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I've never accepted the prevailing misconception that active thermal management is beneficial to BEVs, when driven in all but the most extreme climate conditions.

This would seem to be because BEV owners remain largely oblivious to the drawbacks of ATM, not the least of which is the diversion of traction energy to pack thermal management, and the resulting loss of efficiency and range.

I believe that is the primary explanation for what we see in the results below.

The AAA published what looks to be a valid study of five USA market BEVs, which attempts to quantify the loss of range when driven in extreme ambient temperatures.

The general statement below, from page 50, is followed by several charts showing the superior performance of the passively managed LEAF (less loss of range and efficiency) in extreme temperatures.

I also expect the LEAF's out-performance of the other packs at 95 F would show up far more significantly in tests conducted at even higher temperatures, as the energy required to cool a battery pack increases dramatically at higher ambient temperatures.

95 F (~35 C) is really only a warm day, not a hot one, here in North California.

"Summary of Test Results

For tests conducted at 20°F and 95°F, HVAC use resulted in significant reductions in driving range and equivalent fuel economy. For all test vehicles, it was observed that the UDDS drive cycle was most affected in terms of increased energy consumption, reduced driving range and reduced MPGe. This consequently resulted in reductions of combined driving range and combined MPGe values as previously discussed in Section 5.3. Compared to 75°F, HVAC use at 20°F resulted in an average reduction of combined driving range and combined MPGe by 41 percent and 39 percent, respectively. HVAC use at 95°F resulted in an average reduction of combined driving range and combined MPGe by 17 percent and 18 percent, respectively.Figures 51-52 illustrate the percent change of combined driving range and combined MPGe values relative to testing conducted at an ambient temperature of 75°F..."


E.1. Research Report EV Range Testing FINAL 1-9-19 | Lithium Ion Battery | Electric Vehicle
 

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LEAF is a joke for distance travel in high temperatures, even the first rapid of the day is limited speed due to heating in the current model.

It also destroys its packs, with degradation at perhaps 4x the speed experienced by other makes.

HVAC use is not at all like pack thermal management so the document you link is of little relevance to your bizarre theory. Much of the pack's need for high-power thermal management is met from the mains while still connected - either pre-heat in the cold before departure, or high-power cooling while rapid charging. The pack tolerates a much wider range of temperatures than cabin occupants do, and in modern designs is passively warmed by waste heat from the drivetrain, and cooled by circulation of air or water without the need for a chiller, avoiding a great deal of the energy expenditure which HVAC incurs.

It is interesting that everyone except Nissan has battery thermal management. Clearly you're right and they're all wrong.
 

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I've never accepted the prevailing misconception that active thermal management is beneficial to BEVs, when driven in all but the most extreme climate conditions.

This would seem to be because BEV owners remain largely oblivious to the drawbacks of ATM, not the least of which is the diversion of traction energy to pack thermal management, and the resulting loss of efficiency and range.
Your whole post is based on an incorrect premise.

Battery thermal management isn't about increasing range, although it can make a small improvement to range under extremely cold conditions where the battery cell resistance would be quite high and the extra energy expended initially heating the battery is offset by the improved battery efficiency for the remainder of the trip. Only applies to a long trip however otherwise the "departure tax" of heating the battery is a net loss, unless it is done while still plugged in.

Battery thermal management is all about about protecting the battery to minimise it's degradation with time and mileage, and also to maximise rapid charging speeds.

If a battery is too cold it can't be charged very fast otherwise dendrites would be formed that eventually short the cells out. Having the cells short out and catch fire burning the car down is not a good result so all BMS systems severely limit rapid charging speeds at low temperatures to avoid this dangerous situation.

A battery heater allows the battery to be warmed up into the region where it can charge faster, so you can choose to trade some at the wall energy efficiency for faster charging times - which might be valuable on a long trip where you want to rapid charge and move on as soon as possible and don't care that it might cost you an extra 10% energy to heat the battery.

At VERY low temperatures (something like -20C and below) it becomes impossible to charge the battery AT ALL. So in these very cold conditions a battery heater is absolutely essential to warm up the battery before charging can even commence, and the energy loss using it is just part of doing business in very cold climates like Canada or Scandinavia. (Although this "wasted" energy comes from the charger, so doesn't reduce range, it only increases at the wall consumption)

Funnily enough, even the Nissan Leaf has a battery heater in these markets. I wonder why.... ;)

At the other end, a hot battery (>35C) whilst being able to charge quickly suffers much greater degradation over time. If you let the cells get up to 50C or more while charging - as the Leaf 2 does, cell life will be greatly curtailed, and charging speeds have to be severely limited to keep the temperature from getting any higher.

