wins.

I do know for certain that what Panasonic sells Tesla is custom. How custom, I don't know. I also know that the 85 and the 60 batteries are the same. Regarding the 40, it will be different, as Tesla is going to try to reduce costs. Whether the first 40 cars shipped will be different, I don't know.

@Hills - do you have an 'unnamed source'? You seem mighty confident about some of your postings. You don't happen to have a TM employee in the family, do you? ;-)

When I am certain, I say so. When I am not, I also say so. No employee in the family. No close friend who is employee. Longer history of watching this company than most people on this forum, that is all.

Some problems that have to be considered it the amount of current that needs to be drawn out or pushed back into each cell. Panasonic 18650 cells have a high enough resistance that this can cause thermal problems with the cells.

Perhaps they will space the same cells apart to provide more cooling to each cell. They could go with more cells of a lower capacity.

One thing to consider is that they spent a lot of time vetting the cell they choose (years of testing) and they aren't going to change to something new or untested.

If I where to bet, I would go with same cells, only less of them spaced apart with better cooling. Motor controller current limits naturally turned down on both discharge and regen. Different firmware tweaks for charging profile and internal cell balancing. Oh and they can reduce the voltage output of the stack since voltage only gets you a higher RPM out of the motor, so they can take cells out from a series configuration and put them in parallel as they reduce the total number.

My reason for expecting the same cells in the 40 is purely deductive logic, based in the available data that is known at this moment. The factors that point to this are:

1. The purchasing leverage that comes with buying high volume of exactly the same cell for all models.

2. The engineering workload reduction by only needing to characterize and validate charge, discharge, and thermal performance of only a single cell type.

3. The cost reduction for the BOM is likely better with fewer of the high grade cells, rather than more of some cheaper cells. This is because there are many nontrivial costs to connect, house, and protect each cell. Many more cheap cells would actually have much more total overhead cost, compared with the smallest number of high grade cells that can do the job.

4. Fewer cells is lighter. This will likely allow better overall system efficiency to achieve the desired range and dynamic driving performance.. TM engineers are maniacal and meticulous about efficiency optimization.

So absent a statement by TM otherwise, it seems that this is the most probable inference one can make.

My reason for expecting the same cells in the 40 is purely deductive logic, based in the available data that is known at this moment. The factors that point to this are:

1. The purchasing leverage that comes with buying high volume of exactly the same cell for all models.

2. The engineering workload reduction by only needing to characterize and validate charge, discharge, and thermal performance for all packs built from a single cell type.

3. The cost reduction for the BOM is likely actually better with fewer of the high grade cells, rather than more of some cheaper cells. This is because there are many nontrivial costs to connect, house, and protect each cell. Many more cheap cells would actually have much more total overhead cost, compared with the smallest number of high grade cells that can do the job.

4. Fewer cells is lighter. This will likely allow better overall system efficiency to achieve the desired range and dynamic driving performance.. TM engineers are maniacal and meticulous about efficiency optimization.

So absent a statement by TM otherwise, it seems that this is the most probable inference one can make.

Sorry for double post glitch.

Cmeyers - agree with most of your assumptions, but I imagine a different config for the smaller number of cells.

I think they will use the same cell spacing matrix, but not populate certain locations. For example there is a hump area near the front of the pack that a TMer said was to house more cells. If true. they could eliminate that subassembly entirely and reduce cost.

The reason for sticking with the same density is that it is already validated and optimizes many different detailed factors like wirebond fuselinks, current densities in the busses, etc.

Farther apart may give more thermal safety margin, but TM already achieved full protection against chain reaction, so it's better not to have to re-optimize all those other details again.

@ Hill - do you know if the custom nature, whatever it is- was part of the Tesla patent submittals to protect it by any chance. I was told they certainly patented the other (packaging-cooling-fusing) parts. I'm curious how deep into the cell the Tesla uniqueness is protected

@kenilles, I don't know for sure regarding how it is custom. My understanding is that the chemistry is somewhat custom rather than packaging cooling, as Panasonic to my knowledge does not provide anything other than the cell.

Jumping into the guessing game, I'll agree with Mark K. I think they will be using only one cell type for all configurations. I'll also guess that the only custom aspect of the cell is the marking on the outside. This alone would give it its own unique part number and make it nearly impossible to identify the chemistry and rating. TM may also have different testing requirements on their "custom" cells. Assuming the same configuration with just fewer cells the draw from the 40kWh is less than the draw from the performance so this should not be an issue.

Cell chemistries can change the cost of the system significantly. However using different electrode sheets in the cell I can't imagine adding much manufacture cost. So all we have is the elements Li and Nickel? usually you get a LiFePO4 or LiCoO2 or LiMnO4 or something.

