18650 Ragone Plot

[Battery Guy]

Greetings Everyone,

If you are unfamiliar with Ragone Plots, you may want to read this thread.

Here is the start of a Ragone plot for 18650 cells:

Please note that the Sony US18650VT cell was harvested from a Bosch power tool pack, and the A123 APR18650M1 was harvested from a DeWalt power tool pack.

If you are interested in which power tool battery packs have specific cells, see here.

Obviously this is a work in progress. I will post updates as they come in.

Cheers,
Battery Guy

 

[flashfiend]

Cool. Do you happen to have any AW IMR18650 cells to test?

 

[Battery Guy]

Cool. Do you happen to have any AW IMR18650 cells to test?

No, but I did test the AW AA cells. See my AA Ragone Plot thread.

I would be happy to add the AW IMR18650 cells. Just be aware that I probably won't have a chance to do any more testing for a couple of weeks.

Cheers,
Battery Guy

 

[jasonck08]

Battery Guy,

Do you have any equipment that would easily allow you to cycle a cell 50-100 times to test the longevity of the cell?

 

[Battery Guy]

Battery Guy,

Do you have any equipment that would easily allow you to cycle a cell 50-100 times to test the longevity of the cell?

Yes, I have equipment that will cycle cells. What the results of this type of testing will tell you about longevity is a matter of serious debate.

If you have a particular test in mind that would be of general interest to other CPF members, then I would be happy to run it for you and post the results. However, be forewarned that I am a bit backlogged and would like to finish the AA Ragone plots and 18650 Ragone plots before taking on any new pro bono work for the forum.

So, with that being said, what do you have in mind?

Cheers,
Battery Guy

 

[jasonck08]

I'd basically want to see some testing done with different types and brands of 18650's. For example: TrustFires, UltraFires, AW's, Sanyo's, Panasonics etc. I'd be willing to donate a few cells to the cause.

I noticed your PM's are off. Can you turn them on, or drop me an email at jasonck08 (AT) yahoo dot com.

 

[Battery Guy]

I'd basically want to see some testing done with different types and brands of 18650's. For example: TrustFires, UltraFires, AW's, Sanyo's, Panasonics etc.

I could add cycle life testing to the cells that I am using for the Ragone plot tests. I plan on adding TrustFires, UltraFires and AW cells to the tests. Which Panasonics were you thinking of?

Given that I need to finish up the AA Ragone plot and still have a lot to do on the 18650 Ragone plot, it may be awhile before I can get to the cycle life study.

What were you thinking for charge/discharge parameters? I propose the following:

Charge: C/2 to 4.2V (unless otherwise specified by the manufacturer); CV at 4.2V to C/50 current cut-off
Rest: 10 minutes
Discharge: 1.6C to 3V (unless otherwise specified by the manufacturer)
Rest: 10 minutes
Rinse and repeat

I know that the 1.6C seems a bit arbitrary, but it comes from the fact that I am limited to a current of 5A per channel on my system. I can combine channels to give higher current capability, but then I lose available channels. Given that some 18650 cells are up to 3Ah capacity, a 5A discharge corresponds to 1.67C.

The protocol would take about 4 hours per charge/discharge cycle, so 6 cycles per day, 42 cycles per week. I could speed things up for lower capacity cells by going to a fixed 5A discharge for all cells, rather than a fixed C-rate.

Let me know what you think.

Cheers,
Battery Guy

 

[jasonck08]

In addition to the TrustFires and UltraFires and AW's I was thinking about testing some Sanyo 2600 and Panasonic 2900 cells (maybe a couple other brands like Samsung and LG if I can get my hands on some).

Also the cutoff voltage for most Li-ion cells as specified by the manufacturer is 2.75v. The Panasonic 2900's go down to 2.5v. If you're discharging at a high C rate, then discharging completely to 2.5v for the Panasonic as opposed to the 3v mark will yield about 500mah more capacity.

I would recommend sticking at about a fixed 3A discharge rate. A fixed 5A is pretty tough on cells, especially cheaper ones with higher IR.

Also, I'd say do a initial discharge graph of all cells at the specified current (3A for example) when they are new, then do subsequent graphs at 25, 50, 75, 100 etc.

That way we can visualize how the capacity of various cells drops over time, and perhaps how the increased of the cells IR causes more voltage drop over the test as the cell ages.

Let me know what you think!