Li-ion cells cycle ageing

Batteries, Chargers, and Battery Management Systems.
Alster   1 µW

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Re: Li-ion cells cycle ageing

Post by Alster » Jan 29 2020 11:35am

I don't vape or hunt , I do biking ( not ebike)
Hope the test will show how I should power my lights , 4 cell 21700 or 6 cell 18650 :roll:

docware   1 kW

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Re: Li-ion cells cycle ageing

Post by docware » Jan 29 2020 2:05pm

Alster wrote:
Jan 29 2020 6:49am
@docware

You have started testing 21700 Samsung 50E
Is it Samsung 50E or Samsung 50E2
It´s Samsung 50E.

docware   1 kW

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Re: Li-ion cells cycle ageing

Post by docware » Jan 29 2020 2:58pm

eMark, stop trolling here and stop sending me personal messsages, I am not interesting in any communication with you.

Can I ask admin for help and ban eMark ?

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Re: Li-ion cells cycle ageing

Post by john61ct » Jan 29 2020 3:17pm

Isn't there an ignore function?

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Re: Li-ion cells cycle ageing

Post by docware » Feb 03 2020 9:54am

Probably everybody here know negative impact of low temperatures on capacity and internal resistance of Li-ion cells, apart from aging during operation.

As I noticed some potential effect of temperature on DCIR during measurements, was wonder to know more. Not having temperature test chamber I made some provisory measurement to get some data on two cells, M36 and 29E7.
LG M36  DCIR versus temperature  50% SOC.jpg
LG M36 DCIR versus temperature 50% SOC.jpg (89.99 KiB) Viewed 1799 times
Samsung 29E7 DCIR versus temperature  50% SOC.jpg
Samsung 29E7 DCIR versus temperature 50% SOC.jpg (88.68 KiB) Viewed 1799 times
It´s obvious that mere 1 °C temperature difference has notable effect on resulting DCIR. These data are probably explaining sometimes little bit incoherent DCIR values of M36 and 29E7 during cycling testing where I use ambient air temperature measurement.
3.jpg
3.jpg (92.35 KiB) Viewed 1799 times
However the cell real temperature may be little bit different for various reasons, therefore for DCIR measurement is better to place thermocouple directly on the cell surface as I usually did for DCIR mapping.
2.jpg
2.jpg (73.43 KiB) Viewed 1799 times
Last edited by docware on Feb 27 2020 6:05am, edited 1 time in total.

john61ct   100 GW

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Re: Li-ion cells cycle ageing

Post by john61ct » Feb 03 2020 6:46pm

Yes too bad even the big cells they don't build in a temp sensor wire internally.

You can see why well-funded tests use a liquid bath.

Internally generated heat would really throw high-C rate results way off!

I guess do a test, wait an hour, do the next…

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flippy   1 MW

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Re: Li-ion cells cycle ageing

Post by flippy » Feb 05 2020 4:00am

puttin a sensor internally would be extremely cost prohibitve and serve no real purpose.
how would you plan to connect a couple hundred or thousand sensors to a board that can deal with that and what would the advantage be?
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Re: Li-ion cells cycle ageing

Post by john61ct » Feb 05 2020 7:41am

I think if a cell costs hundreds of dollars, at least giving an internal tube into the interior if nit an actual sensor would not be cost prohibitive.

Even just a couple of locations, one likely to hit overtemp first, another undertemp, would be useful in dynamically changing use cases.

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flippy   1 MW

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Re: Li-ion cells cycle ageing

Post by flippy » Feb 05 2020 7:58am

but a cell is less then a cup of coffee at the local McD, so thats not going to happen.

bigger cells are not cyclinderical and flat cells can very simply be equipped with a sensor.
your protection setup and use case should be such that any overtemperature behaviour is mitigated as such to prevent core temperatures to exeed the stated limits. usually this is done by giving the cell time to soak the heat to the outser cell.
this is also why you keep the temp logging going AFTER the discharge (or charge) test has completed so see the heat soaking process and you can make modifications to your planned battery setup to ensure you dont exeed any limits by figuring out at what temperautures and current limits the cell can hit said temperature limits.

i would never build a battery that runs that close to its limits unless its for something like drag racing and lifespan/saftey is secondary to performance.
Lithium beats liquid dinosaurs.

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Re: Li-ion cells cycle ageing

Post by john61ct » Feb 05 2020 9:57am

Of course I did not mean cells under say 60Ah.

And I have no expectation this will come to pass, but it might! no one can predict the future, mass market batteries already on the market with internal heating capability thermostatically controlled, so why not a sensor?

