Tabless design cylindrical cells tests

CamLight said:
Excellent! Has to be some reason to avoid the weld areas though or otherwise the manufacturers wouldn’t have these warnings. Hopefully she/he can give you some great info!

Do you also have access to an applications or test engineer? They’d be the ones who test production cells and/or get the feedback from customers. The cell development labs are often dealing with just coin and pouch test cells
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That is indeed correct. She's someone who worked on cylindrical cell system design optimization, so she's likely an excellent source on the subject.
 
riba2233 said:
knowing my luck it would happen two weeks after I got them and they would be even cheaper lol
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I kind of feel this way about buying lithium RN.
Seems that we are experiencing a boom of improvements in batteries, reminds me of the early 2010's lately;

I could probably get my hands on some M58T and build the high density battery of the future, but it feels like i'm buying a Sega Dreamcast right before the Playstation 2 came out.
 
neptronix said:
I kind of feel this way about buying lithium RN.
Seems that we are experiencing a boom of improvements in batteries, reminds me of the early 2010's lately;

I could probably get my hands on some M58T and build the high density battery of the future, but it feels like i'm buying a Sega Dreamcast right before the Playstation 2 came out.
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I wouldn't even touch any high cost low power density cells nowadays.

All these innovations like high Si anodes, lithium sulfur cathodes, graphene-oxide coated tabs (yes, it's actually a thing to greatly reduce bonding resistance between the electrode material and tab), tabless cylindrical cells, aluminium-ion cathodes, etc., are making buying today's cells difficult on my end if I'm looking for high energy + high power.
 
Pajda said:
- EVE 40PL started 0.5C-5C @ 4.20-2.80V (to check if the poor cycle life is related with the DoD)
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I just had a client cancel some testing so I thought this would be a good time to try to help figure out why our EVE 40PL cycling results were so different. Our low voltage cutoffs and charge rates were different (leading to different actual voltage cutoffs) but the IR of this cell is so low I’m just not convinced the small differences in our cutoffs (in terms of actual SOC) could lead to such large differences in cycle life. But I’ve been surprised by cell behavior before so it’s time to test!

I’m starting 100 cycles of an EVE40PL at 2A charge to 200mA/10min rest/20A discharge to 2.50V/20 min rest to (fairly closely) emulate what you did when you got those short cycle life results. I’ll post in this thread when done.

(edit) Wondering if going down to 8A discharge might be even better to better help flesh out if true DOD matters enough to create our different results?
 
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small update in the first post Tabless design cylindrical cells tests

News:
- BTCAP 40P added in 5C and 10C discharge voltage drop charts. Not great, not terrible :) . This cell holds the voltage almost to the end and can deliver its rated capacity even at 10C. Unfortunately, this is not much useful feature for practical life.

Update:
- added more cycles for almost all charts
- added first 100 cycles for BAK 45D at 3C-3C test, this cell is just awesome.
 
CamLight said:
I just had a client cancel some testing so I thought this would be a good time to try to help figure out why our EVE 40PL cycling results were so different. Our low voltage cutoffs and charge rates were different (leading to different actual voltage cutoffs) but the IR of this cell is so low I’m just not convinced the small differences in our cutoffs (in terms of actual SOC) could lead to such large differences in cycle life. But I’ve been surprised by cell behavior before so it’s time to test!

I’m starting 100 cycles of an EVE40PL at 2A charge to 200mA/10min rest/20A discharge to 2.50V/20 min rest to (fairly closely) emulate what you did when you got those short cycle life results. I’ll post in this thread when done.

(edit) Wondering if going down to 8A discharge might be even better to better help flesh out if true DOD matters enough to create our different results?
Click to expand...
Yes, reducing the discharge current will lead to increase of the DoD and thus the expected result should be seen sooner. Actually, this can be seen in my other test of 3C-3C with 2.5 V cut-off, where EVE 40PL loses capacity right from the start and is completely weared within 100 cycles. From the results of other competitors, 3C fast charging should not be a problem. By the way, I should also retest this with the 2.8 V cut-off for the EVE 40PL in the future.

My actual results at 150 cycles for the EVE 40PL are that lowering the DoD to 2.8 V (yellow) had a significant effect on lifetime. Unfortunately, the sample with 2.5V cut-off without welding (pink) is now only approaching the first 50 cycles, where the breaking point should occur somewhere around the 70th. So I need at least 10 more days to get there.

and the difference in temperature on the cell surface between the current drain through the welded Cu strips and the BF-2A holder is about 6-8 °C.
 
Pajda said:
Yes, reducing the discharge current will lead to increase of the DoD and thus the expected result should be seen sooner. Actually, this can be seen in my other test of 3C-3C with 2.5 V cut-off, where EVE 40PL loses capacity right from the start and is completely weared within 100 cycles. From the results of other competitors, 3C fast charging should not be a problem. By the way, I should also retest this with the 2.8 V cut-off for the EVE 40PL in the future.

<snjp>

and the difference in temperature on the cell surface between the current drain through the welded Cu strips and the BF-2A holder is about 6-8 °C.
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Thanks for the info!
I’m surprised the temp difference was that large…interesting!

Great to hear that fast charging didn’t affect the results. I’ll switch to 5A charge/8A discharge (still 2.50V cutoff) then as I’d like to speed up the cycling. This will mean that I am using the same charge current as my previous testing but just slowing down the discharge. Ten minute rests.
 
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Yeah, we're at the point where cell anodes, electrolytes and interconnects are good enough to allow fast charging without active thermal management (heating/cooling).
 
What are people finding the best option of weld these high power cells? It order to use the amps with out overheating the busbars, you would need at least 0.5 mm Ni plated Copper busbars vs the "normal" <0.3mm.
 
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