Graphene Super Caps: Coming Soon?

If you read Hackaday regularly, you’ve probably heard that you can use a LASER to create graphene. There’s been a bit of research on how to make practical graphene supercapacitors using the technique (known as LIG or LASER-induced graphene). Researchers at Rice University have been working on this, and apparently they’ve had significant success inducing graphene capacitors on a Kapton substrate. The team has published a paper in Advanced Materials (which is behind a paywall) about their work.

In particular, Rice claims that they have easily produced supercapacitors with an energy density of 3.2 mW/cubic centimeter (that’s what the University’s website reports; they probably mean mW-hours/cubic centimeter) with capacitances near one millifarad per square centimeter. A key benefit of the construction method is that the capacitors continued to work after researchers bent them 10,000 times. A flexible capacitor is useful in wearable devices that would often flex, or in a device like a cell phone that could bend in your back pocket as you sit.

Continue reading “Graphene Super Caps: Coming Soon?”

Paper Thin Conductors

Swedish scientists have created something they call power paper by using nanocellulose and a conductive polymer. The paper is highly conductive and has applications in supercapacitor technology and printed electronics.

The paper, technically called NFC-PEDOT paper, combines high conductivity and compatibility with conventional paper handling machines that could lead to less expensive manufacturing. The team used the material to create supercapacitors (up to 2F) as well as FET-like transistors known as OECTs (Organic Electrochemical Transistors).

Admittedly, the supercapacitor prototype didn’t look very practical (as they dunked it in a beaker full of potassium chloride). The black-colored paper is relatively conductive (42,000 S/m at 20 degrees C), at least for a paper. As a point of reference, silicon is about 1,000 S/m and iron conducts at about 10,000,000 S/m.

What can we do with NFC-PEDOT? Time will tell. We couldn’t help but wonder, however, if paper-based 3D printing couldn’t be adapted to use paper as an insulator or dielectric, foil as a conductor, and something like this material to build resistive elements. After all, we’ve seen something similar using foil and paper before.

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.

Continue reading “Better Capacitors Through Nanotechnology”

Mostly Non-Volatile Memory With Supercapacitors

Back in the days of old, computers used EPROMs to store their most vital data – usually character maps and a BASIC interpreter. The nature of these EPROMs meant you could write to them easily enough, but erasing them meant putting them under an ultraviolet light. Times have changed and now we have EEPROMs, which can be erased electronically, and Flash, the latest and greatest technology that would by any other name be called an EEPROM. [Nicholas] wanted an alternative to these 27xx-series EPROMs, and found his answer in supercapacitors.

[Nick]’s creation is a mostly non-volatile memory built around an old 62256 32k SRAM. SRAM is completely unlike EPROMs or Flash, in that it requires power to keep all its bits in memory. Capacitor technology has improved dramatically since the 1980s, and by using a supercap and one of these RAM chips, [Nick] has created a substitute for a 27-series EPROM that keeps all its memory alive for days at a time.

The circuit requires a small bit of electronics tucked between the EPROM socket and the SRAM chip; just enough to turn the 12 Volts coming from the EPROM programming pin to the 5 Volts expected from the SRAM’s Write Enable pin. This is accomplished by a few LEDs in series, and a 0.1F 5.5V supercap which keeps the SRAM alive when the power is off.

As for why anyone would want to do this when modern technologies like Flash can be found, we can think of two reasons. For strange EPROM sizes, old SRAMs abound, but a suitable Flash chip in the right package (and the right voltage) might be very hard to find. Also, EEPROMs have a write lifetime; SRAMs can be written to an infinite number of times. It’s not the best solution in every case, but it is certainly interesting, and could be useful for more than a few vintage computing enthusiasts.

This project makes us think of another where an LED may have been supplying keep-alive power to some volatile memory.

