any permanent battery degradation driving in extreme cold?

[AAKEE]

This is a chart from a lithium plating research report.
At 1C, we need a battery temp of 25C to avoid lithium plating (do nor remember the chemistry but it do not seem to differ very much between chemistries.

The battery heating probably heat the battery enough for slow AC charging.

 

[Regaj]

To provide some additional context for the chart @AAKEE posted, here are some approximations of how different DC Fast Charging speeds relate to C-rate (these are based upon the nominal 82.1 kWh pack in my dual-motor Model 3):

250 kW = 2.77 C-rate
150 kW = 1.83 C-rate
100 kW = 1.22 C-rate
50 kW = 0.60 C-rate

As can be seen, the 1.0 C-rate explored in @AAKEE 's chart happens at a very modest Supercharging speed.

L2 AC charging is much, much less likely to expose your battery to the risk of Lithium plating. But if it gets cold enough, even L2 charging is a problem.

 

[ay221]

If I leave my AC 240v/40amp charger hooked up when it's below freezing, Tesla will warm up the battery first and then charge up or must I select departure time for that to happen? Thanks.

 

[AAKEE]

L2 AC charging is much, much less likely to expose your battery to the risk of Lithium plating. But if it gets cold enough, even L2 charging is a problem.

Good post, but I do not really agree on the L2 thing (if I understand the term L2 correct).

L2 = AC-charging so for 3/Y = max 11kW?
So thats about 0.13C or so.

Tesla do not charge the battery if it is to cold (sub freezing, with a margin) Even if connected at 11 kW and the battery is cold the charging power is very modest until the battery is heated. I would not worry about that, and Im quite sure

Regen has been quite high before at low battery temp, when seeing below 10C cell temp I have not been releasing the accelerator completely, and have been using my Scan My Tesla screen to manually keep in low.
I think Tesla came to the same conclusion because this summer they reduced the regen so it is much mire limited by battery temp.

+5C is quite safe even up to 1C.

Tesla barely charge at all until the battery temp is +3C and when charging with 2-3 kW (0.03C or so) the batt temp is kept at 8.75C.

Charging with the UMC right now at work with 10A/230V so 2.3kW.
Arrived with 13.3C cell temp, Ill check the batt temp when it has stabilised. Its around -10C outside.

 

[Regaj]

Roger that, @AAKEE. I agree that L2 charging is rarely a problem. I was speaking of the most extreme conditions... the "bomb cyclone" spreading across most of North America right this moment certainly brings EV charging into sharp focus for a lot of us.

I'm not aware of any good studies that explore Lithium plating at what usually would be considered very low C-rates, at extremely low temperatures. But what research does exist suggests there may be a lower bound beyond which any charging is a risk. I think that's more a theoretical situation than a real one. But it does beg the question.

The good news is that if one can avoid Lithium plating, cold weather is generally pretty kind to EV battery packs!

 

[KenC]

Thanks to everyone who replied, @cwerdna , @AAKEE , and @Regaj!

Anyhow, in conclusion, I was trying to understand what was actionable for us owners. What would be best practices? Is there anything we can do besides pre-conditioning?

Aakee thinks Tesla's BMS is going to heat the battery and mitigate the worst possibilities, and according to the UAF article, the worst possibilities, dendritic growth is an extreme result, "In extreme cases, lithium plating can take the form of dendrites" I would hope Tesla's BMS can prevent that, right? But preventing the source of dendritic growth, ie permanent lithium plating, would seem to be a good approach.

So, will Tesla's BMS protect us against permanent plating or is there something we need to do and when do we need to do it?

Regaj was kind enough to pull from the UAF article what seems as actionable:
● Under 10°C (50°F): Lithium plating and permanent degradation can occur with fast charging below this temperature.
● Under 0°C (32°F): This is the recommended lowest temperature for normal use of standard Li-ion batteries. Below this temperature, anything faster than Level 1 charging may cause lithium plating degradation.
● Under -20°C (-4°F): In addition to significantly reduced charging and discharging power capabilities, the recommended storage range (no active charge or discharge) is generally down to about -20°C (-4°F) for standard Li ion batteries used in EVs. The battery may not survive prolonged temperatures below this threshold.

I'm assuming the temps are Pack temps, not ambient temps, so without that info, we're still wondering what to do.

Since, as Regaj notes, it would be a great "feature" if Tesla gave us the average pack temp, what does the BMS do under cold conditions? When it's cold and the car is plugged in, how warm does that keep the pack? Presumably above 32F so I can use my L2 charger? I did look at SMT once, and noted that it showed my battery cells at 42F, but that was just on my routine commute. I wasn't supercharging. Having said that, I've driven off to go skiing, and not pre-conditioned or anything, and supercharged, rather slowly. In hindsight that sounds like a bad approach.

Thanks to the chart aakee posted, we need a temp of 25C or about 77F for the pack to charge at 1C rates, which seems to be about 80kW for a normal sized Model 3 battery. Shouldn't the Tesla BMS be managing this? Since we can't control supercharging rates, and as Regaj notes, Tesla's interest is in supercharger efficiency in getting cars in and out, what can we do, other than be sure to pre-condition on our way to the charger? Should we be trying to charge at higher SOCs, ie above 50% SOC, so that we are lower on the charge curve, ie charging at a slower rate, below 1C?

