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Capacitors to Replace Batteries? 499

Posted by CowboyNeal
from the going-and-going-and-going dept.
An anonymous reader writes "MIT's Joel Schindall plans to use old technology in a new way with nanotubes. 'We made the connection that perhaps we could take an old product, a capacitor, and use a new technology, nanotechnology, to make that old product in a new way.' Capacitors contain energy as an electric field of charged particles created by two metal electrodes, and capacitors charge faster and last longer than normal batteries, but the problem is that storage capacity is proportional to the surface area of the battery's electrodes. MIT researchers solved this by covering the electrodes with millions of nanotubes. 'It's better for the environment, because it allows the user to not worry about replacing his battery,' he says. 'It can be discharged and charged hundreds of thousands of times, essentially lasting longer than the life of the equipment with which it is associated.'"
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Capacitors to Replace Batteries?

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  • Oh great (Score:5, Funny)

    by tygerstripes (832644) on Friday June 09, 2006 @07:45AM (#15501072)
    I'm sick of that bloody rabbit. Now it's going to last forever. Perfect.
  • Woohoo! (Score:2, Funny)

    by Anonymous Coward
    Finally... the flux capacitor we've all been looking for!
  • by Chrisq (894406) on Friday June 09, 2006 @07:46AM (#15501078)
    I thought the charge was on the parts of the plates nearest each other, so the surface area would only be that of the ends of the nano-tubes. This would be smaller than if they had a flat plate!
    • by tygerstripes (832644) on Friday June 09, 2006 @07:49AM (#15501090)
      Good point. Maybe the nanotubes actually mesh between each other - kind of like the teeth in gears. Can't see it being easy to manufacture, but that would definitely provide a massive increase in closest-point surface area.
    • by mprinkey (1434) on Friday June 09, 2006 @07:58AM (#15501127)
      I believe that the height of the carpet of the nanotubes on the electrodes is going to be small relative to the thickness of the dielectric material between the electrodes. That dielectric thickness is the limiting factor for typical capacitors. The dielectric can only be so thin before it can no longer prevent current flow, maintain mechanical integrity, etc. Otherwise, you could store unlimited energy in a capacitor by making the dielectric thinner and thinner. With these, the dielectric thickness can stay the same, but the surface area on each electrode can be much higher. That is like making a physically bigger capacitor.
    • by Stellian (673475) on Friday June 09, 2006 @08:11AM (#15501180)
      The nanotubes are there to tremendously increase the surface of one electrode. All electrolytic capacitors I know use some sort of oxide as dielectric, and I presume the oxide would cover the whole nanotube. The other electrode is constituted by the solid/liquid electrolyte that the nanotubes are immersed in, surrounding them from all directions and utilizing the exceptional surface increase.
      So the nanotubes from one electrode are not immersed in dielectric (insulator), they are immersed in the other electrode.
    • by TeknoHog (164938) on Friday June 09, 2006 @08:14AM (#15501194) Homepage Journal

      In electrolytic capacitors, one electrode is formed by a conducting liquid, and an oxide layer on the metallic conductor acts as the insulator. The nanotube version may use something like this.

      On another note, every time someone proposes to replace batteries with capacitors, I wonder how they make up for the huge variation of voltage that a capacitor delivers. Basically, the voltage of a capacitor is proportional to the amount of charge stored, whereas a battery provides more or less constant voltage. The capacitor-battery would require a circuit (something like a switching power supply) to be able to provide constant voltage. That, in turn, would take up space and waste some energy.

      • On another note, every time someone proposes to replace batteries with capacitors, I wonder how they make up for the huge variation of voltage that a capacitor delivers. Basically, the voltage of a capacitor is proportional to the amount of charge stored, whereas a battery provides more or less constant voltage.

        That's an excelent point.
        One solution to avoid a switching supply, would be to create a simple circuit that ties capacitors series/parallel as they discharge, to keep a more or less constant voltage.