Just saying, it would be very useful to "more instantly" see the impact of various C-rates, peak or continuous on internal temperatures, without having to wait for the delta to dissipate until it is detectable from the outside.

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Re: Li-ion cells cycle ageing

Post by john61ct » Feb 05 2020 9:58am


flippy wrote:i would never build a battery that runs that close to its limits unless its for something like drag racing and lifespan/saftey is secondary to performance.
In my case I shoot for rates that create **no** temp rise detectable from the outside at all.


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flippy   1 MW

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Re: Li-ion cells cycle ageing

Post by flippy » Feb 05 2020 5:09pm

john61ct wrote:
Feb 05 2020 9:57am
Just saying, it would be very useful to "more instantly" see the impact of various C-rates, peak or continuous on internal temperatures, without having to wait for the delta to dissipate until it is detectable from the outside.
for the people that care about this its usually that those people have the knowledge, money and time to put in the work to map out a cell.
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spinningmagnets   100 GW

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Re: Li-ion cells cycle ageing

Post by spinningmagnets » Feb 05 2020 5:40pm

docware, thank you for posting this info. The heat that is generated by a given discharge is an interest of mine. I have the money, but I simply don't have the time to post the tests that I want to do. The world (and ES) is a better place because of data like this.

Image

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Re: Li-ion cells cycle ageing

Post by Dak77 » Feb 06 2020 12:03am

Wow. I knew colder temps raised the IR , but I had no idea how drastically each deg. affected it. Very good info . Does continued use at low temps cause permanent accelerated degredation? I mean, you are effectively operating the cells at an increasingly higher C rating with increasingly higher resistance as temps drop, correct?

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flippy   1 MW

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Re: Li-ion cells cycle ageing

Post by flippy » Feb 06 2020 4:51am

Dak77 wrote:
Feb 06 2020 12:03am
Wow. I knew colder temps raised the IR , but I had no idea how drastically each deg. affected it. Very good info . Does continued use at low temps cause permanent accelerated degredation? I mean, you are effectively operating the cells at an increasingly higher C rating with increasingly higher resistance as temps drop, correct?
tesla heats up the battery to nearly 50 in order to enable ludicrous mode/track mode.
otherwise it wont get up to the amps needed (nearly 1500A) without causing massive sag and uncontrolled heating of the cells.
it also does this if you drive to a supercharger it will try to heat the battery so it can accept the 150+kW of charge it can get.

so yes, a hot battery is a happy battery. to a certain point. unless you have spent millions in battery temperature managment i would just stick to ambient temps. going over 50 without thermal control is not a good idea.
Lithium beats liquid dinosaurs.

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Re: Li-ion cells cycle ageing

Post by docware » Feb 06 2020 5:52am

As flippy wrote, contrary to storage mode, in operation mode higher temperature above 30 °C
are better for Li-ion cells. Of course, lower temperatures bellow 15 °C mean worse operation conditions. All because temperature has significant impact on the chemical conversions, diffusion of the ions through the electrolyte, intercalation and deintercalation of the ions in the electrodes, …..

Want to remind that at our comparative cycling test are cells on friendly temperatures. In the real life is situation different. Not to speak about temperature differences between the cells at the battery wall and internal cells or temperature gradient through the cells itself.
LG M36 cycling - surface temperature.jpg
LG M36 cycling - surface temperature.jpg (176.19 KiB) Viewed 1592 times

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flippy   1 MW

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Re: Li-ion cells cycle ageing

Post by flippy » Feb 06 2020 7:12am

here is a view on capacity from a samsung 29E, the cell had a easy load so not much internal heating so it takes ambient temps changes quite well and thus bigger changes on capacity.
the difference was about 5c between heating and aircon. you see the wear as a constant but the big changes are from changes in ambient during the course of a day. the cell remained basically at ambient at all times.

Image


same time but much higher load, and lots of internal heating so the cell is much more even as the cell is constant ridden hard to keep the temperature up.

Image
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madin88   1 GW

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Re: Li-ion cells cycle ageing

Post by madin88 » Feb 06 2020 11:22am

Thats all very interesting thanks for sharing docware :thumb:

I have a small question, as LG seems to have so much better cycle life, couldn't it be because of the higher LVC?
LG was 4,1 - 3,4V, and all other down to 3,3V.

If find it quite surprising that if you use high current cells at very low discharge currents that cylce life is still worse as on high capacity cells.
I always had the meaning that they will live longer when used far below the specs but it seems not.

Does your equipment allow for a 5-10A cylce test, with something like 2A charge current? That would be nice to have and also a cylce test between 4,15V and 3,2V or so as comparison.

