Connect with us

Hi, what are you looking for?


Energy Storage

New Graphene + Carbon Nanotube Supercapacitor Rivals Lithium Battery

An international team of researchers has come up with a recipe for a microscale flexible energy storage device made of graphene and carbon nanotubes, which can store enough energy to rival the gold standard, lithium batteries. That’s significant because the device is actually not a battery, it is a supercapacitor that can charge and discharge much faster than a battery.

It’s also significant because the research team has devised a fabrication method that results in a long fiber (long as in 50 meters long, so far). That opens up all sorts of opportunities for weaving the new supercapacitor into clothing to power portable electronics. Since the fiber also doubles as a conductor, it can also be used in place of wires to reduce the size and weight of portable devices, including medical implant.

graphene CNT supercapacitor

Previous study of graphene/CNT supercapacitor (published 2009) courtesy of Case Western.

Batteries vs. Supercapacitors: A Quick Review

Batteries and supercapacitors both store energy, but there’s a catch. Batteries have a higher energy density which means they can store energy for longer periods, but they have low power density. That means they can’t discharge quickly.

Supercapacitors have the opposite problem: their low energy density means they can’t store as much energy, but their high power density enables them to deliver energy rapidly when needed.

The trick to solving the energy density problem for supercapacitors is to find a material with a relatively high proportion of surface area available for energy storage.

That’s where graphene, the “nanomaterial of the new millennium” comes in. A new material discovered just 10 years ago, graphene consists of a sheet of carbon just one atom thick. The two-dimensional structure is basically all surface area, but the notoriously finicky graphene presents a whole raft of challenges for translating its powers into energy storage, photovoltaics, and other fields.

Taming Graphene For A Graphene/Carbon Nanotube Supercapacitor

The schematic above is from a 2009 work on graphene/carbon nanotube hybrid supercapacitors by Dingshang Yu of Nanyang Technological University in Singapore and Case Western’s and Laming Dai, who are also members of the current international research team (China is also participating, through Tsinghua University).

That work tackled a huge problem with graphene. Other efforts had shown that though the hybrid approach was promising, the graphene was not cooperating:

…most of the above-mentioned techniques [for obtaining graphene film] suffer from a lack of the film architecture/property control, leading to the loss of the surface area for energy storage due to graphene aggregation. For energy storage applications, therefore, it is highly desirable to use one-dimensional (1D) carbon nanotubes (CNTs) to physically separate 2D GNs to preserve graphene’s high surface area.

The 2009 study arrived at a self-assembly process to solve the problem, resulting in a graphene/carbon nanotube film.

A Hybrid Supercapacitor Fiber

The current study, led by Yuan Chen of Nayang Technological University and co-authored by Dai, has just been published in Nature Nanotechnology. It details how the team translated the self-assembly technique into a long fiber:

A solution containing acid-oxidized single-wall nanotubes, graphene oxide and ethylenediamine, which promotes synthesis and dopes graphene with nitrogen, is pumped through a flexible narrow reinforced tube called a capillary column and heated in an oven for six hours.

The advantage of this structure is the enormous amount of available surface area for both energy storage and charge conduction, clocking in at a whopping 396 square meters per gram of fiber.

The favorable comparison to lithium was demonstrated in a solid state micro-supercapacitor, which the research team assembled from two graphene/carbon nanotube fibers. With a polyvinyl alcohol/phosphoric acid gel as an electrolyte, the device achieved a density of 6.3 microwatt hours per cubic millimeter.

According to the research team, that compares to a 4 volt/500 microampere-hour thin film lithium battery.

They also found something interesting about how the fibers are arranged. When three pairs of fibers were arranged in a series, the voltage tripled and the time for charge/discharge stayed the same.

However, when three pairs are arranged in parallel, both the output current and the charge/discharge time tripled.

There could also be some significant advantages when it comes to cost and supply chain issues. Compared to lithium, carbon nanotubes and graphene are cheaper and more readily available.

Also lending an assist with favorable cost comparisons, the hybrid supercapacitor appears to have a much longer lifecycle than conventional rechargeable batteries.

The team tested their supercapacitor at 10,000 charge/discharge cycles and came up with a performance retention of about 93 percent. Conventional rechargeables generally lose performance before they hit the 1,000-cycle mark.

To cap it off, the fibers also retained performance when subjected to flexibility and stress tests.

Stay tuned, because the research team is also thinking ahead to applying their new supercapacitors to batteries, solar cells, and microbial fuel cells.

Follow me on Twitter and Google+.

Keep up with all the latest clean tech news from CleanTechnica: subscribe to our newsletter.


Sign up for daily news updates from CleanTechnica on email. Or follow us on Google News!

Have a tip for CleanTechnica, want to advertise, or want to suggest a guest for our CleanTech Talk podcast? Contact us here.

Former Tesla Battery Expert Leading Lyten Into New Lithium-Sulfur Battery Era — Podcast:

I don't like paywalls. You don't like paywalls. Who likes paywalls? Here at CleanTechnica, we implemented a limited paywall for a while, but it always felt wrong — and it was always tough to decide what we should put behind there. In theory, your most exclusive and best content goes behind a paywall. But then fewer people read it! We just don't like paywalls, and so we've decided to ditch ours. Unfortunately, the media business is still a tough, cut-throat business with tiny margins. It's a never-ending Olympic challenge to stay above water or even perhaps — gasp — grow. So ...
If you like what we do and want to support us, please chip in a bit monthly via PayPal or Patreon to help our team do what we do! Thank you!
Written By

Tina specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Views expressed are her own. Follow her on Twitter @TinaMCasey and Spoutible.


You May Also Like

Clean Transport

Once again, European cities are outperforming American ones on the electrification of bus transit. I’ve talked about this before, but nothing has changed and...


Electric vehicle makers in the US may struggle to qualify their customers for a federal tax credit under new rules set by the Inflation...


Tiny Luxembourg aims to dominate the graphene nanotube market for next-generation EV batteries and other sustainable tech.

Clean Power

Brothers in Rice lab find audio from graphene production contains valuable data Originally published on Rice University, Rice News. By Mike Williams It may...

Copyright © 2023 CleanTechnica. The content produced by this site is for entertainment purposes only. Opinions and comments published on this site may not be sanctioned by and do not necessarily represent the views of CleanTechnica, its owners, sponsors, affiliates, or subsidiaries.