      • I've read that they've already got a good solution for this, and you're right, it is just a voltage regulator of some sort. The only thing keeping them from using capacitors right now is their small capacity. My memory of this sort of thing is a little fuzzy, but here's how I figure it:

        Q = CV (where Q = charge, C = capacitance and V = voltage).

        There's absolutely no problem regulating the voltage as it comes off of the capacitor, the biggest problem is getting the maximum Q high enough to supply more than a
      • by Rob the Bold (788862) on Friday June 09, 2006 @09:23AM (#15501558)
        I wonder how they make up for the huge variation of voltage that a capacitor delivers. Basically, the voltage of a capacitor is proportional to the amount of charge stored, whereas a battery provides more or less constant voltage. The capacitor-battery would require a circuit (something like a switching power supply) to be able to provide constant voltage. That would . . . waste some energy.

        There are some very efficient (90%+) DC/DC converters available right now. Some will even automatically switch from step-up to step-down mode on-the-fly. Many battery powered devices already use these ICs to supply the multiple voltages needed, e.g. 1.5V and 3.3V logic, and 10-14V for a white LED backlight in phones and digital cameras So designing these devices to use a nanotube capacitor wouldn't necessarily require a more complex or less efficient power supply. So I think we can solve the voltage issue if they can build the capacitors.

    • by d3ac0n (715594) on Friday June 09, 2006 @08:27AM (#15501250)
      Did you guys actually read FTA? There is a SEM Photo of one of the nanotube sections. The tubes are aligned VERTICALLY on the Cap surface, much like a carpet. Since the tubes themselves hold the charge, each individual nanotube fiber holds electricity. That's ALOT of power!
  • Riverworld anyone? (Score:5, Interesting)

    by LaminatorX (410794) <> on Friday June 09, 2006 @07:47AM (#15501083) Homepage
    Philip Jose Farmer predicted "batacitors" in his novels decades ago. Chalk annother one up for life imitating science fiction.
    • by Whiney Mac Fanboy (963289) * <> on Friday June 09, 2006 @07:55AM (#15501110) Homepage Journal
      Philip Jose Farmer predicted "batacitors" in his novels decades ago. Chalk annother one up for life imitating science fiction.

      Well - its a bit of a no-brainer to any EE kind of guy. No wasteful energy conversion process, etc etc.

      Everyone's been waiting for the materials technology to catch up to the rather obvious idea that's all :-)
    • Actually, the idea of capacitors as electrical storage devices goes back a couple centuries before that:

      If I remember correctly, Benjamin Franklin wasn't trying to prove that there was electricity in clouds when he performed his legendary experiment of a key on a kite. He was trying to see if he could charge a Leyden Jar [] with a lightning stroke.

      The problem was, back then they didn't have any use for electricity (no computers or Hello Kitty Vibrators) so this was more of an entertainment/scientific-cur

      • by Chelloveck (14643) on Friday June 09, 2006 @09:14AM (#15501492) Homepage
        [...] back then they didn't have any use for electricity (no computers or Hello Kitty Vibrators) [...]

        It was a sad, sad time to be Hello Kitty.

  • Fascinating (Score:4, Interesting)

    by Claws Of Doom (721684) on Friday June 09, 2006 @07:54AM (#15501109)
    The fast charge has its obvious benefits, but I'm wondering about the durability of such nanotube filaments in the face of, say, the treatment your average laptop battery would have. Are these things resilient enough to be bashed around?

    Are these capacitors only likely to be suitable for for small scale charges/discharges? Mobile phones? laptops? cars themselves?

    More questions than insights, I'm afraid, but I find it fascinating
    • Re:Fascinating (Score:3, Informative)

      by thebdj (768618)
      My guess would be pretty high. And after I type that I pretty much confirmed [] it. Besides, these things are microscopic in size (electron microscopes even). I would believe that by the time you were damaging these, you would probably already be doing some serious damage to the electrodes of the capacitor/battery.
    • Nanotubes are very strong. I'd imagine that if you're subjecting a laptop to forces strong enough to damage them, powering it will be the least of your worries.
    • And how long will the charge last on the battery if not used? How bad is leakage?

