Battery Degradation Scientifically Explained

[scaesare]

Fast charge is typically used as short-hand for DC Fast Charging which is when the charger is outside the vehicle and provides DC power directly to the battery. It ranges from ~20kW to 350kW. Anything coming from single-phase AC power is not fast charging is very benign for the battery.

Typically DC fast charging("Level 3") starts at ~50kW rate.

The ~20kW rate you mentioned is considered "Level 2". This is possible on single-phase A/C circuits (i.e. a Tesla HPWC on a 240V/100A circuit).

 

[scaesare]

You are correct, however the Model 3 can still heat the battery. When parked, it runs power through the motor(s) in a fashion that just creates waste heat. It routes that heat to the battery with the coolant. It can also do this while driving and is noticeable by a slight whine from the front motor in an AWD. I understand that this process can use an extra 7kW parked and 4kW while driving in addition to normal heat generation from motive force losses. This amount of heat is very similar to the resistive battery heaters in the S/X and other EVs.

Do you have a references for the Model 3 using -7kW for heating?

I originally have seen estimates of 2kW... but that may have changed. Also not sure how the front motor contributes (if it can given it's an induction unit).

 

[Zoomit]

Typically DC fast charging("Level 3") starts at ~50kW rate.

The ~20kW rate you mentioned is considered "Level 2". This is possible on single-phase A/C circuits (i.e. a Tesla HPWC on a 240V/100A circuit).

There are many installed DC Fast Chargers that put out 55A or 60A. These typically provide around 20kW into 350V batteries at low SoC. These units are wall-mountable and often seen at car dealerships.

The SAE J1772 standard defines AC Level 2 as you describe but the their DC Levels have never entered the lexicon. Referencing DCFC as "Level 3", which first started with LEAF owners using CHAdeMO, seems to be dwindling as I see fewer new EV owners using that term. Thankfully, I might add, as it's never been a well-defined standard. Calling both 20kW and 350kW charging "Level 3" isn't really helpful.

Do you have a references for the Model 3 using -7kW for heating?

I originally have seen estimates of 2kW... but that may have changed. Also not sure how the front motor contributes (if it can given it's an induction unit).

Model 3 battery heating (ignoring the cabin heater) appears to be either 4 or 7 kW based on u/Wugz data on reddit: On-Route Battery Warmup Measured : teslamotors. The front motor sounds distinctively different when ORBW is in use, so I expect it is contributing in some fashion to the heating process.

 

[darth_vad3r]

Typically DC fast charging("Level 3") starts at ~50kW rate.

The ~20kW rate you mentioned is considered "Level 2". This is possible on single-phase A/C circuits (i.e. a Tesla HPWC on a 240V/100A circuit).

It’s a technicality, but as “fast charging” slows at end of charge with high SoC the power tapers dramatically ... it is still “fast charging” but at a slow rate

 

[darth_vad3r]

Do you have a references for the Model 3 using -7kW for heating?

I originally have seen estimates of 2kW... but that may have changed. Also not sure how the front motor contributes (if it can given it's an induction unit).

They run the rear motor with non-optimal parameters intentionally to generate waste heat. The rear motor is a permanent magnet variant. Not sure about the front one on AWD. Is that one induction? I thought the 3’s switched to the new style PM motors?

 

[Zoomit]

The attached figure shows the effect of calendar ageing for a typical Li-Ion cell due to SoC and temperature, (source: Calendar Aging of Lithium-Ion Batteries).

This is very interesting data. Do you have any reason to think the Panasonic/Tesla 2170 NCA cells perform differently than the 18650 cells in this study?

Based on this, it seems storage below 55% actual SoC is desirable. That translates to about 50% indicated SoC.

 

[scaesare]

There are many installed DC Fast Chargers that put out 55A or 60A. These typically provide around 20kW into 350V batteries at low SoC. These units are wall-mountable and often seen at car dealerships.

The SAE J1772 standard defines AC Level 2 as you describe but the their DC Levels have never entered the lexicon. Referencing DCFC as "Level 3", which first started with LEAF owners using CHAdeMO, seems to be dwindling as I see fewer new EV owners using that term. Thankfully, I might add, as it's never been a well-defined standard. Calling both 20kW and 350kW charging "Level 3" isn't really helpful.

