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A prototypical capacitor consists of two electrodes in parallel separated by a nonconducting dielectric material. What is the difference between a conventional capacitor and a supercapacitor?

It seems that conventional capacitors usually have solid dielectric materials, like polymer films, ceramics, or glass. But is this always the case? (I guess one possible exception is an electrolytic capacitor, such as an aluminum electrolytic capacitor. But in that case, it seems that it is an electrode that may be in the liquid phase, and not necessarily the dielectric separating the electrodes.)

Supercapacitors are more technically known as electric double layer capacitors (EDLCs). An electric double layer forms at the interface of the electrode and the dielectric. It seems that in a supercapacitor, the dielectric is usually a liquid. But is this always the case?

Can it be said that the difference between a conventional capacitor and a supercapacitor is that

  • a conventional capacitor has a solid dielectric, whereas
  • a supercapacitor has a liquid dielectric?

I would appreciate it if anyone could share an academic resource -- book or journal article -- that explicitly states the difference.

Incidentally, the journal article here (Olabi, Energy, 2021) states:

Due to solid dielectric between the electrodes, supercapacitors store energy by means of an electrolyte solution between two solid conductors.

I wonder if they made a typo in that sentence.

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  • \$\begingroup\$ The difference between the two is more of functional than structural. \$\endgroup\$ – Eugene Sh. Dec 10 '20 at 23:04
  • \$\begingroup\$ Regular electrolytics use liquid electrolyte too. In that case the dielectric is "anodized" oxidation layer on one of the conductor films. \$\endgroup\$ – user_1818839 Dec 10 '20 at 23:18
  • \$\begingroup\$ Supercapacitors wear a cape. \$\endgroup\$ – Elliot Alderson Dec 10 '20 at 23:22
  • \$\begingroup\$ A supercap is almost a cross between a rechargable battery and a capacitor, \$\endgroup\$ – Neil_UK Dec 10 '20 at 23:29
  • \$\begingroup\$ en.wikipedia.org/wiki/Supercapacitor any help? \$\endgroup\$ – Finbarr Dec 11 '20 at 0:45
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In an electrolytic capacitor, the capacitance is in the insulating material between the electrolyte and the metal, normally a metallic oxide.

A supercap is a kind of electric cell, a battery. It works by ionic migration and redox reactions. The amount of migration required is just electrical alignment, and the redox reactions are just with adjacent molecules, so speed is fast (for a battery) and charge storage is low (for a battery).

A double-layer super-cap has a bound charge layer protecting one electrode, so the battery is in series with a single-molecule-thick capacitor. This very thin capacitor has very high capacitance, because it is so thin.

The liquid electrolyte doesn't have to be liquid by any other measure at all: it just has to be liquid enough to allow the formation of the bound charge layer, possibly rotational ionic migration, and possibly adjacent redox reactions.

The picture you linked to, showing electrodes separated by a electrolyte and separator, does not show a solid dielectric. They've perhaps had a brain freeze and misunderstood the mechanical separation of the two electrodes as being something else.

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