Cold weather, Range & the Battery

[evnow]

Here is a question for people with Li battery experience.

How & why does the cold affect the battery. We know from various accounts that the range gets reduced quite a bit in cold weather. But why ?

From some web searches I did yesterday I see that
- In severe cold battery can get damaged
- The cold decreases the chemical reaction within the battery reducing current
- It becomes more difficult for the BMS to figure out the SOC in cold weather
- As we all know heating will take away some energy in cold weather

Corollary to the question is - how does a liquid colled/heated battery (as in Volt/Focus) help in this situation ? Does it just prevent damage or will it make the capacity reduction less. We have seen reports of low range for Volt in cold weather.

 

[DaveinOlyWA]

daniel at PC outfitted his Zebra with Li a few years back. he lives in Spokane and claims no noticeable loss of range.

i had lead acid in my Zenn and it was about 15-25 % range reduction but part of that was simply water on the road. in a car that can only do 38 mph max, any drag affects its speed so i did notice in heavy rain or where standing water on the road made a difference, i was lucky to get up to 33-34 mph

 

[UhClem]

- The cold decreases the chemical reaction within the battery reducing current

This implies we may see a loss of performance in cold weather besides a loss of range. I'm wondering if we will see this with the Leaf and at what temperatures?

 

[EVDRIVER]

- The cold decreases the chemical reaction within the battery reducing current

This implies we may see a loss of performance in cold weather besides a loss of range. I'm wondering if we will see this with the Leaf and at what temperatures?

Floor it, the current will warm the pack

 

[UhClem]

Floor it, the current will warm the pack

Sorry Officer, I was just getting my pack up to optimum operating temp

 

[AndyH]

It's a combination of factors.

The Leaf won't let us use the car or charge the pack when the pack is too hot or too cold, so we don't have to worry about those extremes.

A cell's internal resistance increases when the cell is cold. Cells with lower internal resistance release energy quicker and do it with less internal heating. In a cold cell with higher internal resistance, some of the energy when charging or discharging is converted to heat - which eventually reduces internal resistance and reduces heating.

In addition, cold air is more dense - so speed and aerodynamics have more effect in the winter.

And yes - cabin heating loads increase, shorter days means more use of lights, etc.

The BMS works by measuring cell voltages - and that process is not negatively affected by cold. Absolute zero maybe, but -20F? Fugeddaboudit!

 

[sjfotos]

It's a combination of factors.

The Leaf won't let us use the car or charge the pack when the pack is too hot or too cold, so we don't have to worry about those extremes.

A cell's internal resistance increases when the cell is cold. Cells with lower internal resistance release energy quicker and do it with less internal heating. In a cold cell with higher internal resistance, some of the energy when charging or discharging is converted to heat - which eventually reduces internal resistance and reduces heating.

In addition, cold air is more dense - so speed and aerodynamics have more effect in the winter.

And yes - cabin heating loads increase, shorter days means more use of lights, etc.

The BMS works by measuring cell voltages - and that process is not negatively affected by cold. Absolute zero maybe, but -20F? Fugeddaboudit!

Hello Andy.
Your posts are always informative, thank you. I saw some earlier commentary from Nissan in the Owner's Manual that cautioned about operating the car in temperatures below about -15 degrees (as I remember it) Fahrenheit. Certainly conditions that would be encountered on a regular basis in Minnesota where I used to live. I wondered if this was a limitation of the chemistry involved. but maybe not.....in any case, it will be interesting to see what they plan to try and do with the Cold Weather Package to mitigate this.

 

[lne937s]

It's a combination of factors.

The Leaf won't let us use the car or charge the pack when the pack is too hot or too cold, so we don't have to worry about those extremes.

A cell's internal resistance increases when the cell is cold. Cells with lower internal resistance release energy quicker and do it with less internal heating. In a cold cell with higher internal resistance, some of the energy when charging or discharging is converted to heat - which eventually reduces internal resistance and reduces heating.

In addition, cold air is more dense - so speed and aerodynamics have more effect in the winter.

And yes - cabin heating loads increase, shorter days means more use of lights, etc.

The BMS works by measuring cell voltages - and that process is not negatively affected by cold. Absolute zero maybe, but -20F? Fugeddaboudit!