My point was that you mentioned ~20kW as not available on single phase A/C. It is, as your own chart specifies.

As for DC charging, there are certainly multiple levels. But nobody rally considers ~20kW DC charging as Fast charging. There may be 20kW DC chargers installed... but they ain't "Fast".

Generally, 50+kW are what's typically considered a DC Fast charger. Unfortunately as you note, the official definitions are lacking.

Model 3 battery heating (ignoring the cabin heater) appears to be either 4 or 7 kW based on u/Wugz data on reddit: On-Route Battery Warmup Measured : teslamotors. The front motor sounds distinctively different when ORBW is in use, so I expect it is contributing in some fashion to the heating process.

Cool, thanks.

 

[scaesare]

They run the rear motor with non-optimal parameters intentionally to generate waste heat. The rear motor is a permanent magnet variant. Not sure about the front one on AWD. Is that one induction? I thought the 3’s switched to the new style PM motors?

I understand how the heat is generated, my question was on the power it could produce.

The 3 has PM rear motors. The fronts are induction... as a result the AWD's actually get slightly less efficient.

It's not clear to me if the induction motors can be biased to produce waste heat in the same way the SWPRM's can.

 

[darth_vad3r]

This is very interesting data. Do you have any reason to think the Panasonic/Tesla 2170 NCA cells perform differently than the 18650 cells in this study?

Based on this, it seems storage below 55% actual SoC is desirable. That translates to about 50% indicated SoC.

What are you basing 55% actual to 50% indicated on?

How much % of actual are you counting as (a) anti-brick, (b) below dashboard zero, and (c) above dashboard 100% buffers?

 

[darth_vad3r]

I understand how the heat is generated, my question was on the power it could produce.

The power “produced”? You mean the power consumed to generate the waste heat?

It's not clear to me if the induction motors can be biased to produce waste heat in the same way the SWPRM's can.

Ya, I have no idea. I don’t think they can in anywhere near as “efficient” (aka inefficient) manner as the PM motors. Why’d you bring up the front motors? Or did someone else? [EDIT: I see now you didn’t bring it up, but were querying in response to a post referring to reddit posts about AWD front motor “whine”. See my next post for a theory on this - it could be working harder for motion to make up for rear motor diverting power to heat]. My understanding was the rear motor is the one hooked into the battery warming system since it’s common to all trims.

 

[darth_vad3r]

The front motor sounds distinctively different when ORBW is in use, so I expect it is contributing in some fashion to the heating process.

It could not contribute directly to heating, but only indirectly by picking up some of the slack for motion that the rear motor is shunting towards heat.

e.g. P = amount of power required for motion. Let’s say this is split F+R normally for AWD.
1. RWD ORBW = rear motor works P + H more than usual to move car, to output heat in addition to movement.
2. AWD ORBW = rear motor works R + H more than usual to move the car, to output heat in addition to movement, but cuts back a smaller amount W normally used for motion which then the front motor works F + W more than usual for motion to cover the difference.

1) P vs P + H (P power for motion, H for heat)
2) F, R. vs. F+W, R+H-W (power for motion: F+W+R-W = F+R = P, power for heat = H)

“W” extra power contributes to front motor whine. [Shoot, I should have called it W. LOL. It was “Z”, ok I changed them all. LOL]

In this way both motors split the extra load, but the power balance shifts from rear to front a bit (for motion) while ORBW is on with all the “extra waste heat” coming from the rear motor.

This is just a theory. Are there tear downs or diagrams showing that the front motor is hooked into the cooling/heating system?

 

[Zoomit]

What are you basing 55% actual to 50% indicated on?

How much % of actual are you counting as (a) anti-brick, (b) below dashboard zero, and (c) above dashboard 100% buffers?

Just approximate numbers. Don’t overthink my comment as I basically rounded to the nearest 5%. I’d guess a) 4%, b) 2%, c) 0%

Are there tear downs or diagrams showing that the front motor is hooked into the cooling/heating system?

Of course, check the Tesla parts catalog. Both drive units have an oil to coolant heat exchanger being fed by coolant from/to the Superbottle.

