Do lipo's need to breathe?

O

onemanmob

10 mW
Joined
Feb 3, 2014
Messages
21
Location
Los Angeles, CA
Hello! Pretty sure I'm going to end up using Lipo's for my rig but I do have some questions about packaging:

While researching the batteries I've seen more than a few people claim that applying pressure (not a lot but enough to restrict too much expansion) to the packs helps diminish swelling and can lead to a more constant resistance level. It is never backed up by anything scientific but personal opinion.

Also if I were to package the batteries in a PVC container would there need to be vents to allow for off gassing or heat dispersion?


Thanks!
 
Every charge and discharge, they expand and contract. Healthy pouches do not need ventilation. Pressure through the cells Z-axis in the range of 2-5psi is optimal for ensuring a long life with low impedance.
 
If you buy hardcase packs (bricks) then you might not need to worry about it.
 
liveforphysics said:
Every charge and discharge, they expand and contract. Healthy pouches do not need ventilation. Pressure through the cells Z-axis in the range of 2-5psi is optimal for ensuring a long life with low impedance.
Click to expand...

Can you please comment/advise if you're aware of any battery pack designs involving pressure gauge measurement to trigger alarm for puffing or when lacking ample pressure to maintain optimum IR?

I'm staring at the sensor from small, cheap, kitchen scale and wondering if something like this might be worth exploring as another source of data to help better protect battery cells when assembled into packs?

Always good to read your stuff - many thanks!

OP - please forgive me the hijack but it appears the question had been answered.
 
if you are gonna recommend people use those hardcase packs because you think they provide compression you should cut one of yours open to see how wrong you are.

they do not provide uniform compression. there are pieces of double stick foam set in two or three places and the rest of the pouch is unsupported so the pouches inside are deformed dramatically because of that poor design.

people should not use them, and should not recommend others use them either.
 
it was not jacking the thread. the hardcase packs are the worst for providing the kinda uniform pressure across the electrodes that you need to maintain. the foam tape inside distorts the electrode sandwich by creating high pressure in a few spots and low pressure in others so that causes the cathodic matrix to move under hydraulic forces internally and makes the spots where the foam tape is present to be thinner than the other spots along the surface of the pouches.

unless you have opened a hard case and could see this you would not know it so you might assume that advice was appropriate.

the hardcase pack is for the guys who wreck their RC cars all the time and the hard case keeps the pouches from being punctured.
 
I was referencing Ykick's comment:

OP - please forgive me the hijack but it appears the question had been answered.
Click to expand...

like I said, no big deal. Sometimes thread jacking can lead to information that is still relevant to the original question :)
 
Onemanmob imformation hear comes from many veiws and glad you notice that questions answered arn't the questions asked but still very useful.
As make sure you check for duds before pack build. Plus I would have a vent hole.
 
dnmun said:
it was not jacking the thread. the hardcase packs are the worst for providing the kinda uniform pressure across the electrodes that you need to maintain. the foam tape inside distorts the electrode sandwich by creating high pressure in a few spots and low pressure in others so that causes the cathodic matrix to move under hydraulic forces internally and makes the spots where the foam tape is present to be thinner than the other spots along the surface of the pouches.

unless you have opened a hard case and could see this you would not know it so you might assume that advice was appropriate.

the hardcase pack is for the guys who wreck their RC cars all the time and the hard case keeps the pouches from being punctured.
Click to expand...

I've also opened hardcase packs after use in RC cars and seen the insulation/wrap worn almost right through due to the pack moving within the case - I wouldn't use them unmodified on an ebike either.
 
I have several RC cars and several LiPo batteries which I've run until they can no longer provide the current I desire. Even hardcase packs will swell. The packaging is stronger and more rigid than your normal shrink wrapped LiPo batteries, but it still has enough flexibility to allow the LiPo to swell. From what I've read, swelling is normal. Manufacturers try to keep it between 5% and 10% of the original size.

The main cause of puffing LiPo batteries is over discharge. Treat them with respect, make sure you draw less than the normal C rate (burst rate is only what it says, BURST), follow the 80% discharge rule and you should be ok.