      I bet that is the best question to make.

    • charge density. (Score:3, Interesting)

      by Vexar (664860)
      The guy has a poster discussing uses such as electric car batteries, so I would say no. One part that bugged me in the "poster" [] is the energy density. A value of 60Wh/kg (is this gravimetric charge density?) is less than lead-acid. The power density is a whole lot higher at 100kW/kg, would someone care to explain the difference between the two?
      • Re:charge density. (Score:3, Informative)

        by jonored (862908)
        100kW/kg is the power density, i.e. a measure of how fast it can output a particular amount of power per kilogram of device.
        60Wh/kg is a measure of energy density, which is to say, joules per kilogram in a charged state - they are just using units of watt-hour, which can be more convenient for energy storage measurements.
        To put it into a normalised form, we have
        100,000 J/s*kg (joules per second per kilogram) for the power density,
        216,000 J/kg (joules per kilogram) for the energy density.
        So, one kilo of c
  • time to market (Score:3, Interesting)

    by yakumo.unr (833476) on Friday June 09, 2006 @07:55AM (#15501114) Homepage
    Thats just fantastic, sounds like the ideal replacment for batteries, and puts fuel cells out of business for small consumer products like laptops I'd have though, especially as they wouldn't cause any problems on planes.

    hydrogen fuel cells would still be great for larger things like cars.

    could these be produced in a way to fit in existing devices as soon as possible? I'f this really is safer for the environment, I'd love to see these asap, especially as most batteries are standard sizes already, even inside a laptop battery there are often (always?) muliple standard sized cells.

    I hope they're easilly recyclable too, for when they do finally fail.

    • hydrogen (Score:2, Interesting)

      by yakumo.unr (833476)
      actually, I suppose it could well be more environmentally friendly to just use these, if they can provide power on par with, or greater than fuel cells for size/weight. There wouldn't be any emissions with a capacitor? and weather you use fuel cells or these, there are power requirments to charge them/produce the hydrogen for their respective systems..
    • could these be produced in a way to fit in existing devices as soon as possible?

      TFA doesn't say what the capacity of his device actually is so I assume he has some kind of prototype but a NiCD replacement is a maybe for the future.

  • A good electric Car. (Score:5, Interesting)

    by jellomizer (103300) * on Friday June 09, 2006 @07:57AM (#15501122)
    With its longer life and faster recharge time. I wonder if this could lead to an electric car that is good for the masses where they can cross country and take only 5 to 10 minutes to recharge. That is the primary reason why the Electric Car never made popularity it is because it is not convenient enough for normal people.
    • The second challenge there would be a power infrastructure capable of supporting many thousands of fast recharges like that.
      • by timeOday (582209) on Friday June 09, 2006 @08:47AM (#15501335)
        The second challenge there would be a power infrastructure capable of supporting many thousands of fast recharges like that.
        The power supply to the gas station doesn't need to see the surges of power. The re-charging station could have an even bigger capacitor, which charges at a steady rate all the time. (Of course, even the average amount of electricity required would still be pretty big!)

        I wonder what one of these big capacitors would do in a crash? At least they're not filled with so many chemicals as normal batteries, but what would happen?

        • by Spirilis (3338) on Friday June 09, 2006 @10:01AM (#15501830)
          Yeah, this is a much better idea. That 'average draw', although high, could work out more favorably for the power companies because it would give them a stable power generation requirement, rather than wasting power or shutting off the turbines when there is no demand.

          Imagine the size of a megawatt-hour capacitor!
    • I could finally have my FLYING CAR? :-)
      • You mean the bits flying out of it after you smash it.

        One major difference between a capacitor and a battery is that the battery energy release rate on smashing it is limited by the rate of the chemical reaction. The energy release rate for this type of capacitor isn't.

