Questions on Li-Iron Phosphate Porsche Battery

I am driving a Porsche Cayman S. The track oriented "R" version of this car saves weight by using a Li-Iron Phosphate battery, instead of a conventional lead-acid one:



Since this battery is available as an option for my car and given the merits of lithium chemistry, I was thinking that this was a nice idea. Not that the saved weight is so important for me but I do like saving weight when it comes to a car. Besides, this is a cool idea, this offers a wow factor, etc… I didn't buy it but I would consider doing so, should I need a new battery for my car. On the other hand, this would most probably be so expensive that I would stick to a conventional battery, anyway.

In the meantime, I became a CPF member and the more I get enlightened, the more I realized that the interior of a car is not a good place for Li-Ion batteries, due to heat being an important factor for them. Therefore, does the existence of this battery mean that Porsche compromises battery life for the sake of saved weight, or, does this mean that Li-Iron Phosphate batteries are considerably less sensitive to heat than Li-Ion batteries?

I guess the truth will be something in between and I would be delighted if battery gurus chime in and interpret what exactly this Li-Iron Phosphate Porsche battery is about. Thanks.

Hello Bucur,

Many people are using those batteries in cars and motorcycles. They seem to handle the conditions well and perform well. They are somewhat more expensive, but I don't think they are all that bad.

As far as heat goes, keep the interior of your car below 140 F (60 C) and there should be no problems for the battery.

Tom

Thank you, Silverfox. I didn't know that these batteries were used by many people but unless they offer substantial additional benefits on top of weight reduction, I won't be one of them because I learned, today, that this battery is not a bolt-on replacement for my car. It requires some modifications on the brackets and I am a bit reluctant when it comes to modifying them.

What you say on heat is very enlightening for me. What I understand from various posts at CPF is that Li-Ion battery powered flashlights should not be kept in fully charged state in cars because temperatures exceeding 25 C (77 F) is not good for Li-Ion batteries, and that 60 C (140 F) is a horrible condition for them.

Since car batteries are always fully charged (as long as the car is used regularly) and since not exceeding 60C (140 F) is OK for Li-Iron Phosphate batteries, may I conclude that the latter is much less heat sensitive than Li-Ion batteries?

I am asking this because after learning how sensitive to heat Li-Ion batteries are, I am now concerned for the Li-Ion battery powered flashlights that I am keeping in my car. On the other hand, if my car was equipped with this Li-Fe battery, the car battery would be subject to even more heat than the flashlight batteries actually are. Therefore, I conclude that Li-Fe batteries are substantially more heat tolerant than their Li-Ion cousins. Is this correct?

Thank you.

Hello Bucur,

The upper limit for operating temperature is 140 F. If you operate at that temperature it will take its toll on the batteries and you will find that you have to replace them sooner.

Most people find 140 F very uncomfortable so personal carry tools like flashlights usually never see this but a cars engine compartment is different.

The Li-Fe cells are very robust, but can be damaged. It just takes a lot more to do that.

Tom

I have that one in my motorcycle for going on 3 years, and think it is great.

SilverFox said:

Most people find 140 F very uncomfortable so personal carry tools like flashlights usually never see this but a cars engine compartment is different.

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So is a car's interior, when the car sits some time under direct sunlight in Summer. I wonder if this reaches 140 F but it does become very uncomfortably hot. If there are some rechargeable Lithium batteries in the glove compartment (not under direct sunlight) of such a hot car, does it significantly matter if these are Li-Ion or Li-Fe chemistry?

Davekan said:

I have dad one in my motorcycle for going on 3 years, and think it is great.

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Thanks for letting me know, Davekan. I wonder how different things would be, if your motorcycle battery was Li-Ion but not Li-Fe...

Hello Bucur,

Let's start with the understanding that heat kills batteries.

From there I can say that Li-Fe are a little more tolerant of heat than Li-Ion. I don't know if there has been any testing that shows the actual difference.

Some people store their lithium and Li-Ion lights in a small cooler if they are going to be kept in the car during the summer heat. This tends to temper the maximum temperature a little.

