By on February 25, 2013

Micro-supercapacitor-prv UCLA Photo

Energy density isn’t the only reason why battery-powered cars have never caught on. As was highlighted in Tesla’s somewhat less than successful media road trip, the amount of time it takes to fill batteries with electrons can be as significant a factor in the practicality of EVs as the amount of electrons those batteries can hold.

That’s one of the reasons why high power capacitors, also known as supercapacitors or ultracapacitors, have held promise – caps can charge and discharge very quickly. That promise, though, has been held back by the old bugaboo of energy density. Capacitors unfortunately have limited capacity. Researchers at UCLA who had previously announced the almost accidental discovery of a simple and inexpensive method of creating graphene sheets, which have ideal properties for fabricating ultracapacitors, have now published the results of their further research, demonstrating a scalable process for fabricating flexible graphene micro-supercapacitors that have some of the highest energy densities achieved yet for such capacitors.

 

The team, led by Richard Kaner, is developing the devices out of one of those fortuitous discoveries that expands the frontiers of science, like penicillin or nylon. Maher El-Kady, of Kaner’s lab, had invented an elegantly simple and inexpensive method of making graphene, a single atom thick sheet of carbon atoms arranged in that hexagonal latice that C loves so well. He poured out a layer of graphite oxide solution on a plastic substrate and then exposed it to laser light. The process wasn’t the most clever thing about El-Kaner’s discovery, it was the equipment that he used. El-Kaner’s substrates were DVDs and he used a standard consumer grade LightScribe DVD burner for the laser. Refining the process, the team has now figured out a way to embed electrodes into the graphene, which is formulated over a flexible film, and they claim energy density comparable to current thin-film lithium ion batteries.

Often “scalable” means scaling up, but Kaner and El-Kady discovered that scaling down has advantanges. Miniaturizing the devices enhances charge storage capacity and charge/discharge rate and it also allowed them to produce more than 100 micro-supercapacitors on a single disc in 30 min or less. The flexible substrate allows for packaging options and the size means that they can be mounted on the back of solar cells or other chips.

As is always the case with potential energy gamechangers, the research team is looking for partners to produce their invention in industrial quantities. While the initial applications will likely not be for transportation, any development concerning electrical storage that combines enhanced energy density, faster charge/discharge rates, and lightweight miniaturization is bound to attract attention from the EV crowd.

UCLA press release here.

Ronnie Schreiber edits Cars In Depth, a realistic perspective on cars & car culture and the original 3D car site. If you found this post worthwhile, you can dig deeper at Cars In Depth. If the 3D thing freaks you out, don’t worry, all the photo and video players in use at the site have mono options. Thanks for reading – RJS

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23 Comments on “Are Graphene Micro-Supercapacitors An EV Gamechanger?...”


  • avatar
    Dr. Kenneth Noisewater

    Having these both for vehicle storage and “pump priming” (whereby the “filling station” is connected to a typically-sized electric service, which fills an array of these capacitors up slowly, then when a vehicle connects they discharge rapidly) would be a game changer IMO.

    I didn’t see details on the energy density achieved though.. It would probably need to be on the order of 1500-2000 Farads/gram to match what’s expected of next-gen batteries..

    • 0 avatar
      redav

      “Having these both for vehicle storage and “pump priming” (whereby the “filling station” is connected to a typically-sized electric service, which fills an array of these capacitors up slowly, then when a vehicle connects they discharge rapidly) would be a game changer IMO.”

      I’ve had that thought, too. There’s no reason for charging to be limited by instantaneous power available to the electric dispenser. Capacitance is a fundamental tool of system design (not just electrical, but fluid, mechanical, and even manufacturing plant layout), that it would seem unfathomable not to use it.

    • 0 avatar
      mcs

      A side benefit could be a ready supply of power for your house in case of a power failure. Not a bad idea. Could be used to grab power for the house at off-peak hours as well.

    • 0 avatar

      From the abstract to their recent paper: “These micro-supercapacitors demonstrate a power density of ~200 W cm−3″.