Hackaday Prize Semifinalist: Artificial Muscles and Supercapacitors

For [Lloyd T Cannon III]’s entry to the Hackaday Prize, he’s doing nothing less than changing the way everything moves. For the last 100 years, internal combustion engines have powered planes, trains, and automobiles, and only recently have people started looking at batteries and electric motors. With his supercapacitors and artificial muscles, [Lloyd] is a few decades ahead of everyone else.

There are two parts to [Lloyd]’s project, the first being the energy storage device. He’s building a Lithium Sulfur Silicon hybrid battery. Li-S-Si batteries have the promise to deliver up to 2000 Watt hours per kilogram of battery. For comparison, even advanced Lithium batteries top out around 2-300 Wh/kg. That’s nearly an order of magnitude difference, and while it’s a far way off from fossil fuels, it would vastly increase the range of electric vehicles and make many more technologies possible.

The other part of [Lloyd]’s project is artificial muscles. Engines aren’t terribly efficient, and electric motors are only good if you want to spin things. For robotics, muscles are needed, and [Lloyd] is building them out of fishing line. These muscles contract because of the resistive heating of a carbon fiber filament embedded in the muscle. It’s been done before, but this is the first project we’ve seen that replicates the technique in a garage lab.

Both parts of [Lloyd]’s project are worthy of a Hackaday Prize entry alone, but putting them together as one project more than meets the goal: to build something that matters.

The 2015 Hackaday Prize is sponsored by:

Home Brew Supercapacitor Whipped Up In The Kitchen

[Taavi] has a problem – a wonky alarm clock is causing him to repeatedly miss his chemistry class. His solution? Outfit his clock radio with a supercapacitor, of course! But not just any supercapacitor – a home-brew 400 Farad supercap in a Tic Tac container (YouTube video in Estonian with English subtitles.)

[Taavi] turns out to be quite a resourceful lad with his build. A bit of hardware cloth and some stainless steel from a scouring pad form a support for the porous carbon electrode, made by mixing crushed activated charcoal with epoxy and squeezing them in a field-expedient press. We’ll bet his roommates weren’t too keen with the way he harvested materials for the press from the kitchen table, nor were they likely thrilled with what he did to the coffee grinder, but science isn’t about the “why?”; it’s about the “why not?” Electrodes are sandwiched with a dielectric made from polypropylene shade cloth, squeezed into a Tic Tac container, and filled with drain cleaner for the electrolyte. A quick bit of charging circuitry, and [Taavi] doesn’t have to sweat that tardy slip anymore.

The video is part of a series of 111 chemistry lessons developed by the chemistry faculty of the University of Tartu in Estonia. The list of experiments is impressive, and a lot of the teaser stills show impressively exothermic reactions, like the reduction of lead oxide with aluminum to get metallic lead or what happens when rubidium and water get together. Some of this is serious “do not try this at home” stuff, but there’s no denying the appeal of watching stuff blow up.

As for [Taavi]’s supercap, we’ve seen a few applications for them before, like this hybrid scooter. [Taavi] may also want to earn points for Tic Tac hacks by pairing his supercapacitor with this Tic Tac clock.

[Thanks, Lloyd!]

Meshing Pis with Project Byzantium

If internet service providers go down, how are we going to get our devices to communicate? Project Byzantium aims to create an “ad-hoc wireless mesh networking for the zombie apocalypse.” It’s a live Linux distribution that makes it easy to join a secure mesh network.

[B1tsh1fter] has put together a set of hardware for running Byzantium on Pis in emergency situations. A Raspberry Pi 2 acts as a mesh node, using a powerful USB WiFi adapter for networking. Options are provided for backup power, including a solar charger and a supercapacitor based solution.

The Pi runs a standard Raspbian install, but uses packages from the ByzPi repository. This provides a single script that gets a Byzantium node up and running on the Pi. In the background, OLSR is used to route packets through the mesh network, so that nodes can communicate without relying on a single link.

The project has a ways to go, but the Raspberry Pi based setup makes it cheap and easy to get a wide area network up and running without relying on a single authority.