Tesla Model S 18650 Cell Test Data

[Punx0r]

Interesting recovery of the discharged cell. Is the particular chemistry more tolerant to it than is typical for li-ion? I recall mentions of nasty side reactions, like copper being consumed at low voltages. Any plans to cycle that cell?

 

[okashira]

Interesting recovery of the discharged cell. Is the particular chemistry more tolerant to it than is typical for li-ion? I recall mentions of nasty side reactions, like copper being consumed at low voltages. Any plans to cycle that cell?

Yep, I will cycle it this weekend.

 

[flathill]

0V test now at .....

I should have set the multimeter to log to see just how much capacity comes from the cells all the way down to 0V. :-/

It's been nearly a year since I put these cells in the 0V storage test.
I disconnected the resistor about a month ago and voltage still read about 0.002V.
Over the past month, the cells increased in voltage to about 0.4V.

I went ahead and hooked up one to my tester and charged it with 0.1A to 2V, then 0.3A to 2.8V, then 0.5A to 4V. Then I let the cell rest to see if voltage dropped. Nope, held 3.99V like a champ.
Went ahead and charged to 4.2V with 0.1A cut. And ran a 3A discharge.
The cell showed like 94% full capacity, maybe DCIR picked up a little bit. However, it still holds a charge and works great. I'll run a few more cycles soon.

VERY IMPRESSIVE. THANK YOU FOR PERFORMING THIS TEST

 

[Cephalotus]

A look at the warranty on Tesla powerwall systems is quite interesting:

They use two cell types, a NMC cell for daily storage and a NCA cell (I'm assumeing the same as in the Tesla S) for the "weekly storage" system:

NMC cell:

>60% of its initial rated capacity until the earliest to occur of:
(a) The lithium-ion battery cells in the Product have reached 18 MWh of aggregate discharge throughput (at the battery DC output); or
(b) 10 years have expired from the Original Installation Date.

This is around 2800 cycles at 90% DOD

NCA cell:

The Product shall maintain >60% of its initial rated capacity until the earliest to occur of:
(a) The lithium-ion battery cells in the Product have reached 4 MWh of aggregate discharge throughput (at the battery DC output); or
(b) 10 years have expired from the Original Installation Date; or
(c) The Product has been placed in off-grid mode one hundred times, or has spent 2400 hours in off-grid mode.

This is just around 400 cycles at ???% DOD.

Or just 100(!) cycles at 100% DOD or just 2400 hours at 0% SOC. (this is more likely 2,5V than 0V)

Not so spectacular imho. (and also not very promissing for Tesla S drivers)

http://solarenergysystems.baywa-re.com/media/filer_public/9b/fd/9bfd7dfa-ad37-41bc-9c3f-191c2c8349db/powerwall_manufacturers_warranty_certificate_germany_final.pdf

 

[okashira]

?

...Cool story.

 

[Occam's Laser]

A look at the...

Somebody is short TSLA.

 

[randyc1]

What Voltage Range (charged , dis-charged) would be ideal using a 10s4p battery pack with these Tesla batteries?

 

[okashira]

Depends on your goals and needs

But I'd start by charging to 4.05V (40.5V) then see how the range works for you.

Stop at 2.8V (28V) total shut off

Charge at every opportunity. Don't run the pack down needlessly.

If you need more range, charge to 4.1V or 4.2V.

 

[MitchJi]

They use two cell types, a NMC cell for daily storage and a NCA cell (I'm assumeing the same as in the Tesla S) for the "weekly storage" system:

Not the same. Very similar chemistry.

 

[DasDouble]

So is it better then Samsung 30Q or Sonys 3500mAh cell?

Cheers

 

[Hillhater]

The indications are that Tesla push these cells to 7C (20+ Amps) in the S for brief periods.
Do we know what the output limit is for say 3-5 secs ..dead short Maybe ?
Im guessing it might be 40-50A, but only at a voltage of around 2 volts ?
..anyone done the test ?

 

[Pajda]

I can do this kind of test (up to 40A), but I am more interested in standardized cycle life test and finaly compare it to commnon industrial 18650 cells which I have already tested. But I am not able to find someone who already done this tests or who can sell and send me 4-8 samples to EU with standard shipping costs, because most of them are in the US.

 

[okashira]

The indications are that Tesla push these cells to 7C (20+ Amps) in the S for brief periods.
Do we know what the output limit is for say 3-5 secs ..dead short Maybe ?
Im guessing it might be 40-50A, but only at a voltage of around 2 volts ?
..anyone done the test ?

What are you tying to learn? There are so many variables involved.
For example... Tesla's cells are especially temperature sensitive. I think this is part of their "secret sauce,"

Their DCIR drops significantly at higher temps up to 55°C or so, and is much higher at lower temps.
Perhaps they traded off low temp performance for high temp performance, and as a result, they are more durable at higher ambient temps. This makes sense as a battery will always be above ambient temps and it's easier to heat then cool.

On a dead short you might get 35A at 10°C, and 100A at 50°C. Just a quick back of napkin guess from what i have seen from dcir testing

 

[madin88]

Their DCIR drops significantly at higher temps up to 55°C or so, and is much higher at lower temps.
Perhaps they traded off low temp performance for high temp performance, and as a result, they are more durable at higher ambient temps. This makes sense as a battery will always be above ambient temps and it's easier to heat then cool.

That would make sens. most batteries have such properties. not only tesla cells.
higher temperatures means the chemical process will go faster which obviously leads to lower resistance.

the downside is the ageing happens quicker at higher temperatures.

 

[Pajda]

Yes, but for Tesla's cells this phenomenon is far more pronounced than with the common industrial 18650 cells.

 

[Hillhater]

^^^^..how pronounced ?
I believe the "nominal" IR of the Tesla cell is about 40mOhm ( @ room temp) , but how much lower does it get ?
Without an actual "near short" discharge test, i guess the IR is a good indicator of "burst" discharge from these cells.
(In the way that Samsung have reported "burst" ..1-2 sec... Discharge levels of 100 A for some of their cells )
Even at 40 mOhm , its a fair guess the cell could be capable of 50+ amps for a few seconds !
Really, all i am trying to guess is how much further Tesla might push up the output from this existing cell to increase performance of the S and X , beyond current levels....if they wanted to ?
...ignoring any other hardware limitations. ...Such as fuseable connections etc !

 

[djeao]

0V test now at .....

I should have set the multimeter to log to see just how much capacity comes from the cells all the way down to 0V. :-/

It's been nearly a year since I put these cells in the 0V storage test.
I disconnected the resistor about a month ago and voltage still read about 0.002V.
Over the past month, the cells increased in voltage to about 0.4V.

I went ahead and hooked up one to my tester and charged it with 0.1A to 2V, then 0.3A to 2.8V, then 0.5A to 4V. Then I let the cell rest to see if voltage dropped. Nope, held 3.99V like a champ.
Went ahead and charged to 4.2V with 0.1A cut. And ran a 3A discharge.
The cell showed like 94% full capacity, maybe DCIR picked up a little bit. However, it still holds a charge and works great. I'll run a few more cycles soon.

Wow, this is quite an interesting test! I know it's been a few years, but did you end up cycling the "presumably dead but seemingly still good" cell a few times? (either before putting it in 0V storage or after). Or was it just a one-time test? I wonder how many cycles it could withstand after it went to 0V without blowing up..