Just a strange thought

[CUDAcores89]

Everyone on here that has built or owned a battery means that at the very least we can all agree on one thing... Heat is bad for the lifespan of lithium-ion.

Heat also limits the amount of energy that can be discharged from a cell. Once a li-ion cell reaches a specific temperature, it will simply burst into flames and there goes your battery.

So here is a very strange thought. What if someone were to discharge a li-ion (or lipo) battery until it get's incredibly hot, then dunk the whole thing in a bath of liquid nitrogen?

I know for sure that dunking the battery in water would destroy it, but what about liquid nitrogen? Liquid nitrogen would not cause oxidation and destroy the cell, so in theory it might work. The idea is that the liquid nitrogen would keep the cell close enough to room temperature, and then the cell could stately discharge hundreds of amps. Yes, obviously this would not be practical for every day use. But would it even work at all?

In other words what I am trying to say here is if there was some way to actively cool a battery so that you could draw hundreds or even several hundred amps from it but keep the cell at room temperature, would it even work and thus allow you to draw as much current from the cell as possible vs keeping the ambient temperature at 70F thus limiting the current draw from the cell? Just a thought.

 

[Dauntless]

Well, can I go ahead and shoot this from a distance as you try it? Do you know the significance of differential temperatures having a little collision? You expect the cold to be inert?

 

[CUDAcores89]

Well, can I go ahead and shoot this from a distance as you try it? Do you know the significance of differential temperatures having a little collision? You expect the cold to be inert?

OK let's break down what I am trying to say. If there was a way to cool a battery, would that allow you do draw more current from it than at room temperature?

 

[amberwolf]

The colder a battery is, the worse it's voltage sag under the same current.

So actually the colder it is, the *less* current you can draw from it.

Check the spec sheets from cell manufacturers to see the specific temperature/discharge/charrge curves for any particular cell.

You can damage a cell charging it too cold, too.

 

[fechter]

Too cold would be bad also. With a forced-air (or nitrogen, CO2, etc.) you could keep the cells from overheating during high rate discharge. Some electric cars have this. When they are really cold, you want to heat them up before using.

There's other limitations besides the surface temperature though. It may be possible to damage the insides even if the outer shell is kept at normal temperature. As a test, you could take a single cell, short it, and dunk it in some water and see what happens. Water won't hurt in the short term. Distilled water would be better.

 

[Hillhater]

Some high performance commercial packs are actually built with the cells under full liquid immersion , with active cooling, to maintain performance and prevent damage.

 

[dogman dan]

The ideal would, I guess,, be keeping the battery at something like room temp. Above 80f is perky, below 50f is not. For best performance,, about 100f is perkier still, but that could be getting into more damage territory? I'm not sure. I am sure half the year I better be willing to use a battery that is at 110f. Can't ride inside where its AC cool.


We are pretty sure that the upper limits of a cells spec temp range is not good for sitting around fully charged. But using it at that temp?

My allcell pack is pretty saggy,, if worked at 20 amps much it gets nice and warm, like 110 ish. It has the wax that is supposed to help the inner cells cool. IMO,, it's not magic stuff, just some thermal mass the cell can warm up. In the more humid climates, air cooling a pack should work. But making the pack bigger so it does not sag like grannies tits works better.

 

[swbluto]

Many batteries have an internal resistance high enough and a thermal resistance high enough(from the core to the surface) such that, there's no way you can prevent overheating with active cooling if the current is high enough. But, it would help deter it in "normal usage". Active cooling plates/etc. between each cell would probably be best in this regard; flat cells would probably be more effective.

 

[dogman dan]

I may be really ignorant here, but I think most of the cooling strategies are aimed at trying to keep the core of a pack, deep inside the assembly of cells, from being a lot hotter than the edge cells.

Still gets plenty warm, just doesn't tend to sit there all hot for hours after the edges of the pack have cooled. Cool by top of recharge, at least.