A car that can rapid charge and keep the cells at say 35C whilst still charging at full speed will not only charge faster but have far less battery degradation over time than the one that lets the cells get to 50C or more. Also un-cooled or basic fan air cooled packs allow the cell temperatures to diverge dramatically under heavy charge and discharge, (I've seen as much as 10-15C divergence between cells on mine under some conditions) this causes imbalances in cell capacity degradation that over time result in cells degrading at different rates to each other, and this is not a good thing.

Liquid cooled packs are able to keep the individual cells at a much more uniform temperature which means cell degradation across cells will also be much more uniform, which is a good thing.

Cooling of cells while charging is done with a chiller which is basically an A/C compressor (although on liquid cooled packs it is chilling liquid coolant instead of air) and these typically have a COP of about 3 - this means it takes a lot less energy to cool a hot pack than it does to heat a cold one with a resistive heater. (Since a heat pump won't be effective at -20C and below)

So the energy penalty to cool a hot pack during charging is not actually that great, and it comes out of power supplied by the charger anyway, so again doesn't affect range.

On the contrary to what you say that it's a waste of time, one of the number one features I'll be looking for in my next EV is one that has liquid thermal management for the battery pack, both cooling and heating.
 

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It is interesting that everyone except Nissan has battery thermal management. Clearly you're right and they're all wrong.
Well they all have thermal management. LEAF and e-GOLF do it entirely in software. Charge / Discharge rates are limited when the battery is too warm or too cold.

E-Golf does not have active thermal management. Active cooling was initially an option on i3. BMW made it standard some time ago.

Kangoo Z.E. does not have active cooling or rapid charging. Renault say the van does not have either because of cost.

eNV-200 has active pack cooling.

Outlander PHEV has active pack cooling. I was surprised when I saw that.
 

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Benefits of passive thermal management:
  • Cheap
  • Simple
  • Less parts to go wrong
Hence a great solution when it is works well, for example an electronic wheelchair. It can also be "good enough" for a car that is mostly charged at home and never driven hard for long distance in a mild climate like the UK.
 

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On the contrary to what you say that it's a waste of time, one of the number one features I'll be looking for in my next EV is one that has liquid thermal management for the battery pack, both cooling and heating.
i3 has the best design I've seen. i3 uses R134A direct from the AC system. The batteries sit on top of the of an evaporator. Heat from the modules is transferred to the evaporator by conduction. In very cold weather BMW use resistive heating. BMW mention an active air flap but I'm not sure what that does.

e-NV200 and Outlander both use air. There is an evaporator coil, fan and ducts inside the pack. Outlander has 1kW of battery cooling. The fan can run alone to balance the temperature. When that gets above a set value, the heat pump turns on. Like BMW there is a PTC heater in the pack to warm it up in extreme cold.


They all use a heat pump so power consumption is lower than the amount the heat removed.

Sources:

https://www.mhi.co.jp/technology/review/pdf/e512/e512044.pdf
Mitsubishi Outlander PHEV Forum • View topic - Drive battery Thermal Management.
 

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Hence a great solution when it is works well, for example an electronic wheelchair. It can also be "good enough" for a car that is mostly charged at home and never driven hard for long distance in a mild climate like the UK.
It is "good enough" for LEAF 30 in all but extreme cases.
 

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e-NV200 and Outlander both use air. There is an evaporator coil, fan and ducts inside the pack. Outlander has 1kW of battery cooling. The fan can run alone to balance the temperature. When that gets above a set value, the heat pump turns on. Like BMW there is a PTC heater in the pack to warm it up in extreme cold.


They all use a heat pump so power consumption is lower than the amount the heat removed.
The i-Miev/Ion/C-Zero use A/C air cooling for the pack during DC rapid charging as well.

They don't have an evaporator inside the pack as you describe for the Outlander but just use the normal cabin A/C system with a flap that diverts the airflow into the front of the pack enclosure and a second exhaust fan at the rear of the pack so that the car is both blowing cold air into the front of the pack and sucking the warm air out the back.

If all cells are below 20C the Fan/AC doesn't run at all, if any cells are above 20C but below 30C it runs the blower fans only for ambient air cooling, if any cells are above 30C it runs the A/C compressor as well with the duty cycle increasing the hotter the cells get. So apparently it is trying to target 20-30C as the optimal charging temperature.