Resistance goes down the lower you go in temperature, and goes up as you increase temperature (think superconductors in liquid nitrogen). However, chemical reactions also slow down as temperature goes down and speed up as temperature goes up. As batteries store electricity chemically, you don’t want the temperature to go down too low as it slows the chemical reaction that releases electricity. You also don’t want the temperature to go up too high as it increases resistance, which loses energy, increasing heat… eventually leading to failure of the battery.

 

[Smidge204]

Resistance goes down the lower you go in temperature, and goes up as you increase temperature (think superconductors in liquid nitrogen). However, chemical reactions also slow down as temperature goes down and speed up as temperature goes up. As batteries store electricity chemically, you don’t want the temperature to go down too low as it slows the chemical reaction that releases electricity. You also don’t want the temperature to go up too high as it increases resistance, which loses energy, increasing heat… eventually leading to failure of the battery.

With the materials in question, the temperature ranges see during even extreme conditions are a non-issue as far as electrical resistance is concerned.

Cold slows chemical reactions, as you said. Heat causes the electrolyte to degrade, which at best makes it harder for the ions to travel and reduces power output. After that it coats the electrodes with nasty gunk causing permanent capacity and power degradation. If things get really bad, the gas pressure from the degrading electrolyte pops a safety valve and the battery is completely dead after that.
=Smidge=

 

[AndyH]

It's a combination of factors.

The Leaf won't let us use the car or charge the pack when the pack is too hot or too cold, so we don't have to worry about those extremes.

A cell's internal resistance increases when the cell is cold. Cells with lower internal resistance release energy quicker and do it with less internal heating. In a cold cell with higher internal resistance, some of the energy when charging or discharging is converted to heat - which eventually reduces internal resistance and reduces heating.

In addition, cold air is more dense - so speed and aerodynamics have more effect in the winter.

And yes - cabin heating loads increase, shorter days means more use of lights, etc.

The BMS works by measuring cell voltages - and that process is not negatively affected by cold. Absolute zero maybe, but -20F? Fugeddaboudit!

Resistance goes down the lower you go in temperature, and goes up as you increase temperature (think superconductors in liquid nitrogen). However, chemical reactions also slow down as temperature goes down and speed up as temperature goes up. As batteries store electricity chemically, you don’t want the temperature to go down too low as it slows the chemical reaction that releases electricity. You also don’t want the temperature to go up too high as it increases resistance, which loses energy, increasing heat… eventually leading to failure of the battery.

Yes - you're spot on from a single factor - resistance of a copper plate at different temperatures. And what you describe from the chemistry side sounds reasonable as well. I think, though, that we'll hit the ~65°C point where the electrolyte starts to break down before we're worried about high heat increasing resistance.

I'm a technician - I test and group cells and sell packs but don't design cells. What I know comes from the engineers that design the LiFePO4 cells I import. There's a great video from Carnegie Mellon here in the battery section that beautifully covers cell guts and the 'equivalent circuit' of resistance and capacitance used to model cell behavior.

Internal resistance is a very easy test that gives a very good indication of cell health. Damaged cells have higher internal resistance in all conditions than a healthy cell, for example. That's one of the reasons that Nissan's BMS not only monitors temperatures, voltages, and current but monitors internal resistance as well.

LiFePO4 is affected more by cold than LiMn2O4. But I don't have charts on the Leaf cells...so we can get a general idea from what is available...

This info is for a nominal 11Ah LiFePO4 cell undergoing the same constant current discharge at three different temperatures.

The 25°C cell has low (normal!) internal resistance and less energy is lost to heat. Less loss means higher cell voltage under load and highest capacity - so better speed and/or longest range.
The 0°C cell has higher internal resistance - more energy is wasted as heat and is not available to move the car. We get more voltage sag and less range.

The same thing happens during charging - it's a bit slower in the winter because some of the energy from the charger is converted to heat. The effect tapers off as the cell warms and internal resistance drops. If we need to get the quickest recharge to get the car back on the road, put the car on the charger as soon as possible after the drive as the pack will be warmer from working.

Don't try to equate this info directly to Leaf range as our LiMn2O4 cells are better in the cold than these demo 5+ year old LiFePO4 cells.

I hope that's useful,
Andy

edit...
you nailed it, Smidge!
Steve - thanks very much!