Anyway, lots of food for thought, and I think I'll change some of my charge habits when I go skiing and have to supercharge on the way!

 

[AAKEE]

Roger that, @AAKEE. I agree that L2 charging is rarely a problem. I was speaking of the most extreme conditions... the "bomb cyclone" spreading across most of North America right this moment certainly brings EV charging into sharp focus for a lot of us.

I'm not aware of any good studies that explore Lithium plating at what usually would be considered very low C-rates, at extremely low temperatures.

I am!

The concensus is that at (very) low C-rates you can charge at subfreezing levels.

As you did wrote earlier, the lithium ions move slow at low temperature and if you send to many of these they stack up in the que and cause blobs of lithium.
If you keep the charging rate small enough to the ability to move, the can handle it and dont stuck up in blobs.

Here’s one example:
https://mdpi-res.com/d_attachment/b...loy/batteries-08-00206.pdf?version=1667368670

These NMC Pouch cells (if I remember it right) was cycled at -10C

Cell 1-1 and 2-1 was charged at 0.1C and actually did not decrease in capacity at all.
0.2/0.3C did cause slightly lithium plating and above severe.

The good news is that if one can avoid Lithium plating, cold weather is generally pretty kind to EV battery packs!

Yep!

 

[AAKEE]

Thanks to everyone who replied, @cwerdna , @AAKEE , and @Regaj!



I'm assuming the temps are Pack temps, not ambient temps, so without that info, we're still wondering what to do.

Since, as Regaj notes, it would be a great "feature" if Tesla gave us the average pack temp, what does the BMS do under cold conditions? When it's cold and the car is plugged in, how warm does that keep the pack?

Plugged in but not charging = I would say it does not keep the battery at an elevated temp.
My car is always plugged in at home but at a heated garage.
At my mother in law, I charge to a set level and mostly do not disconnect when the charging is done. When the ambient is well below freezing, the cell temp enter freezing levels eventually.

I am not at home right now, so I do not think I have the data available but I have logs showing [BMS_max charge power] related to battery temp.
From memory it is about zero to about +3C and than it climbs rather quick with increasing temps.
If the only parameter for max AC charging was “save the battery” but Tesla also would increase the charging time quite much if they did.
The hunt for very fast charging is not only impatient Tesla owners, the shorter the charging time the less charging stalls is needed. So they need to compromise between fast charges and the battery “taking an hit”.
I always preheat because I have seen that they allow quite fast charging at low battery temp. Of course Tesla know this, they balance it to acceptable levels.

Shouldn't the Tesla BMS be managing this? Since we can't control supercharging rates, and as Regaj notes, Tesla's interest is in supercharger efficiency in getting cars in and out, what can we do, other than be sure to pre-condition on our way to the charger? Should we be trying to charge at higher SOCs, ie above 50% SOC, so that we are lower on the charge curve, ie charging at a slower rate, below 1C?

I have a slight memory that there are regions higher up in SOC that cause lithium plating so stsying high is most probably not going to help.

The research on fast charging shows that when the cell temp is 40C or above, lithium plating do not occur at 4-5C.

Tesla has another reason to preheat more, shorter charging times. A complete preheat is 48C for my M3P 2021.
Preheating increases the batt temp with about 1C / minute up to 40C, after that its slower…ramping up to 48C.
The target at Supercharging session is about 58C

So, preheat and use Supercharger just as usual, it is quite safe.

I have some 50+ Supercharging sessions, 56k km (35 k mi) and have very little range loss. Saw 496 km at 99% today out of 507km.
Preheated supercharging is not what degrades a M3 or Y battery.
Nor is charging full.
Time at high SOC is, specially in hot climate.

Anyway, lots of food for thought, and I think I'll change some of my charge habits when I go skiing and have to supercharge on the way!

If you can preheat, dont be afraid to supercharge.

I have my car parked for a week at the time at work outside, getting cold. There is no Supercharger nearby but another 200kW DC charger. I did go to a 25kW DC charger twice, letting the battery warmer heat the battery (use like half of these 25 kW) abd afyer reaching 45C I have driven the 3 km to the 200kW charger and continued there.
This because Im not happy to see 130kW on a cold battery. If it can be avoided…

 

[AAKEE]

So I drove to work at -20C

Here at work currently -14C, and the car is charging since arrival 12hours ago. Charging single phase 10A/230V = 2.3kWh.

At arrival the battery was 13.3C.

The charging changes between charging with 2kW and 1 kW so repeatedly the battery heat is running to keep the battery at the by Tesla /BMS desired level.

The battery temperature is 9.25C, regulated to stay there.
Inlet power 2.3kW - car awake (~0.2kW) so there is about 2.1 kW to use.
12hrs times 2.1 = 25kWh and the car reports +19 kWh. About 25% has been used to keep the battery warm.