This certainly works a lot better than nothing at all (hello Leaf!) but inevitably it can't cool the cells equally due to the physical layout of the cells and the way the air is forced to flow around them. So after a few repeated stretches of fast motorway driving and 20 minute rapid charging sessions the cell temperatures start to diverge by up to 10-15C which is not ideal. Another limitation is that it only cools the battery during charging, not driving.

Any forced air system is going to have the same cell temperature divergence issue - I've seen a "rapidgate test" video of the Ioniq (whose battery is air cooled) that was done by a German guy to compare it's performance to the Leaf back when rapidgate broke, and while it fared a lot better having at least some cooling, and didn't throttle the charge rate until he'd pushed it hard for a long time, (autobahn I think) there was still a very wide spread of cell temperatures after repeated fast driving and rapid charging sessions with some cells hitting as high as 50C during charging with others as low as 35C at the same moment in time. So a relatively similar result to the Ion under the same sort of stress test, despite the Ioniq also being able to run the battery cooling fan while the car is being driven.

Since it only takes one bad/weak cell to limit the usable capacity of a pack, even one cell that gets a lot hotter than the rest under stress would cause premature degradation of usable capacity.

This is where conduction based liquid cooling really shows itself to be superior - it can cool all the cells much more evenly regardless of their physical position and layout as it is not reliant on airflow. The cells have heat conducting tabs which then conduct the heat directly to the coolant heat exchanger interfaces. There will be a small temperature gradient between the cells that are "first" in the coolant loop to those that are "last" (of about 5C) but this can be minimised by having several parallel coolant paths so that a given coolant path doesn't pass too many cells.

Liquid cooling is definitely the way to go. While I think we'll continue to see air cooling on cheaper / lower performance / short range EV's, liquid cooling makes sense for any higher end EV, any EV with high performance (acceleration and charging speeds) and any EV with long range. (Since long range means longer driving/charging times hence more time for the battery to heat up)
 

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The Ampera uses liquid for thermal management and can when needed heat and cool the batteries.
The lack of problems with the batteries is a testament to the system.
 

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If all cells are below 20C the Fan/AC doesn't run at all, if any cells are above 20C but below 30C it runs the blower fans only for ambient air cooling, if any cells are above 30C it runs the A/C compressor as well with the duty cycle increasing the hotter the cells get. So apparently it is trying to target 20-30C as the optimal charging temperature.
Outlander is the same. They really did just stick everything they'd learned into the Outlander.

We can see the Outlander cooling system in this teardown video. Cooled air flows from the centre of the pack and around the cells before returning up the sides to the intake side of the evaporator.


Skip to 2:15

 

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Unless they make a new battery with high density and not particular sensitive on temperature (above 30 and below -10), which at the moment does not exist, the battery thermal management it is practically mandatory

Here is a nice link to a EV battery specs : https://www.gs-yuasa.com/en/technic/vol5/pdf/05_1_021.pdf
Page 5 shows precisely that battery degradation is double faster with a battery temperature at 45C vs 25C

What I'm not convinced is what is the impact on battery life when battery temperature is below 0C.

The battery in the specs above claim to be able to handle charging from -25C up to 60C ...
1C charging is supported above 0C up to +55C
At -25C charging should be limited to only 0.2C

It would be interesting to see battery degradation not only for 25C and 45C .. but as well for 0C .. for get an idea when an active battery heater is needed.

Some active thermal management are not working when the car is unused .. so leave under the sun a BEV/PHEV in some country may bypass the thermal management ...

PS: I know my PHEV is designed to keep the battery under 35C .. but it has no protection when the car is not used .. but in general, in most of europe it is difficult to get above 35C in the battery compartment even when parking outside under the sun. Normally the cabin temperature can go above 45C .. but the battery sitting on the bottom of the car normally are fully isolated from the sun influence .. and outdoor temperature above 35C is exceptional in most of continental europe
 

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Here is a nice link to a EV battery specs : https://www.gs-yuasa.com/en/technic/vol5/pdf/05_1_021.pdf
Page 5 shows precisely that battery degradation is double faster with a battery temperature at 45C vs 25C

What I'm not convinced is what is the impact on battery life when battery temperature is below 0C.

The battery in the specs above claim to be able to handle charging from -25C up to 60C ...
1C charging is supported above 0C up to +55C
At -25C charging should be limited to only 0.2C

It would be interesting to see battery degradation not only for 25C and 45C .. but as well for 0C .. for get an idea when an active battery heater is needed.
As far as I know below 0C temperatures would cause less age related degradation than 25C would as degradation is caused mostly by unwanted chemical side reactions that are accelerated by higher temperatures. So from that perspective colder is better.

