Li-ion cells cycle ageing

Batteries, Chargers, and Battery Management Systems.
electric_nz   100 W

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Re: Li-ion cells cycle ageing

Post by electric_nz » May 12 2020 2:40am

Very interesting to see the internal resistance of many of these remain consistently low over the full 700 cycles. It appears this new generation of cells (vtc6, hg2) has both high power, relatively high capacity and outstanding cycle life. Assuming these formulations are the same used in factory built electric vehicles; the future for electric propulsion looks very bright. Amazing work, thanks!

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madin88   1 GW

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Re: Li-ion cells cycle ageing

Post by madin88 » May 14 2020 6:19am

Centurio wrote:
May 09 2020 6:47am
But we have to consider, accoring the first post, the discharge current is 2.5A only. Yeah, its good over the datasheets discharge rate and closer to reality. But I think many e bike riders here load their batteries with higher constant current per cell. Or do you want to commute 30mph (45kmh) with a BBS02 750W assuming 25A consumption and carry a 14s10p (10p!!!) pack with you?
Yes it would be good to have another cylce test, with lets say:

5A for LG M36 and MJ1
5-10A for 29E7 and M29
10-15A for HG2 and VTC6 with 2A charge current or so

That would be way closer to how the cells usually being used in real world.

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Re: Li-ion cells cycle ageing

Post by Centurio » May 14 2020 6:33am

That would be way closer to how the cells usually being used in real world.
I was thinking the same. But: Why not to monitor a battery under realy conditions. Monitor the discharge, charge, cycle, ambient temperatur, celltemperatur (optional), ++. It sould be something easy, anyone can hook up his pack, analize and if desired, shere the data on ES.

Maybe little off topic. But anyway, maybe one knows a link.

Cephalotus   10 kW

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Re: Li-ion cells cycle ageing

Post by Cephalotus » May 14 2020 9:51am

madin88 wrote:
May 14 2020 6:19am


Yes it would be good to have another cylce test, with lets say:

5A for LG M36 and MJ1
5-10A for 29E7 and M29
10-15A for HG2 and VTC6 with 2A charge current or so

That would be way closer to how the cells usually being used in real world.
Typically the battery in an electric bike should/will last for 1-3 hours of continous riding. On average this translates to C/3 to 1C discharge rates. So 2,5A per cell is perfectly fine.

Who would build an ebike that has an empty battery after just 12 minutes of driving? (VTC6 or HG2 at 15A continous discharge)

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Re: Li-ion cells cycle ageing

Post by john61ct » May 14 2020 10:54am

The point is not the average

some use cases need peak currents, that may not last that long

to be many times the usual amps capacity

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Re: Li-ion cells cycle ageing

Post by docware » May 15 2020 4:22am

New data : Samsung 35E 673 cycles, Samsung 50E 650 cycles, LG HG2 658 cycles.
Samsung 35E  673 cycles.jpg
Samsung 35E 673 cycles.jpg (130.19 KiB) Viewed 2683 times
Samsung 50E  650 cycles.jpg
Samsung 50E 650 cycles.jpg (142.18 KiB) Viewed 2683 times
LG HG2  658 cycles.jpg
LG HG2 658 cycles.jpg (125.8 KiB) Viewed 2683 times
Capacity decay comparison  zoom offset 15.5.2020.jpg
Capacity decay comparison zoom offset 15.5.2020.jpg (134.7 KiB) Viewed 2683 times
DCIR comparison 15.5.2020.jpg
DCIR comparison 15.5.2020.jpg (102.71 KiB) Viewed 2683 times

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madin88   1 GW

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Re: Li-ion cells cycle ageing

Post by madin88 » May 15 2020 7:06am

Cephalotus wrote:
May 14 2020 9:51am
Typically the battery in an electric bike should/will last for 1-3 hours of continous riding. On average this translates to C/3 to 1C discharge rates. So 2,5A per cell is perfectly fine.

Who would build an ebike that has an empty battery after just 12 minutes of driving? (VTC6 or HG2 at 15A continous discharge)
You are right there. This is true for e-bikes most people ride with or the average one from the large companies.

If someone start building his own bike with tuneable controller, or when i think about E-mopeds like Surron, the peak C-rate usually is much higher there.
Surron as example has 6kW peak power and around 1900Wh battery (Panasonic PF) so already above 3C or 9A per cell. Still not true continuous in most cases but the controller allows it if you want. Thats the point.

The 2.5A tests are more a best case scenario and such 5, 10, 15A tests then would show the worst case and real lifetime then can be expected to be somewhere in between.

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Re: Li-ion cells cycle ageing

Post by john61ct » May 15 2020 8:20am

Note that most lifecycle testing is done at steady CC well below 0.4C

which most people here consider unrealistically low.

So yes using closer to 1C is better from that POV, if your usual usage is well below that then you're likely to get even longer lifespans.