I also think LiPo batteries do need to breathe. My LiPo batteries in one of my RC cars used to get quite warm after use and swell a bit, until I drilled holes in the battery compartment allowing the batteries to dissipate heat. Now they stay nice and cool, and don't swell up and get stuck in the battery compartment. Excessive heat is a killer of LiPo cells.
 
Hobby King has a sales blurb on their nanotech in which they talk about how the nanotech swells less than the regular lipo.

from what i have read there is a point where the volume change in the cathodic matrix is significant as the pouch is drained below 50% capacity. this shrinkage is supposed to be why discharging below the 3.5V level is harder on the pouches. even though not fully discharged.

the lifepo4 puffers i have seen were mostly if not all from over discharged under load. down below 1.8-1.6V. i have overcharged lifepo4 for very short time to 4.4V with no apparent damage but the ones that got to 5V never recovered full capacity. it may be that lipo is similar about overcharge. maybe just a little for a short time is ok but a longer time, especially high charge currents, maybe are hardest.
 
dnmun said:
Hobby King has a sales blurb on their nanotech in which they talk about how the nanotech swells less than the regular lipo.
Click to expand...

Don't go believing that. My Nanotech LiPo batteries swell as much if not more than my Gens Ace LiPo's. Both batteries are about the same age, usage and C rate.

Also, the Nanotech A-spec LiPo's don't seem to be worth the extra money as tested and reviewed here:

https://www.youtube.com/watch?v=P-TCOYk-QSs

dnmum, you are correct, over discharge is what harms LiPo the most. I've set my LVC on my RC controllers to 3.3V per cell up from 3V and although I get less run time, there is noticeably less swelling (if any swelling at all) by the time LVC kicks in.
 
Punx0r said:
A lot of RC LIPO users on here only discharge to 3.6-3.7 VPC...
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True, but my controller programmer only allows LVC to be 3.5V per cell or even less :p
 
They have two separate and unrelated gas production methods.

Left at high voltages (> 4.15ish) the curve for electrolyte decomposition from electrolysis produces gas byproducts that inflate the pouches.

Over - discharging produces gasses from the collapse of anode structures and associated mechanical damage to the SEI upon heavy de-lithiation of the formed anode assembly.

Over discharging further <2v consumes the copper anode foil as the next available (yet much lower potential) ion source to consume after total de-lithiation. (because the graphite anode material has nothing left to donate, so the copper is the next sacrificial ion source).

That's why it's very rarely a danger when a battery is simply slowly discharged to 0V, but upon a recharge attempt when the copper ions precipitated into internally shorting dendrites that you encounter the danger potential. When you're lucky the internal shorts stay very tiny and the cell just self - discharges at a thermally safe rate (and typically locally gasses from tiny local hotspots). When unlucky, it can result in spontaneous and impressive ignition during charging.

Hence why you want to keep it in the 4.1-4.15v to 3.6-3.7v range, and if by chance you botch something and deeply over-discharge, at the bare minimum recharge them in a BBQ pit or something, and by all means of you're going to risk the recharge rather than tossing them, do it as soon as you notice the low voltage (to minimize consumed copper) and do it at a low rate, like C/4 or similar. Then if you notice some cells are leaking down on there own, destroy those cells, you don't want them in your pack.
 
Love it when you comment, and I learn why what I was told works best works best.

Re the lipo breathing, the pack does not need to breathe. But other LFP posts about hot batteries do indicate that in some cases cooling a battery could be good. If you need to vent electrolyte, you have holes and need to look into why you smell it. As said above, hard packs are very poor cell protection.

But IMO, if your lico packs get really hot in discharge, you are discharging at too high amps. Ignore the pretty numbers on the side of the batteries. If they are getting that hot, you need more capacity, less controller, or better c rate cells.

On the other hand, if it's for a race you might want to use your battery in a way that quickly destroys it.
 
dnmun said:
if you are gonna recommend people use those hardcase packs because you think they provide compression you should cut one of yours open to see how wrong you are.

they do not provide uniform compression. there are pieces of double stick foam set in two or three places and the rest of the pouch is unsupported so the pouches inside are deformed dramatically because of that poor design.

people should not use them, and should not recommend others use them either.
Click to expand...