Tom

Silverfox, thanks to your informative posts, as well as some others, I do understand that heat kills batteries and I am happy that I learned this. On the other hand, I may have "over-understood" this phenomenon because I was thinking that the Li-Ion flashlight batteries that reside in the glove compartment of my car, inside the flashlights, were being tortured. I now understand that keeping rechargeable Lithium batteries cooler would definitely help, but that not doing so should not be considered as torturing them.

I have recently noticed that Porsche even uses Li-Ion car batteries for the race oriented models of their 911 series [Tequipment 911 Catalogue (accessories for the 911 model range) page 40-41]:

Lightweight battery
(lithium-ion, not shown)
For the first time, Porsche is
offering a lithiumion
battery designed for use on the racetrack.
The key advantage of this
battery is that it can be swapped
easily for the conventional
standard battery to deliver a
weight saving of over 10 kg,
and increased performance.
Only for 911 GT3, 911 GT3 RS,
911 GT3 RS 4.0 and 911 GT2 RS.

The fact that the Li-Fe battery for the Cayman R and the Li-Ion battery for the 911 are special applications (track use or racing) was still a concern for me but since you say that "many people are using them in cars and motorcycles", one of them being Davelan, I am now much less concerned than before. I have no doubt that my car battery is subject to considerably more heat than the 18650 batteries in the flashlights that reside in the glove compartment. Replacing them as often as I replace my car battery (not very often) would be OK for me.

Am I missing something?

Bucur said:

The fact that the Li-Fe battery for the Cayman R and the Li-Ion battery for the 911 are special applications (track use or racing) was still a concern for me but since you say that "many people are using them in cars and motorcycles", one of them being Davelan, I am now much less concerned than before. I have no doubt that my car battery is subject to considerably more heat than the 18650 batteries in the flashlights that reside in the glove compartment. Replacing them as often as I replace my car battery (not very often) would be OK for me.

Am I missing something?

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Keep in mind that, although 'Li-Ion' is often used around here to refer exclusively to Li-Co, Li-Fe is also a type of Li-Ion battery. Are you sure Porsche is actually using a Li-Co battery in the 911? Somehow, considering the less safe, less temperature stable nature of Li-Co vs Li-Fe, I doubt it. Not to mention that Li-Co has a FAR higher internal resistance (and FAR lower current capacity) compared to Li-Fe. Given the fact that the current output of Li-Co is pretty puny compared to Li-Fe, it would take ALOT of ICR 18650s or even 26650s to start a car.

StorminMatt said:

Keep in mind that, although 'Li-Ion' is often used around here to refer exclusively to Li-Co, Li-Fe is also a type of Li-Ion battery. Are you sure Porsche is actually using a Li-Co battery in the 911? Somehow, considering the less safe, less temperature stable nature of Li-Co vs Li-Fe, I doubt it. Not to mention that Li-Co has a FAR higher internal resistance (and FAR lower current capacity) compared to Li-Fe. Given the fact that the current output of Li-Co is pretty puny compared to Li-Fe, it would take ALOT of ICR 18650s or even 26650s to start a car.

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Thank you for chiming in, StorminMatt.

Nope, I am not sure Porsche is actually using a Li-Co battery in the 911 (as an optional item). In fact, I was surprised that the one for the Cayman R is Li-Fe but that for 911 this is Li-Ion. My guess is that this may be an oversight or negligence when printing the catalogue. What I am trying to figure out on this subject is about my deduction:

Since rechargeable Lithium based batteries are used in cars, keeping other rechargeable Lithium based batteries in the glove compartment of a car, inside a flashlight, should not be more detrimental for them (as far as heat goes), as long as the type used as car battery and the type used as flashlight battery have similar heat tolerance. This is why I am trying to figure out if Li-Fe (car battery) is significantly more heat tolerant than Li-Ion (flashlight battery). I would appreciate your input, especially after your comment that "Li-Fe is also a type of Li-Ion battery".

Nevertheless, Li-Fe can still be more heat tolerant than Li-Ion but is it? If so, is this to the extent of making Li-Fe a suitable car battery chemistry but Li-Ion unsuitable for even being kept inside a flashlight that is in the glove compartment of a car?

Hello Bucur,

Keep in mind that these different chemistries behave differently.

