Better Capacitors Through Nanotechnology

Traditionally, capacitors are like really bad rechargeable batteries. Supercapacitors changed that, making it practical to use a fast-charging capacitor in place of rechargeable batteries. However, supercapacitors work in a different way than conventional (dielectric) capacitors. They use either an electrostatic scheme to achieve very close separation of charge (as little as 0.3 nanometers) or electrochemical pseudocapacitance (or sometime a combination of those methods).

In a conventional capacitor the two electrodes are as close together as practical and as large as practical because the capacitance goes up with surface area and down with distance between the plates. Unfortunately, for high-performance energy storage, capacitors (of the conventional kind) have a problem: you can get high capacitance or high breakdown voltage, but not both. That’s intuitive since getting the plates closer makes for higher capacitance but also makes the dielectric more likely to break down as the electric field inside the capacitor becomes higher with both voltage and closer plate spacing (the electric field, E, is equal to the voltage divided by the plate spacing).

[Guowen Meng] and others from several Chinese and US universities recently published a paper in the journal Science Advances that offers a way around this problem. By using a 3D carbon nanotube electrode, they can improve a dielectric capacitor to perform nearly as well as a supercapacitor (they are claiming 2Wh/kg energy density in their device).

cap1The capacitor forms in a nanoporous membrane of anodic aluminum oxide. The pores do not go all the way through, but stop short, forming a barrier layer at the bottom of each pore. Some of the pores go through the material in one direction, and the rest go through in the other direction. The researchers deposited nanotubes in the pores and these tubes form the plates of the capacitor (see picture, right). The result is a capacitor with a high-capacity (due to the large surface area) but with an enhanced breakdown voltage thanks to the uniform pore walls.

cap2To improve performance, the pores in the aluminum oxide are formed so that one large pore pointing in one direction is surrounded by six smaller pores going in the other direction (see picture to left). In this configuration, the capacitance in a 1 micron thick membrane could be as high as 9.8 microfarads per square centimeter.

For comparison, most high-value conventional capacitors are electrolytic and use two different plates: a plate of metallic foil and a semi-liquid electrolyte.  You can even make one of these at home, if you are so inclined (see video below).

We’ve talked about supercapacitors before (even homebrew ones), and this technology could make high capacitance devices even better. We’ve also talked about graphene supercaps you can build yourself with a DVD burner.

It is amazing to think how a new technology like carbon nanotubes can make something as old and simple as a capacitor better. You have to wonder what other improvements will come as we understand these new materials even better.

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Hackaday Links: November 2, 2014

Russians blowing up capacitors! As we all know, electronics only work because of blue smoke. [kreosan] is releasing this blue smoke from a few hundred caps. Fun times, even if they are a large number of inert tube shields in their collection of caps.

[mayhugh1] over on the home model engine machinist forum has built an 18 cylinder radial engine. It’s based on the Hodgson 9-cylinder radial engine that has been around for a while. The crank case is machined from a 5″ diameter rod of aluminum. There’s a Picassa album of the engine being constructed as well.

[Richard] wanted a Minecraft server, but not just any Minecraft server; this one demanded a custom case. A grass block was the inspiration, acrylic the medium, and a quad-core Mini-ITX the guts of the project.

Halloween was last Friday, and as always the tip line filled up with costume builds. [Leif] built a Ghostbusters costume complete with Muon trap, [Jeff] printed out some steampunk post-apocolyptic goggles, and [Green Gentleman] made a death-a-corn, although we’re struggling to figure out why the last one isn’t called an acorn-‘o-lantern.

[Matthias Wandel], a.k.a. the dude,  is well-known in certain circles for being a wizard of wood. One of the first projects that put him on the map was a pantorouter – a router to cut mortises and tenons. He’s going back to his roots and building a bigger version. This version uses models of routers that are available outside North America, and in the latest video [Matthias] has it dialed in very well.

The Open Source Remote Control was an entry for The Hackaday Prize that didn’t make the final cut. It’s now an indiegogo project, and has some really cool tech we can’t wait to see in mainstream RC transmitters.