  • avatar
    modelt1918

    I learned about graphene a couple of months ago. This technology is going to be future for many things.Most people don’t have any idea what it is and yet, it is the new hot tech of the future.

  • avatar
    raincoaster

    I’d like to nominate the phrase “game changer” to be taken out back and shot.

  • avatar
    areader

    Cabot chemical just announced a graphene additive, “LITX G700″ for makers of lithium ion batteries which they claim will provide better energy density. Lots of work going on with huge potential.

  • avatar
    macnab

    The UCLA press release says nothing about capacitance, internal resistance or breakdown voltage. It’s a silly announcement.

    • 0 avatar

      In the post there’s a link to the team’s most recent published research. I can’t access the complete paper without paying a fee, but I’m guessing that the paper itself discusses the capacitance, internal resistance and breakdown voltage. I don’t expect press releases to get very technical. I’m sure that if you contact Kaner or El-Kady at UCLA they’ll give you that data.

    • 0 avatar
      dbyam

      “…and they claim energy density comparable to current thin-film lithium ion batteries.”

      I couldn’t find that claim about energy density in the press release. Did I miss it? That would be a bold EEstor level assertion.

  • avatar
    redmondjp

    There is one problem with using a capacitor for energy storage when compared to a battery: their voltage changes greatly vs. state of charge. This means that more sophisticated electronics are required in order to utilize the energy (increasing the cost, amount of required electronics, likelihood of failure, and decreasing energy efficiency). Basically you have to use switching power supply technology to boost or buck the voltage on a continual basis.

    For example, a 6-cell lead-acid battery voltage ranges from 12.76V (fully charged, no load) to around 9V (low-voltage cutoff, under load). A 12V capacitor ranges from 12V fully-charged to ZERO volts. Big difference.

    I know that the hybrid buses used locally do use ultracapacitors (one of these rooftop-mounted hybrid units had a visually spectacular fire on the freeway a few weeks ago that made the news).

    • 0 avatar
      rodface

      This one?

      http://www.king5.com/news/cities/seattle/Bus-fire-shuts-down-I-5-express-lanes-186472611.html

      • 0 avatar
        redmondjp

        Yup – that’s the one! They say in that article that the cause of the fire was a locked-up rear brake, but this is a hybrid bus so part of the (regenerative) braking system is the ultracapacitor storage bank on the roof, which was also on fire.

    • 0 avatar
      Luke42

      That’s not too different from what’s required to make an EV with a lithium ion battery and regenerative braking work.

      The lithium ion battery requires a BMS, and regenerative braking adds the voltage buck problem. Add in a requirement to not smoke the tires with a traction-aware PWM controller, and you’re right there in terms of complexity with existing EV designs.

      And these complex power electronics work pretty well. At least in the Prius in my driveway (even more complex), and in the LEAF that I drove (which has fantastic NVH).

  • avatar
    Maxseven

    Hmmm, this announcement has the flavor of the mystical (and mythical?) EEStor technology. I wonder if the government has sent its ‘dark programs’ facilitators in for a closer look yet. :)

  • avatar
    schmitt trigger

    redmondjp:
    are you positive (no pun intended!) about that particular bus employing ultracapacitors and not batteries as its primary energy-storing media?
    As mentioned in the article, ultracapacitors have a very low energy vs volume ratio, and would provide even shorter range than a battery. They are used to “top off” batteries, but are not really used as its main storage.

    The only pure ultracapacitor bus I’ve seen is in Shanghai. But to avoid the short range issue, at each of the scheduled stops they raise a pantograph that touches a pair of contacts high above the stop. Then while the passengers embark/disembark, the capacitor’s charge is topped off and it lasts enough for the one kilometer or so until the next stop.

  • avatar
    nikita

    The speed at which batteries can be recharged is not going to be significantly increased without a decrease in battery life. That is the use for these capacitors that is the point of this article. Maybe a future breakthrough in battery chemistry or construction will make pure EV’s mainstream, but I dont see this idea doing it, but maybe it could complement those future batteries.


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