 

[darth_vad3r]

Just approximate numbers. Don’t overthink my comment as I basically rounded to the nearest 5%. I’d guess a) 4%, b) 2%, c) 0%

Hmm, you really think they let us go to true 100? I haven’t read anything about this that I recall. I was guessing no.
I was guessing (b) was that infamous 4 kWh “energy buffer” and my theory on that is that it gets built up from 0 kWh at 100% SoC to ~4 kWh by the time you reach dashboard zero (plus or minus cheating using energy from that buffer for dashboard smoothing due to recalibration). That’d be 5-8% for Model 3s. Throw in anti-brick, if that’s a few % too, then if top buffer really is near zero, we are looking at true SoC being, ya, about 55% at dashboard 50% . Like you said. 54.5-56%.

Hmmmmm .... do you have enough resolution in your SC profile charts for 3 LR vs SR to correlate the two SoC’s with each other? Thought being they’d taper at a “true X%” on each model, which may give hints as to some of these numbers if e.g. the LR chart looked shifted vs the SR chart by 1-2%?

Of course, check the Tesla parts catalog. Both drive units have an oil to coolant heat exchanger being fed by coolant from/to the Superbottle.

I continue to wonder about that front induction motor’s contribution to the battery heating. IIRC, the stator in the PM motor takes the brunt of the heat losses and the rotor stays cooler, I’m unfamiliar with where all the oil is in the electric motor, but just from this one detail I had imagined the heat from the “easier to access” (in my mind) outer stator from the rear motor to be more easily harnessed for useful purposes than the front induction motor who, again IIRC, would have cooler stator but warmer rotor (vs rear PM switched reluctance motor). If anything, the hotter rear stator might be better at transferring waste heat to the coolant? In any case, the rear motor for sure has the ability to be forced to generate waste heat somewhat “efficiently” due to its electrical design vs the inductance motor, regardless of which parts get how hot. We probably need people sniffing CAN bus packets on a dyno to know the answer
Wugz on reddit has already given great info that you linked to. Maybe jwardell will use his ‘back to the future rig’ to provide more info. I recall he posted a response on that reddit thread.

 

[EV-Tech Exp]

Model 3 battery heating (ignoring the cabin heater) appears to be either 4 or 7 kW based on u/Wugz data on reddit: On-Route Battery Warmup Measured : teslamotors. The front motor sounds distinctively different when ORBW is in use, so I expect it is contributing in some fashion to the heating process.

Fantastic info - has anybody done a similar test with a RWD vehicle?

 

[EV-Tech Exp]

This is very interesting data. Do you have any reason to think the Panasonic/Tesla 2170 NCA cells perform differently than the 18650 cells in this study?

Based on this, it seems storage below 55% actual SoC is desirable. That translates to about 50% indicated SoC.

In terms of effect of storage SoC, I'd expect the Panasonic/Tesla cell to have similar behaviour in principle, however I'd expect the capacity loss to be somewhat less. Cells used in the automotive space will typically contain additional electrolyte additives to help provide longer term stability. I suspect the academic paper has deliberately chosen a cell which degrades reasonably quickly to attain meaningful results in 10 months.

 

[Zoomit]

Hmm, you really think they let us go to true 100? I haven’t read anything about this that I recall. I was guessing no.
I was guessing (b) was that infamous 4 kWh “energy buffer” and my theory on that is that it gets built up from 0 kWh at 100% SoC to ~4 kWh by the time you reach dashboard zero (plus or minus cheating using energy from that buffer for dashboard smoothing due to recalibration). That’d be 5-8% for Model 3s. Throw in anti-brick, if that’s a few % too, then if top buffer really is near zero, we are looking at true SoC being, ya, about 55% at dashboard 50% . Like you said. 54.5-56%.

Hmmmmm .... do you have enough resolution in your SC profile charts for 3 LR vs SR to correlate the two SoC’s with each other? Thought being they’d taper at a “true X%” on each model, which may give hints as to some of these numbers if e.g. the LR chart looked shifted vs the SR chart by 1-2%?

Well, you went ahead an over-thought it! I'm really not sure how the percentages play out. As I said, I was rounding to the nearest 5%. 55% actual SoC is more than 45% indicated SoC and obviously less than 55% indicated SoC.

Fantastic info - has anybody done a similar test with a RWD vehicle?

I have not seen any similar reports with a RWD.

