How Do Most Lithium Ion Batteries Behave When They Are Approaching End Of Life?

JAS

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As posted above, do most lithium ion batteries just have a shorter run time, simply not hold a charge or something else?
 
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john61ct

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mAh capacity declining is the easiest symptom to benchmark, 70-80% is a good EoL definition, for most LI chemistries

which get much more prone to thermal runaway, boom bad.

IR rising a bit trickier.
 

ChrisGarrett

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mAh capacity declining is the easiest symptom to benchmark, 70-80% is a good EoL definition, for most LI chemistries

which get much more prone to thermal runaway, boom bad.

IR rising a bit trickier.

Thermal runaway is now mostly a thing of the past, with the discontinuation of true lithium-cobalt chemistries.

You're correct in stating rising I.R.s and lower capacities, as being signs of a declining cell.

And then it was mostly an issue of 'charging' cells back up that were stored near zero volts, where copper dendrites could form.

Not saying that modern cells can't get to a thermal runaway point, but it's not much an issue with modern cells and chemistries.

Chris
 

john61ct

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Not **as** easy to do

is far from "now safe".

False sense of security actually increases the risk for noobs.

With bigger like RC sized packs fires regularly burns houses down.

It's knowing what you're doing that reduces to risk.

And using LFP or LTO if you don't really need the high energy density of the 3.6-3.7V chemistries
 

MarioJP

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I would like to point out from first hand experience is while they are charging, they start to get warm at the cv phase as current starts to dip.

Sometimes it does not terminate and just stays red longer than it should on one of the cells while temp slowly keeps going up.

The weird thing though, is that it will terminate sometimes on that cell in question. Even put a piece of tape to mark it.
 
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WalkIntoTheLight

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I would like to point out from first hand experience is while they are charging, they start to get warm at the cv phase as current starts to dip.

Sometimes it does not terminate and just stays red longer than it should on one of the cells while temp slowly keeps going up.

The weird thing though, is that it will terminate sometimes on that cell in question. Even put a piece of tape to mark it.

That's normal for worn-out cells.

The reason is that the cell can not hold a full 4.20v charge anymore. It might have a resting voltage closer to 4.05v (for example). So, when the charger attempts to fill it further than 4.05v, a lot of the charge is lost to heat as the cell has difficulty retaining that charge.

You'll find that it takes a very long time for the charge to complete at 4.20v. The charger goes into the CV phase, and it just keeps dumping in a small amount of current (say 100mA), while the cell is shedding most of that into heat as it tries to self-discharge. Eventually, the charger may get close enough (it has a pre-determined CV current where it will cut off), that it marks the cells as full and stops charging. Or, it may never get there.

If you measure the cell voltage after charging, you'll notice it has fallen down to 4.10v or lower, after just a few minutes.

Anyway, the point is that worn-out cells don't hold much capacity, they don't hold a full charge, and they have awful internal resistance.
 

john61ct

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For better longevity with these chemistries better to charge Bulk/CC only and stop at 4.05V starting from when they are brand new anyway, maybe 4.1V

Going all the way to 4.2V, much less holding any CV is very stressful and reduces lifecycles a fair bit.

Most only last a couple hundred cycles anyway, especially at high C-rates.

Using such cells past their EoL point really increases the risk of thermal runaway,

Boom Bad!
 

WalkIntoTheLight

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Using such cells past their EoL point really increases the risk of thermal runaway,

Boom Bad!

Well, I'm not sure there's any evidence of that. Maybe if you're trying to drive them at a constant 20 amps under a regulated driver. But I'd worry more about thermal runaway in new cells if you're doing that, as they probably can run for a lot longer which gives time for internal heat to build up.

Generally, worn-out cells just have such poor performance, that they're not worth using. Throw them away, and buy new ones.

If you notice they have self-discharge, regardless of the resting voltage level, then throw them away faster. They have developed an internal short.
 

john61ct

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The most dangerous time for LI batteries "exploding" is while charging not discharging.

