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Author: Ville-Matias Heikkila <viznut@low.fi>
Date: Sat, 25 Jun 2022 14:38:42 +0300
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+A **supercapacitor** or an **ultracapacitor** is a capacitor with
+characteristics between ordinary (electrolytic) capacitors and rechargeable
+batteries.
+
+In comparison to batteries, supercapacitors
+
+* store less energy per mass (Li-ion batteries have about 10 to 100 times the energy density)
+* charge and discharge faster (up to 10 W/g vs up to 1.5 W/g for Li-ion batteries)
+* can be recharged up to a million times (vs 10000 times for Li-ion)
+* have longer lifespans (Wikipedia lists 5-10 years of working time in room temperatures vs 3-5 years for Li-ion batteries, but Sutherland casually states "last decades")
+* can be manufactured with non-specialized equipment without exotic materials
+
+Making
+------
+
+There are many DIY guides for supercapacitors online. They have usually
+chosen activated carbon for the electrode material, and this is likely the
+simplest and "greenest" approach. The online guides also usually use
+commercial intermediate products instead of deriving everything from natural
+resources.
+
+Materials typically listed:
+
+* Activated carbon: Made of charcoal or coal by e.g. heating it for 1 h in a muffle furnace at 450 °C in the presence of air. The commercially available activated carbon usually comes from the burning of coconut husks, but other organic sources may also be used.
+* Manganese dioxide (MnO2): Occurs naturally in certain minerals but needs to be purified at least for electrolytic battery use. This involves dissolving the raw material in sulfuric acid. Manganese is also found in organic life and is an essential dietary element for humans.
+* Iron
+* Water
+* Salt
+
+See also
+--------
+
+* [Strategies of Degrowth Computing (Brian Sutherland, Limits'22)](https://computingwithinlimits.org/2022/papers/limits22-final-Sutherland.pdf) discusses a [[Raspberry Pi]] workstation project that uses supercapacitors for solar storage.
