Measure the volume change of a battery cell

Question

Hello,

I would like measure the volume change of a lithium ion pouch cell during charge and discharge. The volume change will mainly reflect on the thickness of the battery. When it is discharged it is about 7 mm and it will increase by about 10% when it is charged. I would like to track the changes during charging.

We find this component as below which is a linear motion potentiaometer. https://se.farnell.com/ab-elektronik/4114902470/sensor-linear-5-kohm-20-flange/dp/2311430

±20% Selection tolerance
± 2.0% Typical independent linearity
10mm ± 0.5mm Effective travel

Does the 20% means the accuracy of the potentiometer?

Do you have any suggestions about other type of sensors that I could use for this kind of measurement?

Thanks a lot for the help!

Best Regards,

/Zeyang

shabaz · Accepted Answer

Hi Zeyang,

I think you're right, it is likely the overall resistance tolerance. But I think the 750 gram needed to operate this sensor could be too high for your application maybe? I don't know how much force is allowed. I think I'd do it differently. There are many ways you could consider. If money was not a concern, then an electronic dial indicator could be used, because that is available in low force versions, and it will be already calibrated. It can have a digital output to your computer, although an interface could be needed. For example, see Mitotoyu products.

Otherwise, at very low cost (but you would need to do some machining and your own calibration) you could consider inductive sensing, e.g. see here:

Getting Started with the LDC1000 - Small Metal Detection!

You could have the metal plate target spaced off the battery using (say) a plastic block, so that the metal of the battery is not part of the inductive sensing.

For calibration, you could use some manual measurement or reference devices, e.g. calipers or a gauge, or reference thickness blocks aka parallels (expensive) or layers of sheet material (cheap, less accurate but maybe sufficient for your needs).

I think the lowest cost (and easiest) could be to use electronic calipers and just measure manually at different intervals during the charge/discharge process. But many have a serial output, so you could rig something up to automate this.

michaelkellett · Answer

You could do the measuring with Mitutoyo 575123 (Farnell 1667327 £169) - it outputs data in Mitotyo format so you need an interface and neither Farnell nor RS seem to sell these ! You can buy the interface from: https://gb-greatgages.glopalstore.com/search?type=product&q=Mitutoyo+USB+Data+Input+Tool And they also sell a range of other displacement gauges and interfaces, as Shabaz suggested pick low force one - I seem to remember that you can remove the springs from some of the Mititoyo ones. MK

dougw · Answer

You could also try capacitance measurement. If you put a foil "plate" on the battery and measure the capacitance to a nearby metal plate, the distance between plates will be directly proportional to the capacitance. See this road test for a circuit (and software) that could work for this small change in distance: Texas Instruments FDC2214 Capacitance to Digital - Review

jw0752 · Answer

Hi Shabaz,

As soon as I read Zeyang's question I thought about the LDC1000 that you introduced to us a while back. Here is perhaps a good application. It is good you remembered it as I might have had a bit of trouble finding it.

John

mcb1 · Answer

When it is discharged it is about 7 mm and it will increase by about 10% when it is charged. I would like to track the changes during charging. From this information it seems you're trying to to detect a 0.7mm change in size. Is this simply an experiment or is it some form of 'fully charged' detection device, as the options available vary considerably. I'm not sure that this method is a wise or safe method for detecting when a Lithium based battery is charged. Yes they do swell, but it may not be the same across all batteries. For an experiment, leverage will give you a much greater change which may be easier to detect. eg a 3:1 ratio will change the 0.7mm to 2.1mm. The alternative is a fixed plate and some form of measuring scale underneath. As the pack swells it will exert a force onto the load cell, which you may be able to translate to a reading when it reaches 7.7mm height. The only issue I see is what if it swells unevenly, ie not just in height. Assuming it is a volume change, then suspension in water and the capacitive effect might be an option (see dougw experiment to measure fuel volume) Mark

genebren · Answer

Another approach would be to use a raspberry pI module with a camera to visually track the change in size. Or maybe you could us a loadcell next to battery in a confined space to measure the change in pressure as the battery swells. Gene

Measure the volume change of a battery cell

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