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Re: Li-ion cells cycle ageing

Post by docware » Feb 06 2020 12:19pm

Well, I again recommend to read all Pajda´s post for understanding the excelent result of LG M36 as also high power cells poor results.
LVC 3,4 V …... LG M36, Sanyo GA, LG MJ1, Samsung 50E, Samsung 35E
LVC 3,3 V ....... Panasonic PF, Samsung 29E, Samsung 30Q , SONY VTC6

Max. charging current is 5A, max. discharging current 10A.
Currently we are running tests at these particular conditions. Maybe in the future we can run test with higher loads. It is possible that after reading Pajda´s post no higher load testing will be required.

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Re: Li-ion cells cycle ageing

Post by madin88 » Feb 06 2020 12:51pm

OK thanks.
docware wrote:
Feb 06 2020 12:19pm
Currently we are running tests at these particular conditions.
Which cell at which conditions exactly?

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flippy   1 MW

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Re: Li-ion cells cycle ageing

Post by flippy » Feb 06 2020 12:57pm

madin88 wrote:
Feb 06 2020 11:22am
Does your equipment allow for a 5-10A cylce test, with something like 2A charge current? That would be nice to have and also a cylce test between 4,15V and 3,2V or so as comparison.
both docwares and my equipement can both do 10A i believe. but why would you do sustained testing beyond the official ratings of a cell? i dont know about docware but i like my test area not to be burned down.
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madin88   1 GW

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Re: Li-ion cells cycle ageing

Post by madin88 » Feb 06 2020 1:19pm

I was referring to high current cells like VTC6, HG2, 30Q where 5-10A discharge and 2A charge would be within specs of course.

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Re: Li-ion cells cycle ageing

Post by Pajda » Feb 06 2020 2:10pm

madin88 wrote:
Feb 06 2020 11:22am
I have a small question, as LG seems to have so much better cycle life, couldn't it be because of the higher LVC?
LG was 4,1 - 3,4V, and all other down to 3,3V.
Such small difference does not have significant impact on cycle life in SoC window below 70%.
madin88 wrote:
Feb 06 2020 11:22am
If find it quite surprising that if you use high current cells at very low discharge currents that cylce life is still worse as on high capacity cells.
I always had the meaning that they will live longer when used far below the specs but it seems not.
The principle of this issue was already formally described in this topic. So yes HP cells have significantly worse cycle life than most HE cells under low loads up to ca 1-2C continuous discharge. Generally(Although I do not like generalizations) HP cells cycle life is almost independent of the load. That means that HP cells should be used only in applications which really needs HP cells. From my point of view there are three fundamental categories of the cells on the market if we take a cycle life into account.

HE cells (up to 1C continuous) M36, MJ1, GA, 35E
"BP" (balanced parameters) cells (up to 3C continuous) 29E, M29
HP cells (more than 3C continuous) 30Q, HG2, VTC6

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Re: Li-ion cells cycle ageing

Post by Pedrodemio » Feb 06 2020 10:48pm

docware, thanks a lot for undertaking this endeavor, doing a whole lot of cell cycling tests is something I always wanted to do, but unfortunately I have no conditions at the moment or in the foreseeable future

One suggestion for the future of the tests

I’ve mainly build electrical skateboards, and a guy named Mathias Recalde Koller did a study where he gathered and bunch of logs from all over the world and built a standard riding cycle, very much like what is used to test consumption for bigger vehicles, I’m almost certain that someone must have done it for ebikes. If a discharge and charge curve is derived from a cycle like that, the cycling would be way more in line with real life use. It comes with a new set of challenges since the loading would vary with battery size, so a mean pack configuration would have to be determined

Maybe this doesn’t really change the results, probably Padja and others can share some knowledge if it’s a worth pursuit, also I don’t know if the tester you use would allow for a highly complex discharge curve

Find his paper on the link bellow

https://drive.google.com/file/d/1GMKLe- ... p=drivesdk

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Re: Li-ion cells cycle ageing

Post by john61ct » Feb 07 2020 3:16am


madin88 wrote:If find it quite surprising that if you use high current cells at very low discharge currents that cylce life is still worse as on high capacity cells
Low C-rates were the norm, lifespan and **energy** density the goals.

Then the market demanded higher **power** density, and the chemists have been tweaking formulations ever since.

Turns out there is an inherent conflict between the two, if you want huge C-rates capability and lighter weight you sacrifice Ah capacity and longevity.

So, only buy the power density you actually need if value for money is important to you.


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