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EDLC and Li-ion hybrid supercapacitors - claims that don't add up.

Discussion in 'General Electronics Discussion' started by Mr. Watts, Sep 9, 2019.

  1. Mr. Watts

    Mr. Watts

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    Sep 9, 2019
    I’ve been taking a look at lithium-ion super capacitors as an alternative to EDLC’s. The claim is that they have a much superior “specific energy” capability. Wikipedia quotes ‘specific energy’ as 11-14 Wh/kG, but then contradicts itself with 20 Wh/kG:

    “The packaged energy density of an LIC is approximately 20 Wh/kg, roughly four times higher than an EDLC ….. “

    One particular Japanese manufacturer claims 37 Wh/kG for their Li-ion supercap.

    Meanwhile the manufacturers of EDLC’s give the ‘energy density’ of their products as around 4-6 Wh/kG.

    Let’s see the numbers:

    1) A 100F/3volt EDLC supercap.

    Energy stored @ 3.0v = 0.5 X 100F X 3* = 450 Joules.

    Typical weight of component = 22 g.

    1 Joule = 2.78 x 10-4 Wh.

    Hence energy density is 450/22 = 20.45 J/g. = 20.45 X 2.78 X 10 -4 X 10 +3 = 5.685 Wh/kG

    Which agrees with that quoted by the manufacturers, depending on weight (which varies slightly with each manufacturer).

    2) Now the lithium-ion hybrid supercap.

    A 100F/3.8 volt Li-ion Supercap

    The good news: At 3.8 v, these have a higher voltage rating than EDLC’s.

    The bad news: They have a lower limit of 2.2 volts, below which de-intercalation takes place and is not recoverable. Therefore only 1.6 v is usable.
    Energy stored = 0.5 X 100F X (3.8*2 – 2.2*) = 480 Joules.

    Hardly any different from the EDLC type. Assuming the weights are similar – there’s nothing in it. Where is the “four times higher than an EDLC”? Am I missing something?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,228
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    Nov 17, 2011
    Energy is E = 1/2 * C * V² not 1/2 * C * V. However you somehow arrive at the correct value of 450 J o_O

    That should be E = 0.5*100F*(3.8V-2.2V)² = 128 J
    You need to sqaure the "useable" voltage.

    450J/128J = 3.5 which ties in nicely with
     
  3. Mr. Watts

    Mr. Watts

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    Sep 9, 2019
    1) My statement was copied & pasted from WORD and my "V squared" came out as V*, which is why my calculation of 450 Joules for the EDLC is correct. (I don't see an ability to write the squared function on this site).

    2) Your calculation for the energy stored in the Li ion supercapacitor is wrong. It should be 0.5 X 100 X (3.8 squared - 2.2 squared).J What you have "proved" using your incorrect calculation is exactly the OPPOSITE to the statement that Li ion supercapacitors have 4X the energy storage of EDLC's! Your unfinished sentence: "450J/128J = 3.5 which ties in nicely with......" shows you have misunderstood the entire premise.
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    9,228
    1,861
    Nov 17, 2011
    Key combination AltGr + 2 ?
    Or use the "sup" tags from the menu.
    Not unfinished, the following quote is meant to be part of the sentence - I admit that's not very obvious. Apart from grammatical issues, it seems I got that part wrong, however. Sorry for that. Maybe it was too early in the morning for me :(
     
  5. Mr. Watts

    Mr. Watts

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    Sep 9, 2019
    The "usable energy" stored in a capacitor has to be the number of Joules at the higher voltage, minus the number of Joules at the lower voltage. Hence: 0.5 X F X 3.8 (squared) less 2.2 (squared) J.
    P.S. No sign of a 'sup' tag.
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    9,228
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    Nov 17, 2011
    upload_2019-9-10_10-26-22.png
     
  7. Mr. Watts

    Mr. Watts

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    Sep 9, 2019
    Thanks, but that's bizarre. The sup tag only shows when you put the cursor in that area. Otherwise it's just a blank space, waiting to be discovered!
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    9,228
    1,861
    Nov 17, 2011
    Which browser do you use?
    I see the icon in Chrome, Internet Explorer 11, even in Edge.
     
  9. Mr. Watts

    Mr. Watts

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    Sep 9, 2019
    Maybe because I'm using Windows 7. Testing:- V2. Nope, doesn't work.V2.
     
  10. dave9

    dave9

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    Mar 5, 2017
    It has nothing to do with Win7, which I am currently using and see it on Firefox. It's all the browser.
     
  11. Mr. Watts

    Mr. Watts

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    Sep 9, 2019
  12. Alec_t

    Alec_t

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    Jul 7, 2015
    Sub/sup show ok in Firefox/ Win10.
     
  13. dave9

    dave9

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    Mar 5, 2017
    I just tried it on Chrome Version 76.0.3809.132 (Official Build) (64-bit) and supsup works, is always visible. Chrome updated itself while I was doing that, is now Version 77.0.3865.75 (Official Build) (64-bit) with no supsup change.

    You might try running Chrome in safe mode to see if you have some changes add-ons etc preventing it.
     
  14. Mr. Watts

    Mr. Watts

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    Sep 9, 2019
    Version 77.0.3865.75 (Official Build) (64-bit)
     
  15. Mr. Watts

    Mr. Watts

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    Sep 9, 2019
    Have updated Chrome to: Version 77.0.3865.75 (Official Build) (64-bit) as per your suggestion. Result: No difference - no sub/sup symbols.

    Don't think I'm going to try safe mode. Getting too complicated and way off track. I came here to pose a question on supercapacitors but am now getting bogged down in the minutiae of the internet/software/computers. Not my kettle of fish at all.
     
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