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Hemp Fibers Make Better Supercapacitors Than Graphene 178

Posted by samzenpus
from the burning-up-and-down dept.
biodata (1981610) writes "BBC News is reporting findings published in the journal ACS Nano by Dr David Mitlin from Clarkson University. Dr. Mitlin's team took waste hemp stems and recycled the material into supercapacitors with performance as good, or better, than those built from graphene, at a fraction of the raw materials cost. "We're making graphene-like materials for a thousandth of the price - and we're doing it with waste. The hemp we use is perfectly legal to grow. It has no THC in it at all - so there's no overlap with any recreational activities," Mitlin says.
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Hemp Fibers Make Better Supercapacitors Than Graphene

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  • by russejl (746370) on Thursday August 14, 2014 @07:03PM (#47674111)
    This is potentially exciting... no pun intended :-)

    The article abstract says:
    The nanosheets are ideally suited for low (down to 0 C) through high (100 C) temperature ionic-liquid-based supercapacitor applications: At 0 C and a current density of 10 A g–1, the electrode maintains a remarkable capacitance of 106 F g–1. At 20, 60, and 100 C and an extreme current density of 100 A g–1, there is excellent capacitance retention (72–92%) with the specific capacitances being 113, 144, and 142 F g–1, respectively. These characteristics favorably place the materials on a Ragone chart providing among the best power–energy characteristics (on an active mass normalized basis) ever reported for an electrochemical capacitor: At a very high power density of 20 kW kg–1 and 20, 60, and 100 C, the energy densities are 19, 34, and 40 Wh kg–1, respectively. "

    Which possibly suggests that the materials are suitable for indoor use (but not in cars unless you happen to operate in a non-freezing climate) which could have some very practical applications. Solar panels are becoming attractive and I'd like a storage bank but would like to avoid batteries because of the slow charge, expense, and maintenance. A super capacitor, of course, is attractive. Off the top of my head, I don't know what the power density of this type of capacitor is relative to lead acid deep cycle batteries. Still, I smile though :)
    • by cbhacking (979169) <been_out_cruising-slashdot&yahoo,com> on Thursday August 14, 2014 @07:38PM (#47674395) Homepage Journal

      The power density is really nowhere close to a battery. Supercaps make sense for things where you actually need really massive charge and/or discharge spikes, over very short times. Think railguns, or a camera flash that can fire multiple times without needing to recharge between shots (if it charged enough to begin with), or possibly a smoothing system for charging batteries from a very spiky power source (hypothetically, this could scale to things like harvesting lightning, though at present that's not at all practical). They aren't practical for long-term storage, either due to energy density or due to their tendency to lose power over time pretty quickly.

      A sufficiently large battery bank will have no problem with the charge speed of a photovoltaic array (which is actually rather slow). A small bank might reach saturation voltage - where the batteries are still charging but can't charge any *faster* or they'll take damage from overvolting - fairly quickly if fed by a large array, but that's not the real problem with a small bank; the real problem is not having enough storage capacity.

      Expense is considerable, especially if you go with the low-maintenance options like gel-cells. However, supercaps are, at this time, not something you can buy a huge bank of at any price (certainly not the hemp-based ones). If you could get a meaningful capacity of the graphene ones it would probably cost many times as much. Maybe the hemp ones will change that, but don't hold your breath.

      Maintenance is much less than it sounds. Wet-cells (typical lead-acid batteries) need topping up with water periodically, and occasionally may need equalization charges; the first can be done by a reminder to go do so every month, and the latter doesn't even need to be that often. Pretty much every other aspect of maintenance should be handled by a good enclosure for the batteries and a good charge controller. The controller costs a bit but you want one of the good ones anyhow; they perform DC-DC voltage conversion to take the output of the solar cells (which can easily be at least 25% higher voltage than the batteries will charge at) and down-convert it, extracting some extra current in the process (some energy is lost in this process, but it's typically a 10%-20% net positive for the 12V gel-cells my family uses). Speaking of gel-cells, those will save you on maintenance (at a cost of more money up front and a more severe voltage sensitivity that limits charge rate a bit harder). Such batteries are basically install-and-forget, but you'd need to be tremendously lazy for them to be worthwhile for a home installation; they are typically for marine usage (as my parents do) where never needing to open the cells (to add water) is a significant plus.

      • by geoskd (321194) on Thursday August 14, 2014 @09:06PM (#47674867)

        The power density is really nowhere close to a battery. Supercaps make sense for things where you actually need really massive charge and/or discharge spikes, over very short times.

        That is the definition of power density. You're thinking energy density. The fact that you would get the two confused casts aspersions on your knowledge in the field.