 

[Jedi2155]

I absolutely love you video on battery degradation mechanics from the electro-chemical perspective. I've spoken for various battery engineers/researchers on the subject but I've never seen such a detailed and succinct summary of degradation as yourself.

Question regarding degradation at 100% SOC. I've done a number of charges to 100% SoC for several reasons but I'm concerned about harming my battery unnecessarily. The reasons for doing so include

• Getting an accurate capacity measurement
• Provide an opportunity for the BMS balance the pack where module voltages show its greatest deltaV
• Occasionally because the energy was free and I needed to avoid an idle fee....(fewer times than digits on my hand =))

I've heard that charging to 100% even once might have significant negative impact but I'm not entirely sure why. Previously, I was under the impression the danger was not getting to 100%, but rather long duration storage at 100%. From your video, however it sounds like lithium plating and mechanical stress at very high SOC are additional concerns beyond increased rates of electrolyte decomposition (my historical understanding) so I should really avoid charging to 100% if I can avoid it (of the dozen or so times I've done it I only really needed it once). Would that be your advice or do think I'm overly worried about 100% SOC?

There are some very thoughtful and interesting questions in this thread!
2. I'm not sure what Tesla does on this, however I would expect them to circulate coolant when the battery is becoming excessively hot, i.e. >50°C. They do however need to balance this with the customer expectation that the vehicle does not consume excessive power when sat unused. A fine balance needs to be struck. Maybe those who live in hotter climates can help us understand what their vehicle does?

Although I don't have hard numbers on the subject, I can comment living in Southern California that I definitely hear my vehicle cycle pumps/coolant when the ambient temperature is especially high (>85-90F) hours after I've parked the vehicle.

Thanks for the great educational video!

Got a couple of questions for you -

1. What rate is considered "Fast charge"? I don't have a Tesla yet, but can't stop consuming as much information as I can get my hands on. A friend of mine who just got an M3 ran a cable from his stove and is getting 52Km/hour as his charge rate - this would be from a Nema 14-50 plug (see attached screen shot)
2. How long does it take typically to pre-condition a battery (and what ambient temperature would that be)?

I think there is important point to be made that "Fast Charge" by SAE definition is clearly defined from some earlier charts. To a battery however, "fast charging" is really a function of its capacity. Charging a 24 kWh pack at 50 kW (~2C) is REALLY fast charging. Charging a 100 kWH pack at 50 kW is not really that bad (0.5C). From my perspective, a charge rate at or faster than a 1 hour charge time is considered fast charging to the battery perspective.

 

[KootsChewt]

Completely correct that lithium plating would have more of an impact - at these very low temperatures, storage at 90% SoC will have minimal negative impact in terms of electrolyte decomposition and undesired parasitic side reactions, however invoking additional lithium plating could have a significant impact.

Well that's very interesting! I was already doing most of the recommendations in this thread, but this one is new to me. I live somewhere it is below freezing for months at a time. What temperature does the plating start to become more significant? I'll have to change my current charging regime for winter months (I currently have a timer delay so the car sits as little as possible above 80%).

Anecdotally, I should add that my first EV is a Leaf. For the first 4.5 years it was my daily driver, and due to the charging limitations, I couldn't set it to stop at 90% (or any other value). So I used delay charging to have it reach 100% just before I left for work, then charged at work to 100% again before driving home. Once I got the Model 3, the Leaf has now had several months of minimal daily driving, but it often sits at 100% for upwards of 12 hours. It is degrading at a similar rate now driving only 7,500 km/yr as it was at >35,000 km/yr!

 

[jdw]

On the subject of Lithium plating when charging a cold battery, does anyone know what happens when connected to shore power running the battery & cabin heaters? As far as I can tell, the battery, on one hand, isn't charging, but either (a) the current from shore power must be flowing through it (?) or (b) the inverter is powering the heaters directly, bypassing the battery?

I usually warm the battery using shore power in the winter, but if all power flows through the battery, that may not be the best plan ...

Anyone?

 

[ReddyLeaf]

......Once I got the Model 3, the Leaf has now had several months of minimal daily driving, but it often sits at 100% for upwards of 12 hours. It is degrading at a similar rate now driving only 7,500 km/yr as it was at >35,000 km/yr!

Well, stop doing that! Leave the Leaf at 4-6 bars charge for in-town driving.