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Re: Li-ion cells cycle ageing

Post by docware » May 15 2020 8:42am

madin88 wrote:
May 15 2020 7:06am
If someone start building his own bike with tuneable controller, or when i think about E-mopeds like Surron, the peak C-rate usually is much higher there.
Surron as example has 6kW peak power and around 1900Wh battery (Panasonic PF) so already above 3C or 9A per cell. Still not true continuous in most cases but the controller allows it if you want. Thats the point.

The 2.5A tests are more a best case scenario and such 5, 10, 15A tests then would show the worst case and real lifetime then can be expected to be somewhere in between.
Those are unrealistic expectations. Cells warming in the closed battery pack will be probably too high even for 5 A discharge continuous with significant temperature inhomogeneity of the cells. Without suitable thermal management of the pack we can expect faster degradation of the cells.

viewtopic.php?f=14&t=96360&p=1447905#p1447905

viewtopic.php?f=14&t=99047&p=1452025#p1452025
Samsung 30Q 2A v 5A.jpg
Samsung 30Q 2A v 5A.jpg (29.76 KiB) Viewed 2653 times
LG HG2 2A v 5A.jpg
LG HG2 2A v 5A.jpg (28.91 KiB) Viewed 2653 times

docware   1 kW

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Re: Li-ion cells cycle ageing

Post by docware » May 24 2020 6:20am

The final batch of data - Samsung 35E, 50E and LG HG2 finished 700 cycles.
Samsung 35E  700 cycles.jpg
Samsung 35E 700 cycles.jpg (130.47 KiB) Viewed 2533 times
Samsung 50E  700 cycles.jpg
Samsung 50E 700 cycles.jpg (143.17 KiB) Viewed 2533 times
LG HG2  700 cycles.jpg
LG HG2 700 cycles.jpg (126.4 KiB) Viewed 2533 times
Capacity decay comparison  zoom offset 24.5.2020.jpg
Capacity decay comparison zoom offset 24.5.2020.jpg (135.44 KiB) Viewed 2533 times
DCIR comparison 24.5.2020.jpg
DCIR comparison 24.5.2020.jpg (103.02 KiB) Viewed 2533 times
Just as a matter of interest, here is capacity decay comparison without Samsung 50E offset :
Capacity decay comparison  zoom   24.5.2020.jpg
Capacity decay comparison zoom 24.5.2020.jpg (134.59 KiB) Viewed 2533 times
Capacity decay comparison without zoom :
Capacity decay comparison    24.5.2020.jpg
Capacity decay comparison 24.5.2020.jpg (144.06 KiB) Viewed 2533 times

Pajda   1 kW

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Re: Li-ion cells cycle ageing

Post by Pajda » May 24 2020 7:48am

Should I ask for DCIR rise comparison in % without zoom? :)

docware   1 kW

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Re: Li-ion cells cycle ageing

Post by docware » May 24 2020 9:19am

Sunday afternoon, no brain capacity for such work :)
But have something better, source Excel file :
DCIR rise Excel file.xlsx
(16.15 KiB) Downloaded 87 times
Edit - DCIR without zoom :
DCIR without zoom.jpg
DCIR without zoom.jpg (109.88 KiB) Viewed 1268 times
Last edited by docware on Nov 14 2020 4:50am, edited 1 time in total.

Cephalotus   10 kW

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Re: Li-ion cells cycle ageing

Post by Cephalotus » May 24 2020 1:15pm

Hey,

very cool. Thank you.

Do you have cycle 1 vs cycle 700 charts for capacity and Ri for the HG2 cells?

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Re: Li-ion cells cycle ageing

Post by docware » May 24 2020 2:13pm

Currently preparing charts for all three cells.

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Re: Li-ion cells cycle ageing