        So the rigging charge cells into improvised bombs described in many Sci-Fi novels is just about to become a reality.
    • by MrSquirrel (976630) on Friday June 09, 2006 @08:49AM (#15501341)
      Another important thing about electric (battery) cars is that batteries perform poorly in the cold (due to their chemical electricity-generating process). Considering a good portion of the United States (and the world) is cold for a good portion of the year: this means battery cars are a no-no. A capacitor powered electric car, on the other hand, could operate in the coldest environments (well, except absolute zero) with little performance degredation (the lesser performance would be from moving parts in the car).
    • by pz (113803) on Friday June 09, 2006 @09:40AM (#15501680) Journal
      I wonder if this could lead to an electric car that is good for the masses where they can cross country and take only 5 to 10 minutes to recharge.

      Unlikely at best. The problem is that the rate of energy transfer for chemical storage (that is, fuels, like gasoline) is really, really high. While you could in principle build a station which could recharge your batteries in the same amount of time it takes to gas up your car, it wouldn't be something you'd want to be near.


      When you put gasoline in your car, you are moving power at a rate of about 5 MW. That's the entire output of a small power plant. Liquid fuels, gasoline in particular, are a very dense way to store and transport energy. Electrical wires aren't very good for that in comparison, even with superconductive cables. Think of it this way, even if we could transfer energy from a station to your car with 99.9% efficiency (which is well and far beyond anything we can do in the forseable future), that's 500 W of power that needs to be dissipated at the conversion site between the station and your car. That's going to be too hot to hold like a fueling nozzle for gasoline cars. If we use 48V to move 5MW (48V is gaining traction as a new standard for power transfer), that's 100,000 A of current. Even if we use an insane voltage level like 5 kV, prone to arcing and causing nasty things like fires and death, that's still 1,000 A of current. Not small. If this power is transferred by direct contact, you get immediate electromigration at the contacts, arcing problems when starting and stopping the current (ever wonder why power transmission towers are so tall?). If it's transferred by induction, then the EM fields will be enough to cause cancer (ok, I don't know that one for sure, but it's going to be as if 1000 microwave ovens are all operating right there at your car, something I don't want to be near).

      Building an electrical system that can move megawatts of power is not something that will ever happen on the consumer level.

      What about improving the efficiency of cars? We can make cars at best an order of magnitude more energy efficient. That isn't going to solve the problems alone.

      Now, if, instead of recharging, you swap out batteries (that is, move mass that carries energy instead of moving energy aone), things get far more attractive. Except that people are currently a little leary of exchanging parts of their cars (can you imagine swapping tires every time you went to a filling station?). But that would allow a quick recharging.

      The only solution that really makes sense for refueling by recharging is to do it while the vehicle is sitting idle when there is more time available, rather than being driven when there isn't. If you allow 20 hours for a recharge instead of 5 minutes, the power transfer rate drops to 20 kW which isn't so bad. Add in an order of magnitude higher efficiency vehicles and perhaps live with shorter distances between recharges, and you get down to the kilowatt range which is entirely doable (1.5kW can be supplied from a single, standard US household outlet).
      • by WhiplashII (542766) on Friday June 09, 2006 @11:18AM (#15502414) Homepage Journal
        Building an electrical system that can move megawatts of power is not something that will ever happen on the consumer level. No one will ever need more than 64KB...

        You realize that you have now committed the classic blunder (second only to getting involved in a land war in Asia). Millions of engineers are now scrambling to prove you wrong, at any cost!

        Here is how I would do it: Battery in car is a one meter square, 2 cm thick. Charging station brings over their one meter square battery, places it on top of yours. Power is transfered at 50 volts x 100,000 amps - but that 100,000 amps is flowing through a "wire" half a square meter in area, which is the equivalent of 0.1 amps through a somewhat standard 1mm wire. In other words: the efficiency is basically 100% (it would be hard to estimate before doing it, but very high); the grid can see a long slow charge (as the Charging station can slow charge their transfer battery); the energy transfer is done at 5MW, so it takes only a few seconds to fill your car.