When starting a car you need a surge of power that doesn't necessarily need a lot of reserve capacity. Li-Fe is able to handle high currents, but has greatly reduced capacity.

On the other hand a flashlight user is usually interested in a decent amount of run time. Li-Co has great capacity and fills this need.

If you use Li-Fe cells in your flashlight you may be disappointed with the run time.

Tom

SilverFox said:

Hello Bucur,

Keep in mind that these different chemistries behave differently.

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Thanks Silverfox. Do they behave so differently that Li-Fe is suitable for being kept in a hot car but Li-Ion is not?

As I understand, the temperature at which thermal runaway starts is much higher with Li-Fe than with Li-Co. This alone suggests that Li-Fe is more tolerant of high temperatures than Li-Co. Not sure, though, whether Li-Fe is suitable for underhood use. Then again, the battery can always be mounted in the trunk if this is a problem.

As far as capacity of Li-Fe vs Li-Co, I've kind of noticed something odd. A Li-Co 26650 has little more capacity than a Li-Co 18650. Yet a Li-Fe 26650 has LOTS more capacity than a Li-Fe 18650. In fact, a Li-Fe 26650 has similar capacity to a Li-Co 26650.

SilverFox said:

When starting a car you need a surge of power that doesn't necessarily need a lot of reserve capacity. Li-Fe is able to handle high currents, but has greatly reduced capacity.
Tom

Click to expand...

StorminMatt said:

As I understand, the temperature at which thermal runaway starts is much higher with Li-Fe than with Li-Co. This alone suggests that Li-Fe is more tolerant of high temperatures than Li-Co. Not sure, though, whether Li-Fe is suitable for underhood use. Then again, the battery can always be mounted in the trunk if this is a problem.

As far as capacity of Li-Fe vs Li-Co, I've kind of noticed something odd. A Li-Co 26650 has little more capacity than a Li-Co 18650. Yet a Li-Fe 26650 has LOTS more capacity than a Li-Fe 18650. In fact, a Li-Fe 26650 has similar capacity to a Li-Co 26650.

Click to expand...

Thank you guys. I think these posts clarify everything.

Cayman and 911 batteries are under the front bonnet (cargo space), supposedly away from engine heat (mid and rear engine cars, respectively). However, their battery compartments is warmer than their glove compartments, even when the car is parked under direct sunlight in summer. Since this cargo space is dark (no windows) there is no greenhouse effect like the interior of the car but 2 radiators that cool the engine plus the a/c radiator are all up front, heating this cargo space like no other. The clothes in the suitcase get warm after a long journey, chocolate in the suitcase melts (don't ask me how I know this!), etc.. My flashlights never get warm to the touch because the glove compartment is not only dark as well, but also, better insulated and not internally heated. In short, the car battery is still subject to more heat than the flashlight batteries.

On the other hand, since "Li-Fe is more tolerant of high temperatures than Li-Co" I get it that the existence of Li-Fe car batteries does not constitute a direct reference for 18650 flashlight batteries that are kept in the glove compartment. I keep worrying about them, albeit a bit less than before.

As for capacity; the optional Cayman Li-Fe battery is only 18 Ah as opposed to 80 Ah for the standard lead-acid battery but when it comes to cranking power, the Li-Fe offers 480 A whereas the lead-acid offers 380 A! This is 26.3% more cranking power, despite 77.5% less capacity and 10 Kg lower weight!! For my car, the weight reduction is equivalent to adding 2.37 HP!!! Besides, saving weight offers dynamic advantages on top of improving power to weight ratio. IMO, this is too good to be true for track/racing applications.

However, I believe 18 Ah capacity would be scary for daily use. With the engine off; the parking lights, interior lights, audio system, etc., would drain the battery faster than one could say "I need jump cables". The authorized dealer warns that no cranking power may be left in the standard 80 Ah lead-acid battery, within 24 hours, if only the ignition key is left on the car in "off" position (no visible and audible power consumption) because even in sleep mode, the electronic extravaganza drains that much. I also interpret this that so much cranking power is needed for starting the car.

Anyway, I will keep using lead-acid chemistry in my car and worrying about the 18650's in the flashlights in its glove compartment!