If this charge had been started with the battery cold, the battery had been heated before the charging started.

 

[ay221]

I will use plan departure for winter so the battery warms up first.

 

[Regaj]

<<.
Here’s one example:
https://mdpi-res.com/d_attachment/b...loy/batteries-08-00206.pdf?version=1667368670 >>

Thanks for posting this report, @AAKEE. It is excellent!

Yes, as far as actionable items, making sure the battery is warmed before driving or charging is about all we can (or need) to do. Unfortunately, Tesla doesn't provide any native tools to gain insight into pack temperature - which is the critical thing we're worried about. Scan My Tesla solves that, but it's too bad we need to go to a third-party app to get such crucial information.

Like @AAKEE, I've not observed a plugged-in car automatically keeping the pack warm. I expect it might when it gets really cold - last week I observed the "Target Bat Active Heat" at 19.0F (-7C), when ambient temps were in the 30's (Fahrenheit). But it doesn't actively heat the pack at those winter temps most of us see, most of the time. Turning Climate on will warm the pack if it is cold enough.

The other thing to bear in mind is that there is a significant lag (from ambient) when heating or cooling the pack. Tesla's implementation of pack heating by sending power to the stators, which then heats the coolant, which then circulates among the pack cells... is something I'd call clever. But it's not especially efficient and it's not especially fast. A very cold pack takes some time to warm.

So give it plenty of time.

 

[AAKEE]

Like @AAKEE, I've not observed a plugged-in car automatically keeping the pack warm. I expect it might when it gets really cold - last week I observed the "Target Bat Active Heat" at 19.0F (-7C), when ambient temps were in the 30's (Fahrenheit). But it doesn't actively heat the pack at those winter temps most of us see, most of the time. Turning Climate on will warm the pack if it is cold enough.

I’m at work, the car is parked outside until tuesday noon.
I did charge up to 60% after arrival with the UMC at 2.3kW single phase 10A/230V.
The pack was hold at 9C during the charge by battery heating.

Now it is 14 hours since the charge was finished and the battery temp was -4.25C when I check a while ago. The car is still connected.
The car has been sleeping so more or less certain no battery heat has been used.
I will let the battery cool down, today it is only -12C nice and warm but it will get a little colder the coming days.

I have to wake the car to see the batt temp.

 

[Braumin]

Yes, as far as actionable items, making sure the battery is warmed before driving or charging is about all we can (or need) to do. Unfortunately, Tesla doesn't provide any native tools to gain insight into pack temperature - which is the critical thing we're worried about. Scan My Tesla solves that, but it's too bad we need to go to a third-party app to get such crucial information.

They don't provide this info to the end user because the car takes care of this itself. If the pack is cold, output power is reduced, sometimes significantly, and there is no regen until the pack warms up.

If you are concerned about this, yes, precondition before you go. That's what it is there for. The car is designed to work in the winter. It handles everything on its own. It won't let the user hurt it.

Sure, I would love an advanced screen that shows me more data. I think we all love more data. But, we are in the minority. Most people don't want more data because the data with no knowledge of what it means is just confusing.

 

[AAKEE]

Update to the post above.

-9 Outside.
20 hours since the charge finished.
Car still connected.
Batt temp -9.00
No battery heat has been used.
The car has been sleeping except woken up by me to see the cell temp.

 

[Rocky_H]

But what research does exist suggests there may be a lower bound beyond which any charging is a risk. I think that's more a theoretical situation than a real one.

That's definitely real and not hypothetical. Plenty of us have seen that state in our cars, where we tell it to charge, and it just sits there sucking energy from the wall and funneling it into the battery heater but doing NO charging yet, because it has to warm it up some to near freezing before it will begin any charging.

I saw the bar chart @AAKEE showed earlier where it's presenting a fixed charge rate and then at what temperatures there is the plating damage. But you can also look at that from a different end:
For a given temperature, where is that threshold of how much power it can take while staying safe below the plating point? It's a sliding scale, so for some level around freezing or below, any charging damages it. At some point, you can safely start trickling in a little. And as the temperature keeps going up, it can safely increase the power while staying below the plating point. (And no, I'm not going to go try to find charts of it to give specific numbers. That would vary too much based on battery chemistries, but it's the general principle.)

 

[AAKEE]

For a given temperature, where is that threshold of how much power it can take while staying safe below the plating point? It's a sliding scale, so for some level around freezing or below, any charging damages it.

Yes, below 0C / freezing the lithium ions can not move fast so almost any charging causes lithium plating.

There are some lithium batteries (other chemistries) that can be charged sub freezing, but our lithium batteries in the cars can not.

 

[Rocky_H]

My Zero electric motorcycle doesn't have any way to heat the battery, so I've seen it just sit plugged in and not charge until it sits in the garage long enough to warm up from ambient air to get warm enough to begin charging. Good for it that it's preventing damage though.

 

[AAKEE]

Quite obvious that they do not like sub zero. 1C is quite high charging power, but still…

I’ll try to find the research report from which I took the picture @Rocky_H refered to.