        It should also be noted that almost all types of batteries have leakage current which renders them unsuitable for long term energy storage. Most super caps have a higher than normal leakage current due to the lower operating resistance of the devices (the same trait which allows them very high power density).

        • The Mazda 6 uses capacitors for it's regenerative braking system...so they are relevant for hybrid car systems...for short term energy storage.

        • by thegarbz (1787294)

          The power density is really nowhere close to a battery. Supercaps make sense for things where you actually need really massive charge and/or discharge spikes, over very short times.

          That is the definition of power density. You're thinking energy density. The fact that you would get the two confused casts aspersions on your knowledge in the field.

          Interesting conclusion. Care to pick apart the rest of his post point by point, or do you naturally simply assume that if someone slips up with one word they are entirely ignorant in their field? I have on occasion confused kW and kWh, that hasn't stopped me from designing HV substations successfully, just like energy density vs power density has nothing to do with the rest of his post about the benefits of wet-cell vs agm.

          • by geoskd (321194)

            Care to pick apart the rest of his post point by point,

            I took serious exception with the entire post, although I had only limited time to respond. In complete: Lead Acid is entirely the wrong technology for home solar installation, in spite of it being the relatively cheapest. The root reason is total energy density. Even though a home system does not have the space or weight limitations that a mobile system requires, lead acid has such a low energy density compared to virtually all modern option that it is not really suitable for any application except car sta

            • by thegarbz (1787294)

              I agree lead acid is not idea but guess what, if you go out right now and say you want a battery storage system for solar to run your house you WILL get a lead acid battery installation and there are many people who have already done so despite your assertion that it's "wrong". You said it yourself, a home system does not have space or weight limitations, so I'm interested why you think it is so wrong? I mean if we can run industrial control systems for 2 days of lead acid batteries why not a house? If othe

        • by cbhacking (979169)

          Apologies, you're correct. You'll note that I used "energy density" later on.

          Also, it may cast doubt on my knowledge (which is actually fair; that's a easy mistake but also a beginner or casual one) but I don't think it casts aspersions; you should look up what that word means. Anyhow, I'm a computer security engineer, not an EE or an electrician. I've only ever wired one large PV-charged, DC-stored home electrical system, and did it with under my father who *is* an EE. I'm guessing that's still one more th

      • by turp182 (1020263)

        Are the gel-cells you refer to also called "sealed lead acid" batteries? If so, then you are correct, they are maintenance free (and good for about 5 years if kept up properly and not overly discharged often).

        • by cbhacking (979169)

          Gel batteries are a form of sealed lead-acid, yes, although not the only such form. Another common one is AGM (Absorbed Glass Mat). I forget exactly why we went with gel instead of AGM cells, but there was some reason (and it wasn't cost; AGM is cheaper). In any case, there's some interesting reading about sealed lead-acid batteries on the mighty Wikipedia: http://en.wikipedia.org/wiki/V... [wikipedia.org]

      • by blackpaw (240313)

        They aren't practical for long-term storage, either due to energy density or due to their tendency to lose power over time pretty quickly.

        I'd be curious to know what you consider long term, as it might not be as long as you think for a home storage situation.

        I have a 1.5kwh array on my home, which generates a little excess during the day and of course, is useless at night :)

        I've considered bumping it up to 3 or 5kwh as I get no effective use out of the excess generation (8c/KwH). However if I could buffer it for 24-48 hours then I could effectively power my house overnight. I live in Brisbane, Australia, so it would be effectively off grid fo

    • by mlts (1038732) on Thursday August 14, 2014 @09:39PM (#47674975)

      I'd love these for a solar array where energy stored for unit volume is important, but not critical (like it is in a car or RV) for a number of reasons:

      1: Hemp is a lot less nasty for the environment than graphene.

      2: This could be used as a buffer for the chemical batteries, since you don't have to worry about limiting amps coming in. Come "shoulder hours", the supercaps can be charging the batteries at exactly the amperage rate they need even after the sun is down, greatly improving the system's efficiency.

      3: The lifespan of a capacitor is a lot longer than a battery because electricity is stored physically, not chemically. So, if space is less of an issue, large supercaps can be used without worrying about replacement every 5-10 years (or 2-3 years with Li-ion) batteries.

      So, for an off-grid circuit (one that never goes near mains power and pretty much acts as a UPS), having this technology would go far.

    • There's another approach to this, but it's gone a bit quiet ; they use a novel dielecric and claim that they can get incredibly high voltages out of it which makes for high energy storage.