 

[swbluto]

I may be really ignorant here, but I think most of the cooling strategies are aimed at trying to keep the core of a pack, deep inside the assembly of cells, from being a lot hotter than the edge cells.

What is true of the cell, is true of the pack. (Just saying the thermal-resistance/internal-resistance/heat principle applies to both cases. I /intended/ to mean the core of the cell.)

What is true of the individual, is true of the group.

What's good for the goose is good for the gander.

Lol, just found out gander meant "male goose". I always thought it meant something like lionride or banana:bunch.

 

[Ykick]

Why is it always about “cooling”? We all know cold battery packs suck and a comprehensive thermal management system should probably consider “warming” as well as cooling? At least for the charge station (like a block heater).

 

[amberwolf]

In my shed that I park my trike in, I have a couple of 100w incandescent bulbs keeping it about 10F warmer in there than it would be otherwise, since we've been having some nights down to the 40s and 50s F.

I'd rather not deal with any of the issues caused by the battery being that cold, when fully charged.

I don't have the battery area finished on the trike, which would insulate it from whatever the outside temperature is for a while, and it's too much of a PITA to unstrap it and take it in the house with me every night, then put it back on the trike every day. Otherwise I wouldnt' worry about it.

 

[Ykick]

Bro, I’m sitting here freezing 20F ('think it reached 22F for the high?) do you really need to mention 40-50F as your “that cold”? LOL…

40-50F really isn’t bad. It’s more noticeable sag but nothing like when it gets down around 15F. I mostly charge right away after parking so the internal temps are up anyway.

I did some testing years ago with RC Lipo in the refrigerator and freezer with wires running out to a charger and load test gear. And of course, riding sub freezing every year has provided practical understanding of how cold is too cold.

 

[amberwolf]

Bro, I’m sitting here freezing 20F ('think it reached 22F for the high?) do you really need to mention 40-50F as your “that cold”? LOL…

Thankfully it hasn't gotten below freezing this year so far, but there's another month or so in which it could, at night. Most years it happens down to about 20-30F at least a few nights.

But it gets pretty hot in the summer, up to 140-150F in the direct sun especially if it has to sit parked in it for a while.

40-50F really isn’t bad. It’s more noticeable sag but nothing like when it gets down around 15F. I mostly charge right away after parking so the internal temps are up anyway.

It makes a significant difference on my two older packs (one A123, one EIG), though not as much on my "newer" EIG pack (also built of old cells same age, but not used for at least a couple years, and not much before that).

There are supposedly also issues with charging a pack while warm (normal temps), then cooling it down (in my case, at least a 20-30F difference). I couldn't find the thread about it, though, and I don't remember the details, so it might not apply. But I always keep my stuff charged up because I don't always know when I am going to need the full range of it, and may not have time to charge it up before I do. So I charge as soon as I get home.

The newer pack doesnt' really warm up in my uses or charging, at least not noticeable in a "hand test", I have yet to instrument it and verify that, but I'm only using it at not even 2C peaks and less than 0.3C most of the rest of the time. Charging is only at a hair above 0.5C even for a fast charge at 24A, but normally I'd charge at just 4A with the Satiator, since it's an overnight charge anyway.

I did some testing years ago with RC Lipo in the refrigerator and freezer with wires running out to a charger and load test gear. And of course, riding sub freezing every year has provided practical understanding of how cold is too cold.

That's one thing I"m glad not to have to deal with..but the heat isn't much more fun (you can only take off so much of your clothes).

 

[swbluto]

Bro, I’m sitting here freezing 20F ('think it reached 22F for the high?) do you really need to mention 40-50F as your “that cold”? LOL…

/quote]


As a person living in an RV right now with little to no heating, I will confirm that anything below 55 degrees is COLD, lol, especially anything below 50. And I'm not talking about some BS "I feel cold" cold, I mean, your fingers no longer will move the way you want them to because they are frozen. How do I know? I'm a glorified computer worker and these things become self-evident in my situation, LOL. Further evidence comes from the fact it /never/ gets below 60 degrees around the equatorial, human's ancestral home.