 

[rmay635703]

Maybe I missed it but the most significant reason for range loss in cold is usually because of stiff tires (high rolling resistance), stiff grease in all portions of the car and drivetrain and obviously white stuff massively increases rolling resistance..

 

[DaveinOlyWA]

Maybe I missed it but the most significant reason for range loss in cold is usually because of stiff tires (high rolling resistance), stiff grease in all portions of the car and drivetrain and obviously white stuff massively increases rolling resistance..

biggest reason is the same as being in very hot summers; climate control.

when i flip on the defrost, my range estimates drop 15 miles. that will be the same come summer although i am pretty sure the A/C hit is not as severe.

the other (much lesser) reason is resistance. cold air is denser so its harder to push when driving down the road.

rolling resistance also plays a smaller part but only because snow and rain creates drag and lowers performance as well.

 

[Train]

I agree. I'm thinking the climate control system will require a significant portion of current draw. Be it A/C in the summer and heat in the winter.

 

[DaveinOlyWA]

well its a question of logistics. in one scenario like today when losing 15 miles of range. it was 38º out and i had temp set to 72º that is 34º temp difference.

now, its easier to cool air than to warm it and we have some pretty efficient A/C units and most cool air from the say 90's or cooler to the 70's so only a 20º some odd degree drop.

so i would guess in summer, the range drop would be less.

 

[garygid]

Haven't we been told that a very cold battery will hold (or deliver) substantially less energy?

 

[AndyH]

Maybe I missed it but the most significant reason for range loss in cold is usually because of stiff tires (high rolling resistance), stiff grease in all portions of the car and drivetrain and obviously white stuff massively increases rolling resistance..

This may help a bit. This is an energy loss chart for a typical internal combustion engine powered car/light truck:

Each of the numbers in the white boxes is how much energy that system uses.

With regard to differences in hot/cold for these items, note that the transmission only accounts for 1.5% of energy loss overall. Wheel bearings are covered by "axle" for another 1.5%. The Leaf does have a 'transmission-like-object' with its single speed gear reduction and differential unit. The Leaf uses synthetic automatic transmission fluid (ATF) in the gearbox - and ATF is a very low viscosity fluid - very close to the viscosity of 0W-20 engine oil. Drivetrain losses are very low in the Leaf - winter or summer.

Note that aerodynamic drag has twice the impact as transmission/axle losses - and cold, more dense winter air is harder to push thru than less dense summer air.

For the rest - check out Evnow's post over here: http://www.mynissanleaf.com/viewtopic.php?f=8&t=2464 where he links to new info on climate control and EVs.

...We found that climate control loads can reduce...range by 35%...

 

[Smidge204]

Maybe I missed it but the most significant reason for range loss in cold is usually because of stiff tires (high rolling resistance)

Stiff tires would be a great improvement for rolling resistance.: Less deformation means less energy wasted. Sadly temps don't get that low outside of Antarctica That does happen, though, is cold weather decreases tire pressure a bit - that makes the tires softer, increasing rolling resistance.

"Stiff grease" is generally not a problem either, and if really got that stiff friction would heat it up so fast as to not make any difference.
=Smidge=

 

[mwalsh]

This is fairly anecdotal stuff, so take it for what it's worth, but when it was colder on Monday morning I got 6.5 miles per SOC bar for the first 4 bars of my commute. This morning it was warmer and I got the 7.5 miles I'm used to seeing. Actually I got here without dipping into bar 4 at all, so better than 7.5 miles. The drives were not massively different, but then it's very hard to faithfully replicate precise circumstances from one drive to another.

 

[Carcus]

The biggest day to day changes in efficiency (assuming I'm driving in a consistent fashion):

1. Temperature (dense air causing extra drag)
2. Winds (anything more than about 45 deg off the tail will hurt efficiency -- i.e. winds hurt more than they help)
3. Traffic

These factors are prioritized in order, but they can change places depending on the day. For me, in a relatively windy area, wind will often be the biggest detractor.

/data comes from obsessing over a scangauge in a F150 pickup.

But, ....

I've also watch my 3 series BMW fairly closely, and on that car I would prioritize:

1. Traffic
2. Temperature
3. Winds

Being pretty low slung, the drag factors don't seem to effect it's mpg near as much. But I suspect it's got a fairly "thirsty" idle. The mpg will nose dive if it has to sit in traffic/ at a lot of stop lights.