      EEStor [wikipedia.org]

      Since the dielectric is one part and the electrode another, I wonder what kind of advantages you'd get from combining the two? (Not sure if hemp electrodes would be compatible with their manufacturing process which uses metal foils as electrodes at the moment, as per traditional capaciptors).

  • by ilsaloving (1534307) on Thursday August 14, 2014 @07:06PM (#47674131)

    This will give new meaning to the term 'magic smoke'.

    ( http://en.wikipedia.org/wiki/M... [wikipedia.org] for those that don't know)

    • Have you ever made hemp fiber supercapacitors...on weed?
  • Legal... sort of (Score:4, Informative)

    by michael_cain (66650) on Thursday August 14, 2014 @07:11PM (#47674179) Journal
    "The hemp we use is perfectly legal to grow."

    Yeah, if you're properly affiliated with a university or state department of agriculture, are doing it for research purposes, and have agreed to all of the terms and conditions that the feds and your local state require. If you or I try to do it commercially, it's a federal felony.
    • by GrahamCox (741991) on Thursday August 14, 2014 @07:16PM (#47674217) Homepage
      Which is nuts, actually. Hemp is a brilliant raw material with hundreds of practical uses which *should*, if people had any sense of balance, far outweigh the small issue of the cannabinoids. It could probably even be selectively bred to eliminate that aspect, but no, concern about a few potheads sends legislators into a tailspin. This is why we can't have nice things.
      • by rahvin112 (446269)

        Yea but it looks like pot and if you allow any Joe, Dick and Jane to grow it the feds would have to genetically test every plant in the crop and that's just unworkable so it should be banned to save the government effort in proving that you are growing illegal plants.

        [/sarcasm]

      • Re:Legal... sort of (Score:5, Informative)

        by TapeCutter (624760) on Thursday August 14, 2014 @07:56PM (#47674535) Journal

        It could probably even be selectively bred to eliminate that aspect

        That's been available for a very long time, it's what they used in this experiment and is grown commercially to make hemp clothing. Getting permission to grow those species is unreasonably difficult in many countries for no other reason than it looks like the smokeable stuff. Historically hemp is as important as cotton, George Washington once decreed every land holder set aside a portion of land for growing hemp to supply the colonial navy with rope. It's said that the invention of nylon spurred the original US government propaganda and the prohibition drive, hemp was a direct competitor in many markets and the nylon makers had powerful friends in congress. The propaganda avoided the word "hemp" and used the Mexican name "Marijuana" in a cynical attempt to appeal to the racist dogma of the day that branded Mexicans as lazy and untrustworthy.

      • Cotton lobby (Score:4, Insightful)

        by rsilvergun (571051) on Thursday August 14, 2014 @08:45PM (#47674795)
        there's more to it than just Mary Jane. You don't think the cotton lobby has noticed the wonder material that is hemp?...
      • by drinkypoo (153816)

        It could probably even be selectively bred to eliminate that aspect, but no, concern about a few potheads sends legislators into a tailspin. This is why we can't have nice things.

        Well congrats, you've just completely mischaracterized the situation. Concern about diminishing of a profit center (Big Pharma) sends legislators into a tailspin. This is why we can't have nice things. Also, they can't admit they've been lying to us through their corrupt fucking faces all this time. The legislators know that weed is harmless, that's what the science has always said.

    • Re:Legal... sort of (Score:4, Informative)

      by dbIII (701233) on Thursday August 14, 2014 @09:56PM (#47675017)
      It's one of the reasons France gave the USA the finger and you guys decided to hate the nation that used to be admired - France still has a large and legal hemp industry for fibre production. They refused to shut it down as part of the "war on drugs". India grows a vast amount of the stuff for fibre. There's a few other places that didn't decide to wipe out an industry as collatoral damage in the "war on drugs" distraction.
    • Of course you have to comply with state and federal regulations. They probably include random sampling by feds to test THC levels in your crop.
      If you genetically modify corn to have THC the corn farmers will face the same thing. That's not wrong.

      What is wrong is that THC is illegal in the US. But that is a different discussion.
      Info: I live in the Netherlands. I know a society can work properly while weed is available to everyone (although it isn't perfect yet).

  • by kruach aum (1934852) on Thursday August 14, 2014 @07:13PM (#47674189)

    What about basket weavers, you insensitive clod!

  • by msobkow (48369) on Thursday August 14, 2014 @07:13PM (#47674193) Homepage Journal

    Sorry, but every cannabis sativa plant, whether of the recreational, medicinal, or hemp varieties produces some THC. Granted, hemp is a miniscule fraction of a percentage THC, but it does have THC.