No, it is you that practices uniform compression. They provide the correct expansion room and meet their specification. Chopping them up and pressing them between boards is your method, but it is not the manufacturers. Who should I believe is right. On one hand I have millions sold and I have found it true myself. On the other hand, I have a couple of forum users.

My original post is bang on. Buying bricks is easy, which is why so many people here do just that. This is the first time I have heard something meaningful said against them. Which was the fact they didn't rub through during their lifetime, but it looked close to a forum user. That is still not really a great deal said against them. Not when you think about how many of us buy these a dozen at a time.

You can carry on buying them, chopping them up and taking off coloured wires to fit white one's if you like. I think it's a lot of work for nothing though and your the only one I see doing it. Your a fringe user. Hardcases are mainstream. Your opinion is not the norm. I didn't post about hardcases to back up your compression talk, that was just your wishful thinking. Hardcases prove a million times over that they are fine without covering them in gaffer tape.
 
From a few posts up:

liveforphysics said:
Every charge and discharge, they expand and contract. Healthy pouches do not need ventilation. Pressure through the cells Z-axis in the range of 2-5psi is optimal for ensuring a long life with low impedance.
Click to expand...

Ergo, significant compression = good, "expansion room" = bad.
 
lipo is like a lungfish that has crawled out of the water on to land.

it needs to breathe.

when your bike runs over the lungfish, it makes a dent in the lungfish where the front tire runs over it and then it makes a dent where the back tire runs over it.

so now you have a lungfish outa water with two big dents in it. that is what the pouches inside a hardcase pack look like after the pouches swell against the strrips of double stick foam. except there are three dents so you know it is not caused by a lungfish crawling outa the water and getting run over by your bike. wonder what coulda caused it. duh.
 
I have never compressed my lipos because i know that they naturally expand and contract and don't want to mess with that. My 4 year old 20C turnigy packs are still running great and still have good discharge after ~200 cycles.
 
dogman said:
But IMO, if your lico packs get really hot in discharge, you are discharging at too high amps. Ignore the pretty numbers on the side of the batteries. If they are getting that hot, you need more capacity, less controller, or better c rate cells.
Click to expand...

Yes, this.

I run a big 20AH 20C pack with an average draw of 2C-4C on it for 75% of it's life. I can never get the cells to feel warmer than ambient temperature under this use.

Meanwhile i know someone who used their 20C pack at a 20C draw... his pack lasted 75 cycles and puffed out really badly. I told the guy it was a bad idea and he did it anyway and came back to the forum crying about it a few months later.
 
I got a similar result, using 30 c packs at 8c, AND some discharges to 3v or so. Those packs died at 50 cycles. Generally, just one cell really gave up the ghost. The remaining cells got made into smaller packs that lasted.

Now I try to keep c rate to below 5c, and judge by having a cooler pack at the end of the ride. If that pack gets much hotter than body temp, I get more battery on that bike next time.
 
Came across this topic as I am into 1p lightness, as a result I have heating batteries and am looking for solutions. Not ready to pay for big buck C ratings either.

The idea that popped in my head is that although it is far from perfect, and will not apply to 2p 3p 4p etc set ups:

There must be some strong relationship between motor heating and battery heating. If we don't have a product that can regulate our battery heat, but we do have a cav3 that can monitor motor heat then make a stronger connection between motor heat and battery heat.

So if you battteries are getting hot lower the temperature the amps should be lowered when the motor heats up. I hate to think I won't to get to at least blast my set up occasionally, so just always using less amps will suck.

I use my bike recreationally so this wouldnt suit many commuters who are allergic to pedalling and prefer to carry a ton of batteries.

For me I am scared of wiring and more than series -ing batteries, don't like the idea of charging where I can't see every cell's v or monitoring discharge in a similar way.

I am going to lower the temperature start point to lower my amp draw by heat of the motor now, was 90-130 degrees before, will try 60 degrees as an entry point first, and then toggle back and forth until the batteries stop being more than an acceptable warmth.
 
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