        OK, I think you owe me lunch now!
    • by schmiddy (599730) on Friday June 09, 2006 @10:32AM (#15502052) Homepage Journal
      There's a good reason that we're not using high-voltage, large capacitors currently to run our electrical devices: price. (In addition to storage space, of course, but let's pretend the carbon nanotube thingy could take care of that). The potential energy stored in a capacitor, U, is defined by

      U = 1/2 * C * V^2

      Where C is the capacitance, in Farads, and V the Voltage. For comparison's sake, a typical 1.5 Volt AA battery is rated for around 2000 milliamp-hours (why they use this ridiculous measurement, I don't know, but it's all I can find). So a tiny AA battery stores the potential energy

      U_battery = 2000E-3 Amps * 1.5V * 3600 seconds/hours

      Or, it stores 11,000 Joules. Now, searching for big capacitors on froogle [], I came up with a link from Autotoys for a 1 Farad capacitor, on sale for a mere $42 (which is actually really cheap for one of those bad boys, but anyways..). It claims to have a "surge voltage" of 20V. So, assuming it's charged to 20V, the potential engergy in the capacitor is

      U_cap = .5 * 1 Farad * (20V)^2

      So this $42, huge capacitor stores 200 Joules, in comparison with our AA battery that stores 11,000 Joules. In addition to the problems of price, miniscule total energy storage, storage space (making impractical for electrical car use.. you'd need a TON to power a car for an hour.. 100 HP = 75kW, for an hour, that's 270 MJ.. that's a lot of capacitors), in order to get the most out of capacitors you have to charge to a very high voltage (since U goes up with V^2), so you need a high voltage DC power supply, and finally, unlinke batteries, capacitors' voltage goes down exponentially with time, so you need clever (i.e. large, complicated) circuitry get out a constant voltage from a capacitor bank.

      Basically, capacitors have their place (namely, smoothing voltages, or storing small amounts of power for quick discharge, i.e. camera flash), and batteries have theirs. The article is very light on specifics, but even if, say, the Cost / Farad goes down by an order of magnitude, and they manage to shrink the size as well.. I still don't see much changing. They also don't mention whether these things work at high-voltage. If they can't be charged up to 500+ Volts, they're not going to be able to store much energy. I'm not an expert on capacitor design, but if you look around for high-voltage capcitors (they go up to 10kV+), they pretty much all have tiny capacitances (e.g. 800pF, 10kV). I assume there must be some inherent difficulty in making them with both a large capacitance and high-voltage rating (or perhaps too dangerous.. who knows?). Don't get your hopes up just yet.
  • by spacerodent (790183) on Friday June 09, 2006 @08:00AM (#15501136)
    This is a really good plan in theory and on "cost is no object" plans it's a great idea BUT theres no real way this can replace batteries because your cost per unit is going to be much higher than standard batteries already are. No one is going to pay $20 for a pack of AAAs that you can get for $4 and just have to replace in six months.
    • by Andrewkov (140579) on Friday June 09, 2006 @08:14AM (#15501191)
      Aren't people already doing that with rechargable batteries?

      I'd gladly pay 4 times (or more) the price of regular batteries to have batteries that recharge in seconds and never need replacing. This will be great in cell phones and laptops, too.

    • I would pay 20 bucks for a pack of AAA batteries that had a life-span longer than the device I used them in and recharged in seconds instead of minutes. I don't know of any batteries that last 6 months (unless you mean they last 6 months in something like a tv remote).
    • On the contrary, if I have the option to buy a pack of two batteries for $20, or 4 for $4, and the two batteries will charge "in seconds" and last for hundreds or thousands of cycles, after just ten cycles I have "free batteries".

      I go through AAs very quickly because of my discman, I know I'd be interested at a $20 pricepoint.
    • No one is going to pay $20 for a pack of AAAs that you can get for $4 and just have to replace in six months.

      People already pay twice as much for lithium AAAs that are lighter and last longer. How much would people pay for something that you can recharge repeatedly for years to come, and that packs more power than a regular alkaline? Don't know, but there's probably a market if the price is "only" five times as much as regular batteries.