Ask Hackaday: Graphene Capacitors On Kickstarter

Last week, we heard of an interesting Kickstarter that puts a capacitor and charging circuit in the same space as a AA battery. This is usually a very simple endeavour, but this capacitor has the same energy density as an alkaline cell. The chemistry inside this capacitor was initially attributed to lithium ion, and a few people in the comments section were wondering how this was possible. The math just didn’t seem to add up.

The guy behind this Kickstarter, [Shawn West], recently spilled the beans on these… interesting capacitors. Apparently, they’re not lithium ion capacitors at all, but graphene capacitors. Graphene capacitors you can buy. On Kickstarter. Graphene capacitors, also known as the thing that will change everything from smartphones to electric vehicles, and everything in between. I will admit I am skeptical of this Kickstarter.

Apparently, these graphene supercaps are in part designed and manufactured by [Shawn] himself. He fabricates the graphene by putting graphite powder in a ball mill for a day, adding a bit of water and surfactant, then running the ball mill for another few days. The graphene then floats to the top where it is skimmed off and applied to a nonconductive film.

There’s absolutely nothing that flies in the face of the laws of physics when it comes to graphene capacitors – we’ve seen a few researchers at UCLA figure out how to make a graphene supercap. The general consensus when it comes to graphene supercaps is something along the lines of, ‘yeah, it’ll be awesome, in 10 years or so.’ I don’t think anyone thought the first graphene capacitors would be available through Kickstarter, though.

I’m a little torn on this one. On one hand, graphene supercaps, now. On the other hand, graphene supercaps on Kickstarter. I’m not calling this a scam, but if [Shawn]’s caps are legit, you would think huge companies and governments would be breaking down his door to sign licensing agreements.

Post your thoughts below.

Roll your own capacitors


Rolling your own electronics components can be fun, but can also help in explaining how certain items actually work. [Addie] from The Toymakers recently set off to figure out how capacitors work, by making her own.

She understood the general concept behind capacitors and how they are constructed, but she wanted to see how it was done first-hand. To construct her capacitor, she selected aluminum foil as her conductor, and saran wrap as the dielectric. She admits that her first attempt was a failure, but undaunted, she carried on. Friends suggested that her conductors were a bit too small to hold any reasonable charge, so she tried larger sheets of aluminum foil to no avail.

She kept at it and found success after using several feet of foil to construct her capacitor. She charged it with a handful of AA batteries and was excited to see her multimeter come to life when she touched the leads to the cap.

While you likely wouldn’t use a hand-made capacitor in your next build, it is a fun experiment to do with children interested in learning about electronics.

[via Adafruit blog]

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Building air variable capacitors

In keeping with our opinion that radio operators were the original electronic hackers here’s a guide to building your own transmitting air variable capacitors. Using some roof flashing, Plexiglas, and various fasteners [David Hammack] was able to make it work. It’s not a perfect solution but he has some ideas to make the next one better. Give this a try after you’re done tweaking your crystals and building input devices.

[Thanks Rich]

Parts: 0.1uF decoupling capacitors

Most ICs need to be decoupled from their power supply, usually with a 0.1uF capacitor between each power pin and ground. Decoupling is usually used to remove noise and to smooth power fluctuations. Every project will need a few decoupling capacitors; our mini web server project has three ICs that require a total of 11. This can be an expensive part to buy in singles, so it’s crucial to stock up online. Read more about our favorite bulk through-hole and surface mount decoupling capacitors after the break. Continue reading “Parts: 0.1uF decoupling capacitors”

24kJ Capacitor Bank

The Leyden jar capacitor posted the other day fails to compare to what [FastMHz], one of the members over at the forums, has been busy building, a 24kj capacitor discharge bank. This capacitor bank will be configured for 4500v @ 2400uF and can be charged up slowly using microwave oven transformers. It can then release all its stored energy in under a millisecond through a triggered spark gap. This allows for some pretty big sparks as seen in this video, we are not sure about the laughing in the video maybe the power has gone to his head? Continue reading “24kJ Capacitor Bank”