Post by docware » May 25 2020 3:15pm

Samsung 35E has 87,4 % of initial capacity in the cycling interval 4,1 - 3,4 V / 2,5 A discharge. In standard range 4,2 - 2,5 V at 1 A discharge has 93,6 % of initial capacity and 93,6 % of initial energy.
Samsung 35E No2 after 700 cycles 4,2 - 2,5 V  1 A disch comparison.jpg
Samsung 35E No2 after 700 cycles 4,2 - 2,5 V 1 A disch comparison.jpg (144.78 KiB) Viewed 2338 times
Samsung 35E DCIR after 700 cycles.jpg
Samsung 35E DCIR after 700 cycles.jpg (104.04 KiB) Viewed 2338 times
Samsung 50E has 93,8 % of initial capacity (offset variant) in the cycling interval 4,1 - 3,4 V / 3,75 A discharge. In standard range 4,2 - 2,5 V at 1,5 A discharge has 95,7 % of initial capacity and 95,8 % of initial energy.
Samsung 50E No2 after 700 cycles 4,2 - 2,5 V  1,5 A disch comparison.jpg
Samsung 50E No2 after 700 cycles 4,2 - 2,5 V 1,5 A disch comparison.jpg (138.6 KiB) Viewed 2338 times
Samsung 50E DCIR after 700 cycles.jpg
Samsung 50E DCIR after 700 cycles.jpg (102.86 KiB) Viewed 2338 times
LG HG2 has 92,1 % of initial capacity in the cycling interval 4,1 - 3,3 V / 2,5 A discharge. In standard range 4,2 - 2,5 V at 1 A discharge has 94,7 % of initial capacity and 95,1 of initial energy.
LG HG2 No2 after 700 cycles 4,2 - 2,5 V  1 A disch comparison.jpg
LG HG2 No2 after 700 cycles 4,2 - 2,5 V 1 A disch comparison.jpg (120.38 KiB) Viewed 2338 times
LG HG2 DCIR after 700 cycles.jpg
LG HG2 DCIR after 700 cycles.jpg (104.31 KiB) Viewed 2338 times
Updated SOC comparative chart after 700 cycles :
SOC % versus voltage after 700 cycles.jpg
SOC % versus voltage after 700 cycles.jpg (291.58 KiB) Viewed 2338 times
Want to again remind that this was not comprehensive testing but only laboratory comparative testing of cycle aging at particular conditions. Conditions quite favourable to the cells, but on the other hand typical for lot of ebikes. However, in the real life there are other factors affecting the cells degradation, not only cycle aging.
Any opinions, comments, remarks ?

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Re: Li-ion cells cycle ageing

Post by john61ct » May 25 2020 6:37pm

Thank you.

I have to say even the lower-performing cells did pretty darn well. . .

Cephalotus   10 kW

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Re: Li-ion cells cycle ageing

Post by Cephalotus » May 26 2020 4:02am

Very good and very helpful.

Thank you very much!

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Honk   100 W

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Re: Li-ion cells cycle ageing

Post by Honk » Jun 05 2020 4:26pm

Now that you have confirmed cell performance at modest cycling then perhaps it's time for a more brutal approach.
E'g full 4.2V charging at high currents and high discharge rate down to 3V to simulate how folks tend to build their light weight packs and kind of abuse them hard.
It could be fun to see which cells that can keep up without to much damage!
Efficiency is king!

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Re: Li-ion cells cycle ageing

Post by mighty82 » Jun 16 2020 4:23pm

I would also like to see at least some of the cells tested at 4.2v. With this much great information it is a golden opportunity to see what difference 4.1v vs 4.2v actually makes with the other parameters being the same.

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serious_sam   10 kW

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Re: Li-ion cells cycle ageing

Post by serious_sam » Jun 16 2020 8:15pm

Honk wrote:
Jun 05 2020 4:26pm
mighty82 wrote:
Jun 16 2020 4:23pm
How much are you guys paying docware for performing all this extra testing at your request? Just curious.

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Honk   100 W

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Re: Li-ion cells cycle ageing

Post by Honk » Jun 17 2020 2:32am

Zilch - so I don't expect or demand anything from him.
It was just some basic curiosity from my side.
A few promising cells could be selected to narrow the effort.
And it might interest docware himself, based on curiosity!
Efficiency is king!

john61ct   100 GW

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Re: Li-ion cells cycle ageing

Post by john61ct » Jun 17 2020 8:54am

I agree such requests appear entitled.

It really is not that hard to start doing your own tests if you want to.

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Re: Li-ion cells cycle ageing

Post by mighty82 » Jun 19 2020 9:15am

Sharing ideas for future tests is not being entitled. I'm sure he's going to continue testing cells in the future anyway.

The effort put in here as well as the execution is amazing, and I am very grateful for it!

Having this many different cells tested at the same time is gold. Comparing cells tested at different times, by different people with different equipment is impossible.

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Re: Li-ion cells cycle ageing

Post by mighty82 » Jun 20 2020 11:36am

Any idea why the cells have lost more capacity percentage wise inside the cycling interval than total capacity degradation? Have you tried retesting the cells with the previous parameters after it has been fully cycled to see if some of the capacity within the cycling interval has been regained? Might be a posibility since they also regained capacity during a resting period as you mentioned :)

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Re: Li-ion cells cycle ageing

Post by docware » Jun 21 2020 10:21am

mighty82 wrote:
Jun 19 2020 9:15am
I'm sure he's going to continue testing cells in the future anyway.
Very probably not, cells testing became boring. Vegetable growing is much more interesting and enjoyable. :)
1.jpg
1.jpg (286.85 KiB) Viewed 1871 times
3.jpg
3.jpg (234.86 KiB) Viewed 1871 times
Comparing cells tested at different times, by different people with different equipment is impossible.
Wrong, it´s not easy, however it´s possible.
Any idea why the cells have lost more capacity percentage wise inside the cycling interval than total capacity degradation?
No.
Have you tried retesting the cells with the previous parameters after it has been fully cycled to see if some of the capacity within the cycling interval has been regained?
No.

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