The risk from low temperatures for Lithium Ion batteries is dendrite formation - which only occurs when charging, not discharging. Charging too fast at low temperatures causes metallic lithium to deposit on the electrode receiving the ions in the form of whiskers. Once formed they are a permanent and can't be removed again by discharging or any other kind of rejuvenation process.

The Lithium Ions that form lithium metal whiskers are no longer "mobile" in the electrolyte and thus cause an immediate loss of capacity (degradation) by the amount of lithium that is now trapped in metallic form.

But the more serious issue is that every time you charge the battery too fast at cold temperatures the dendrites will continue to grow like icicles until eventually they reach across the electrolyte and touch the other electrode and short the cell out. At that point the cell is likely to melt down and/or catch fire so it and most of its neighbours will be destroyed. Depending on the battery pack design the entire car may catch on fire.

(Some EVs like Tesla have very sturdy metal firewall enclosures and downwards pressure relief vents to avoid this, some cars just put a plastic lid over the top of the battery enclosure and hope for the best!)

This dendrite growth issue is why lithium metal electrodes aren't currently used in Lithium batteries despite them having theoretically much greater (many times) energy density. Nobody has figured out how to stop a lithium metal electrode battery from growing dendrites at least in a mass producible battery. This is one of the promises of solid state electrolytes as the electrolyte forms a solid physical barrier to prevent dendrites from growing through the electrolyte instead of the liquid/gel electrolytes currently used.

So to protect a battery at cold temperatures you only need to limit the maximum charging/regen rate to a safe level for the temperature. In extreme cold you would need a heater otherwise you couldn't charge at all.

Some active thermal management are not working when the car is unused .. so leave under the sun a BEV/PHEV in some country may bypass the thermal management ...

PS: I know my PHEV is designed to keep the battery under 35C .. but it has no protection when the car is not used .. but in general, in most of europe it is difficult to get above 35C in the battery compartment even when parking outside under the sun. Normally the cabin temperature can go above 45C .. but the battery sitting on the bottom of the car normally are fully isolated from the sun influence .. and outdoor temperature above 35C is exceptional in most of continental europe
Tesla's will use active heating or cooling if the battery gets too cold or hot while parked and turned off, however I believe the battery has to be a long way from the normal ideal temperatures before this happens - outside of something like +40C and -20C, then it will only do what it needs to to stay just inside this range.

If it tried too hard to keep the battery close to say 20C while parked in extreme conditions then it would end up running the battery down a lot quicker and ultimately reduce the amount of time a parked cars battery could be "protected" from thermal damage.

I'm not sure what other EV's will actively manage the temperature in a parked/locked car - unless you live somewhere that experiences extreme hot or cold weather it would be difficult to know.
 

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A other issue, even with the i3 system., as the cells are very large (compared to a Tesla) the temperature can be very different within parts of a single cell.

PS: I know my PHEV is designed to keep the battery under 35C .. but it has no protection when the car is not used
A PHEV unlike a pure EV has the option of not using the battery if it is too cold.

EV with long range. (Since long range means longer driving/charging times hence more time for the battery to heat up)
As the internal resistance will tend to be lower on a long range EV hence less build up of heat per mile of driving and per kwh of rapid charging, this may not be the case. (Consider a long range car with a very slow 0 to 60)
 

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I've never accepted the prevailing misconception that active thermal management is beneficial to BEVs, when driven in all but the most extreme climate conditions.
At the risk of stating the blindingly obvious, there must be some 'optimum' temperature at which battery life and performance is maximised.

The purpose of active temperature management is to keep the battery at that temperature, or as close as possible, for as long as possible.

It may be possible to create a special battery that can accommodate a wider range of functional temperatures. The cost of that can then be weighed against the cost of thermal management.

But it must STILL be the case that this advanced battery chemistry will STILL have an optimum temperature of operation.

Have I now explained the source of my own 'misconception'?
 

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This dendrite growth issue is why lithium metal electrodes aren't currently used in Lithium batteries despite them having theoretically much greater (many times) energy density. Nobody has figured out how to stop a lithium metal electrode battery from growing dendrites at least in a mass producible battery. This is one of the promises of solid state electrolytes as the electrolyte forms a solid physical barrier to prevent dendrites from growing through the electrolyte instead of the liquid/gel electrolytes currently used.
...
Thanks for the informations

Not sure if I got it right ... are you saying Lithium battery with metal electrodes are not used ?