      And don't forget about using this tech in your iPod or other porta

    • If you use your math, the two power sources are equivalent so long as whatever being powered lasts 2 1/2 years. It also fails to account for the fact that batteries come in many different stripes that match different needs - cell phones, watches, cars, etc. The world of batteries is not defined by AAA and surely there are applications where this new tech would be perfect.
    • by Jasin Natael (14968) on Friday June 09, 2006 @08:40AM (#15501300)

      ... And thus the comments about the mfg. process 'catching up'. I think we already don't use Li-Ion AA's and AAA's because they're cost-prohibitive, and the packaging is wasteful of space. I already wince at paying about US$2.50 per individual AAA for NiMH. But this technology promises features I think are worth paying for, just like having Li-Ion and Li-Polymer batteries in your cellphone, mp3 player, and PDA right now. Imagine when the battery for your cellphone or iPod is long-lived enough to be printed onto the circuit board and never replaced, and it can receive a charge in only a few seconds. If this is done properly, it'll eventually be the end of removable cells altogether.

      This even opens up a lot of integration possibilities that just weren't there before, like peripherals that bring their own capacitor bank in to boost the system's capacity. Everything with a PCB can now cache its power, without all the bulk of a traditional battery. Imagine expansion cards that can carry the power needed for I/O (Wireless, Flash Memory, whatever) and charge with the system. You could even use the memory expansion slot as an auxiliary battery, like on some laptops how the optical drive can be replaced with another battery.

      Take this with System-On-Package designs like were just recently discussed here, and we may get some really small electronics in our lifetime. You could even reduce capacity to save space -- I wouldn't mind charging my cellphone almost every night if it only took a few seconds.

  • by HawkingMattress (588824) on Friday June 09, 2006 @08:03AM (#15501151)
    Summary says this technology would allow batteries to charge faster. It's a big understatement since the article says they would only need a few seconds to be fully charged...
    • they would only need a few seconds to be fully charged
      That's very unlikely, assuming that these capacitors can reach the power densities that current NiMh cells can.
      The current needed to charge them so fast is tremendous, the cells would explode.
      For example, for a AA cell of 2000 mAh, you would need 720 Amperes to charge in 10 seconds, or 1.44 KA to charge in 5 seconds.
  • by theonetruekeebler (60888) on Friday June 09, 2006 @08:05AM (#15501157) Homepage Journal
    I have a couple of concerns about the safety and durability of nanotube capacitors, particularly if they are to be used in portable equipment.

    First, safety. One of the amazingly cool things about capacitors is that they can deliver all their charge over the course of a few milliseconds. This makes them very useful for things like strobelights and subwoofers. But it can be very, very dangerous: What happens if you drop your in the toilet? Or you drop your iPod and it gets run over by a car? If they have batteries, a short circuit will cause the battery to get warm for a while, or it will release some slightly caustic goo and you have to wash your hands. But if they have capacitors, you get an explosion and a violent electrical arc.

    Second, durability. You can beat the hell out of a chemical battery, expose it to shock and vibration to no end and it will continue to operate. These nanotubes, OTOH look awfully easy to break. Breakage could cause two things to happen: loss of capacitance, or worse, an internal short circuit, and see above.

    It will be interesting to see how these two problems are addressed, or if these cool toys will be relegated to industrial and other controlled-environment applications.

    • Uhh... nanotubes easy to break? Since when? They're the only material strong enough for a practical space elevator! Think a bit about that.
    • Nanotubes are extremely strong.

      As for safety, just like Li-Ion batteries have safety devices, I would imagine a "batacitor" would probably have a current limiting device inside a casing of adequate strength (and waterproofness), so the current draw from exposed terminals couldn't reach dangerous levels.
    • by marcosdumay (620877) <> on Friday June 09, 2006 @08:27AM (#15501248) Homepage Journal

      You have never created an internal short circuit on a conventional (rechargable) battery, did you? It is also able to deliver all the stored energy on an explosion that will take your hand away.