There are hundreds of events recorded as evidence of this danger

not saying the use cases represented in this website are especially risky nor safer.

If you're starting with quality new cells and routinely recycling them as their capacity loss becomes evident

then that is likely to prevent any such problems.
 

WalkIntoTheLight

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Again, I'm not aware of any evidence that shows worn-out lithium-ion cells are any more dangerous than new lithium-ion cells. If you abuse either one, you risk them venting, catching fire, or even exploding. However, a new lithium-ion cell can store a lot more energy than a worn-out cell, so the risk is even greater, IMO.

The reason to buy new cells is not for safety, but because old cells have poor performance.

That said, old cells can develop internal shorts, and you need to watch out for that because it is a safety concern. However, I have had 3 new cells develop internal shorts, and they only had about a dozen cycles on them. So, it's not a problem specific to old cells.

And yes, when charging, you need to be careful, with all cells.
 

MarioJP

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Good points, surprisingly though, they are still good at charging my phone from low to full even with reduced capacity. But i do notice that the battery% on the power bank does drop easily when charging a device. By the time it fully charges the device, the power bank went from 100% to around 50-45% on a single use. I currently using 4 NCR18650B for my power bank. These cells are at least 4 years now.

I have reduced the charging speed to 500mA and set to terminate when it hits 200mA at 4.20v Sometimes i just don't use the external charger and have the power bank charge them.

Before, i used to have it terminate at 60mA. This charger allows you to set the termination as low as 0. I know that can't def be good for the battery for a perfect top-off charge lol. That's just unrealistic to be honest.
 
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Kurt_Woloch

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Generally speaking, the IR rises, and the capacity declines. The capacity curve is similar to the discharging curve in that there is a "knee" where it's very flat, but after that it starts to drop faster and faster.
Here are some values from my laptop where I went through a complete battery until it reached about 50% of its original capacity, and before that...
on the first cycle it had 105% of it's rated capacity,
Cycle 12 yielded 102%,
Cycle 58 yielded 97%,
Cycle 125 yielded 95%,
Cycle 236 yielded 93%,
Cycle 313 yielded 91%,
Cycle 402 yielded 85%,
Cycle 456 yielded 75%,
Cycle 537 yielded 66%,
and Cycle 580 yielded 50%, after which the battery was retired.

On Cycle 537, the IR also was abut 2.5 times as high as with the fresh cells.

As you can see, the curve was very flat between cycles 125 and 313 and started to drop more and more sharply after that. That was, however, a battery bought in early 2012 and used util late 2016, which has been a few years now, so your results may vary...
 

john61ct

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Again, I'm not aware of any evidence that shows worn-out lithium-ion cells are any more dangerous than new lithium-ion cells.
That is simply a limitation of your knowledge and exposure, there is no doubt it is most definitely the case.
 

Stoneking

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I can't find any articles stating worn or aging cells are more dangerous.
I would be interested in some form of study or proof of this.
 

cy

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I was part of the original group of CPF'ers that were amongst the world's first use of lithium ion cells in flashlights. lots of explosions back then starting out when very little was known about then emerging technologies for individual use of li-ion cells.

have been using those same batch of early lithium cobalt cells since then. it makes a huge difference for safety and longevity related to which li-ion charger you are using.

what I've noticed over a decade+ of using those early li-ion cells is .. lithium cobalt cells will first start losing it's ability to hold a charge. for instance after cell reaches and/or attempts to reach 4.2v during charge cycle, charger will then indicate cell actually is holding say 90% or whatever. then cell in following charge cycles will start holding less and less .. followed by cell failing to hold a charge at all.

above is for early lithium cobalt cells charged individually with a state of the art li-ion charger in a clamp mod mentioned in sig. over the years I've upgraded li-ion chargers/power supplies especially as different chemistries emerged.

please note my preference for quite sometime when using lithium cobalt cells .. is to use flashlights that allows single cell configuration. Amazing how far lithium technologies has progressed.
 
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