    • by dbIII (701233)
      Friend of a friend story but probably true.
      A friend of mine, his sister and his sister's stoner boyfriend went to Latvia after the Russians moved out and they could reconnect with family etc. The stoner was astonished with hemp growing all over the place and he collected and dried a lot of it. It turns out that with the variety there and the short growing season he was effectively just smoking rope because whatever process forms THC just didn't get time to happen.
      • The concept of dirtweed or ditchweed is well-known to US stoners as well - if you find it growing naturally there is a good chance it's a hemp strain, not suitable for smoking. It's not that the these plants don't contain any THC, it's that they don't contain appreciable THC in doses large enough to get high. It's a minor distinction, and probably good not to mention it lest the government try to clamp down on supercapacitor research. But, I would expect the scientist in the article to be more precise.
    • by BitZtream (692029)

      ... They're talking about hemp, not Cannabis Sativa. Theres a difference.

      http://en.wikipedia.org/wiki/H... [wikipedia.org]

      There are many strains of Cannabis, some have THC, some don't.

  • by bobbied (2522392) on Thursday August 14, 2014 @07:14PM (#47674201)

    Dang it folks, I left the farm to be an electrical engineer and it keeps following me! I ran away from the farm for a reason, and bailing twine was wrapped all around it.

    Now we are going to be making capacitors from bailing twine? NOOOOOO!! I won't do this again!

    I have to retire before they start sending me out to pickup packages of dried grass and haul them to the barn again.

  • Marijuana... (Score:5, Interesting)

    by geekd (14774) on Thursday August 14, 2014 @07:25PM (#47674281) Homepage

    Marijuana. Is there anything it CAN'T do?

  • But, can it be converted into a bong?

  • by UnknownSoldier (67820) on Thursday August 14, 2014 @07:33PM (#47674357)

    https://www.youtube.com/watch?... [youtube.com]

    The hypocrisy of the government is retarded.

    --
    "It is the government proselytizing it is propaganda. When it is people promoting it, it is outlawed."

    • by roc97007 (608802)

      I don't have a reference handy, (would have to ask a certain member of my family who would know all about this) but I seem to remember that the banning of hemp had nothing to do with THC. That was only an excuse. The real reason was that hemp was competing too well with some other part of the textile industry.

      That's going to bug me. I'll have to do research tonight and get more details.

  • ... capacity for any recreational activities.

    • by riverat1 (1048260)

      Actually when I was in high school electronics class we had great fun charging up big capacitors then tossing them to our classmates yelling "Here, catch!". A few of us were smart enough not to catch.

      • by roc97007 (608802)

        Actually when I was in high school electronics class we had great fun charging up big capacitors then tossing them to our classmates yelling "Here, catch!". A few of us were smart enough not to catch.

        In my high school electronics class the instructor announced on the first day of class that anyone charging up a capacitor and tossing it to someone else as a joke would automatically fail the class. (Apparently this was not his first rodeo.)

        Up to that point, we'd never even realized this was possible. That Halloween was fun.

        • by riverat1 (1048260)

          Yea, it only took our instructor a couple of days to tell us to stop too but by that time everyone was wise to it anyway.

      • My high school instructor told us that when he was in high school electronics, the kids would toss a charged capacator at you if they saw you trying to sneak in after the bell rang. Either you try your best to catch it, or you let it drop and the professor turns around from the chalk board and notices you walking in.

        • My high school instructor told us that when he was in high school electronics, the kids would toss a charged capacator at you if they saw you trying to sneak in after the bell rang. Either you try your best to catch it, or you let it drop and the professor turns around from the chalk board and notices you walking in.

          But he didn't hear the snap of the discharge if the late student caught it?

  • by PPH (736903) on Thursday August 14, 2014 @08:01PM (#47674575)

    Administrator: What are you guys doing in the lab with all those plants?

    Undergrad lab assistant: Testing them for use as supercapacitor electrodes. Yeah. That's the ticket.

    Administrator walks away satisfied.

  • by roc97007 (608802) on Thursday August 14, 2014 @08:03PM (#47674587) Journal

    Experimenter bias?

  • by angel'o'sphere (80593) on Thursday August 14, 2014 @08:16PM (#47674635) Homepage Journal

    The hemp we use is perfectly legal to grow. It has no THC in it at all - so there's no overlap with any recreational activities," Mitlin says.
    A shame, isn't it?

    • The good part is, instead of throwing the stems out I can now recycle them!
      • He he, but ropes etc. are made from hemp stems since ages, you missed out on that.
        Nut frankly making high tech from them is much more exiting!

  • oh no, soon our computers will be confused and forgetful ..

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