      Now, batteries don't explode all the time, because they are well blinded. Capacitors are less dangerous (carry less energy), so they are not that well blinded, and explode often. There is nothing stopping the people from making blinded capacitos out of economics, and it could be even safer than battteries, because there is no ion trading going on.

    • by Grab (126025) on Friday June 09, 2006 @08:28AM (#15501252) Homepage
      If they have batteries, a short circuit will cause the battery to get warm for a while, or it will release some slightly caustic goo and you have to wash your hands.

      Sorry, that's incorrect.

      Try shorting a car battery with a screwdriver and tell me there isn't a violent electrical arc. Also, NiCads (and I believe NiMH) have very low internal resistance - if shorted, they can literally explode as they overheat dramatically. You're confusing this with non-rechargeable batteries, which behave as you describe.

      Also, capacitors deliver charge at a rate dependent on the impedance of the load they're driving. It would be very straightforward to put a small resistor in the package containing the capacitor, so that the current out of it is limited.

      Regarding the short-circuiting, capacitors require overlapping surfaces that are electrically insulated from each other. That means if you're using nanotubes, you'll want both sides covered in nanotube "fuzz" and the two sides then pushed together so that the two intertwine. This means that one (or preferably both) sides need their nanotubes coated with some kind of insulating material for it to work, otherwise the nanotubes will simply short out, and then you won't have a capacitor any more. And that means you won't get short circuits from random broken nanotubes in the structure.

      Fragility I don't know about, but since carbon nanotubes are the strongest substance currently known, I suspect it's not going to be a huge problem. Also consider that the whole thing could easily be encapsulated in some solid insulating block so that it's a single physical chunk (remember that carbon isn't a metal so there are no significant expansion/contraction issues with heat). Batteries are only as solid as they are because they've got a solid metal case encapsulating well-packed electrodes and electrolyte - try dropping a plastic-case car battery from a height and tell us how solid it is. :-/

      Given how desperate battery manufacturers are for any kind of edge, I imagine this will be rushed to market as fast as physically possible!

  • Yeesh... It switches between the terms battery and capacitor like they are interchangable. It's really annoying because in one sentence they use capacitor and then in the other they use battery. Battery stores energy using chemistry while a capacitor stores energy in electric fields.
  • Capacity? (Score:3, Insightful)

    by stixman (119688) on Friday June 09, 2006 @08:09AM (#15501174) Homepage
    TFA says nothing about what kind of capacity improvements we're talking about here. Can anybody offer some insight? What kind of a charge will they be able to hold compared to today's chemical equivalents?
  • Are they safe ?!? (Score:2, Interesting)

    by ctrl-alt-canc (977108)
    Some time ago a 10 uF capacitor in a PSU exploded close to my face while servicing a PC. Luckily the PSU box was pretty well robust, and I had no injuries at all, but I'll remember for ever the loud BANG that followed (with a lot of smoke). I wonder if the same could happen by misfortune with one of these devices. AFAIK cellphone batteries seldom explode, so I am not so sure if capacitors would be a safer alternative.
  • by spectrokid (660550) on Friday June 09, 2006 @08:12AM (#15501183) Homepage
    Capacitors also have another difference: they can be (dis)charged extremely quickly. That means you will be able to recharge very quickly (if you have a spiffy charger), but I wouldn't want to drop a capacitor powered cellphone in the toilet.....
  • by Frightened_Turtle (592418) on Friday June 09, 2006 @08:17AM (#15501203)
    Really, the true test will be if it can handle the load of a Hello Kitty Vibrator [].
  • This Citizen watch [] is solar-powered and stores electricity in a capacitor rather than a battery. The capacitor rumoredly wears out after 5 years or so (hence, the warranty only lasts that long...).

    It's a great watch, BTW, for anybody looking for a decent new watch. :-) (If you're ridiculously-loaded and/or exceptionally-generous, it'd make a fine father's day gift I'm sure.)
  • Energy Density (Score:2, Interesting)

    by gatzke (2977)
    The problem with capacitors is energy density. They can charge and discharge quickly, but the amount of energy per unit volume or per unit weight is usually not very good, even compared to batteries.