Thank you for the link aschulz90

Type High Capacity Models (Ni System)
Nominal Voltage 3.6 (V)
Nominal Capacity (min.) 2750 (mAh)
Nominal Capacity (typ.) 2900 (mAh)

If the above is correct then at a fully charged voltage of 4.2 V you have 7000 cells * 4.2 volts * 2750 mAh / 1000 = 80850 Wh or 80.85KWh which would make sense.

It would be nice to know the C rating for both charge and discharge.

If you look at some of the presentations done by Tesla Battery engineers dating back to 2006 they say that they don't charge above 4.15 (range charge) and above 4.1 (normal charge) to protect the life of the battery.

goken1's surmise sounds right. Very likely the only thing custom about the cell is the customer part number and perhaps a test methodology.

Even if TM collaborated and pushed Panasonic to advance certain qualities, Panasonic would need to retain rights, in order to offer their best know-how to the largest possible market.

I think these are effectively stock cells.

TM's secret sauce is in how they array them, package them, and manage them (both thermally and electrically). Nobody I know of even comes close to TM's sophistication on these metrics. There are also a ton TM patents on this technology.

In the future, I believe TM will eventually also contribute significant advances in the state of the art for the storage cells themselves, particularly when composites of chemical batteries and super capacitors become practical at a micro or nano scale. This is of strategic significance to their business plan.

Such hybrid storage elements will ultimately bring dramatic advances in charge time, capacity, internal impedance, and cell life.

Perhaps 10 years from now, when your Model S could use a new pack, you'll be able to bolt in one of these nextgen nanopacks, and give your car startling new superpowers.

You may feel like teenager once more, all over again.

Yes, THAT hybrid technology has a future.

@nickjhowe

Thank you for your comment. I agree I would not want to charge above 4.15. Also true that Panasonic rates the "typical" Capacity is 2900mAh hence the actual capacity could be as high as 84.245 KWh
As always the actual capacity would probably be somewhere in between but with that we are close to the advertised 85KWh.
It would be nice to know the C rating for both charge and discharge.

Also I think I found the information about the C rating which Panasonic defines as "lt" and they recommend a no higher than 0.7 lt which basically means 1/7 of total amperage of the battery pack.
That value goes down to 0.1 lt for batteries discharged down to 3.1 volts.

Agiangone -

0.7 C = 70% C = 0.7 X 85 = 59.5kW charge rate

C is a constant reflecting the battery's ability to hold charge, and is invariant with current state of charge, which changes the cell potential to a lower voltage.

So at 3.6V, the SOC is much lower than at 4.1V.

Cells should never have an open circuit (unloaded) potential of 3.1V. If so, the battery would be ruined, so manufacturers like TM have cutoff systems to prevent this.

Hi Mark,

do you happen to know how the cells are wired together? or in other words, what voltage do they output to the controller?

Apocryphal info on this, but there are suggestions that the cells are in clusters of about 100. If those are in series for discharge, that'd be around 400 volts. That sounds like it's also the motor winding drive voltage, so one can imagine an efficient PWM current management scheme without a step-up or down during drive. More hard data is needed on this though - mostly speculation right now. There are many ways they could array the cells, including dynamic rearrangement for different modes.

This Tesla Press Release from 2010 says that they were using the NCR18650A battery from Panasonic.

It links to this press release from Panasonic that includes these specs:

Model                       NCR18650         NCR18650A
                       s(Current Model)    (New High Capacity Model)
Capacity                    2.9 Ah            3.1 Ah
Volume energy density      620 Wh/L         675 Wh/L
Diameter               18.6 +0/-0.7 mm   18.6 +0/-0.7 mm
Height                 65.2 +0/-1.0 mm   65.2 +0/-1.0 mm
Mass                   Approx. 44 g      Approx. 44.5 g
Voltage                    3.6 V             3.6 V
Charging voltage           4.2 V             4.2 V
Energy                    10.4 Wh            11.2 Wh

Detailed specs including charge/discharge curves can be found here: http://industrial.panasonic.com/www-data/pdf2/ACA4000/ACA4000CE254.pdf

BUT - and it's a big but - here's a video of Elon where he specifically states that they do NOT use off-the-shelf 18650 cells and that they've worked with Panasonic to produce a unique cell for Tesla Model S that uses the 18650 form factor. http://www.youtube.com/watch?feature=player_detailpage&v=9cfHGDoniU0#t=169s

Believe the video. However, why does it matter if the Model S battery is functional and safe, unlike that infamous jumbo jet?

Good digging Njck. Elon was pretty explicit about asserting that they pushed Panasonic to optimize cells for their purposes.

So one could imagine modified electrode structures or electrolyte doping for their automotive objectives.

My guess is that this would be in the form of Elon guiding Panasonic engineers to new strategies and specs. If TM had patents in this area, they might command exclusivity, but my guess is that it might have instead been part of the package of consideration for Matsushita's investment.


X Deutschland Site Besuchen