So then the this dendrite growth should not be an issue (but maybe we are splitting the battery capacity degradation with the short and fire risk) , but still ... thermal management in BEV/EV it is also used for extreme cold location .. and as well, my PHEV without a battery heater, it is still slowing down the charge process (and regen too), when the battery are colder then +5C

Checking on wikipedia the positive Electrode is always Lithium with another metal ... (Nickel, or Iron or Manganese, etc)
 

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I've never accepted the prevailing misconception that active thermal management is beneficial to BEVs
Really? Amazing! Whats your view on Flat Earthers?
 

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A PHEV unlike a pure EV has the option of not using the battery if it is too cold.
Not really .. my PHEV need the main lithium battery for power the electric motor which will start the ICE

Even if the PHEV can be used when battery is "old" with poor SOH .. and this impact only the EV range .. still since people which got a PHEV woudl like to do as much as possible km in EV mode, and keep their daily commute in 100% EV mode ... I believe battery degradation is more visible in PHEV than not in BEV ... for example .. a tesla with 75% SOH, can do only 150mile instead of 200miles .. which should cover daily commute and just cause maybe 1 extra stop at a fast charging station ... while a PHEV with 75% SOH, might have only 15miles range instead of 20 ... so making impossible to make the daily commute in EV mode, plus the further issue that while SOH goes down, many trip might require to start the ICE only for few "seconds", causing to age faster also the ICE, plus have almost lost the advantage to make cheap commuting ...

Per how battery are dimension and used , I would say degradation is harder on PHEV then not on BEV ... the smaller the battery, and more stress it will get in the EV usage ... a regen brake of 30kw is nothing for a 100kwh battery, but it is a incredible fast charging and arming condition for a small 12kwh battery
 

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Thanks for the informations

Not sure if I got it right ... are you saying Lithium battery with metal electrodes are not used ?

So then the this dendrite growth should not be an issue (but maybe we are splitting the battery capacity degradation with the short and fire risk) , but still ... thermal management in BEV/EV it is also used for extreme cold location .. and as well, my PHEV without a battery heater, it is still slowing down the charge process (and regen too), when the battery are colder then +5C

Checking on wikipedia the positive Electrode is always Lithium with another metal ... (Nickel, or Iron or Manganese, etc)
I'm referring to the negative electrode, (anode) which is usually graphite in a Lithium Ion battery.

Normally lithium ions travel into the structure of the graphite and are "stored" there during charging. If the battery is too cold and you charge too fast they end up plating the graphite surface with metallic lithium instead.

Storing Lithium ions in a graphite electrode has a much lower energy density than using a metallic lithium electrode. It's possible to make a cell with a metallic lithium anode but usually it won't last long because instead of plating evenly dendrites will grow with cycling and eventually the cell will fail catastrophically after a fairly short lifetime due to a short. So cycle lifetime and safety are both very low.

So I don't think anyone is currently doing this in production batteries. There are always people trying who say they've solved how to do it of course. For example these guys by using a solid separator:

The Lithium Metal Battery Is (Almost) Here | CleanTechnica

Until I see a battery technology in mass production I'm usually skeptical though. There are a lot of designs that work on button cells in labs but don't scale up to high power/long life applications like an EV where they need to last for 10-15 years under hostile high stress environments and be extremely safe. (The example above only has a 50 cycle life, which is very short, especially for a car)

"You can get twice the energy density" looks good on paper but "however your car will probably catch fire eventually" would put people off. :D
 

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A other issue, even with the i3 system., as the cells are very large (compared to a Tesla) the temperature can be very different within parts of a single cell.
Perhaps. Tesla put their cells in groups too. I don't know what the cell temperatures are. Just because it is Tesla and glycol doesn't make it better. Keep reading....

What I do see is that BMW's system is simpler and appears more durable.


The BMW modules are wrapped in aluminium that sits right on top of the cooling loops. Aluminum has low thermal resistance. The centre of the module could be a hot spot.

maxresdefault.jpg




Another good video of the BMW pack cooling.



The original Tesla cooling had a single ribbon for each module. The cells at the end of the 444-cell string will see warmer coolant the the ones at the head.




Slide1-2.jpg



The P100 battery has two cooling loops -- Each one cools 258 cells. Better.

Slide2-2.jpg



M3 is improved with more parallel cooling.

Outside of the pack a liquid plumbing system is pretty complex. Even in the simplified and improved M3 there are a lot of pipes, connectors and fittings. All that plastic is going to get brittle with age. Owning a 6-10 year old MS or M3 could be very interesting. Every few months one more plastic part is going to fail - usually at the worst possible time.




Tesla Model 3 Battery Cooling Much-Improved ... Track Mode?
 
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