    New supercapacitors (existing term, really) will improve the energy per weight or energy per volume, but they may cost more (energy per dollar).

    If this is cheap and hig density, it could be a great step forward.

    PS, check out the powerlabs guys. They do lots of dangerous stuff with bit caps
    http://www.powerlabs. []
  • by hal2814 (725639) on Friday June 09, 2006 @08:20AM (#15501220)
    My experience with capacitors is limited but I do know that they are extremely dangerous. I do distinctly remember having to discharge the capacitors in my arcade monitor in order to replace some circuitry. This involved a screwdriver with a grounded chain soldered onto it, some rudder gloves, and some flinching like a little school girl when you hear that loud pop from the discharge. I'm not entirely certain I'd want this sort of thing powering my laptops and cell phones.
  • by jdoeii (468503) on Friday June 09, 2006 @08:23AM (#15501230) Homepage

    Seems like I miss something. It's not the area of the capacitor that matters (yes, I know the formula C=A/d for flat electrodes) but an "effective area". These capacitors are supposedly two flat or nearly flat substrate surfaces each coved with nanotube "fur". There is a gap between these two electrodes. The gap is much larger that the thickness of the nanotube. Consequently, the effective area of the capacitor is not much larger than the area of the flat substrate electode. What's the advantage of the "fur"? I would understand if [+] and [-] charged nanotubes were alternating inside the fur, but it's clearly not the case judging from the picture.

    For instance, take a wire, cut it in half and separate two pieces by a small gap. That's a capacitor. Its capacitance is going to be somewhat larger than the A1/d where A1 is the area of the wire crossection, and a lot smaller than A2/d where A2 is the full surface area of the wire. The same applies to nanotubes.

    So, obviously, they are doing it differently. How?

  • There's a limit (Score:3, Interesting)

    by Anonymous Coward on Friday June 09, 2006 @08:24AM (#15501235)
    The capacitance isn't just a function of raw surface area. If that were the case, you could double the capacitance just by roughing up the surface of the capacitor plates. The contribution of any spot on the surface depends on the area of that spot and the distance between it and another oppositely charged surface as well as the dielectric constant of the material between the plates. You can increase the surface area as much as you want but you still have to get the surfaces to line up with each other.

    It is hard to exceed a certain energy storage on a capacitor. As you move the plates together, the capacitance goes up and you can store more charge per volt. The breakdown voltage goes down as you move the plates together. So you can store a small charge at a high voltage or you can store a large charge at a low voltage. For a capacitor of a given volume, you can store only so much energy depending on the breakdown voltage of the dielectric material.

    I don't doubt that you can double or triple the energy storage of capacitors compared with current technology. On the other hand, I am very skeptical about the possibility of getting enough capacitance to store enough energy to be a general purpose battery replacement.

    I leave it to you as an exercise to calculate the capacitance of a 2 volt capacitor necessary to store one amp hour. ie. something similar to an AA battery cell.
  • Real-world example (Score:5, Interesting)

    by Marillion (33728) <`ericbardes' `at' `'> on Friday June 09, 2006 @08:45AM (#15501324)
    I used a 1989 vintage computerized stage lighting control console used a big capacitor soldered to the back of the PCB to hold the settings in RAM while the unit was switched off. Typically, the capacitor could hold a show for about three to four weeks and every time it was switched on, the capcitor would recharge. It still had a "modern" 720k floppy disk just in case.
  • by Eivind (15695) <> on Friday June 09, 2006 @08:52AM (#15501356) Homepage
    I find it suspicious that no mention is made of the achieved energy-density in these experiments, other than that it's "higher" than conventional supercaps.

    The thing is, one kg of petrol holds around 45MJ of energy. One kg of NiMH batteries hold around 0.25MJ, a factor of almost 200 less. A lead-acid battery holds half that. A normal capacitor holds 0.002 MJ/kg.

    So, even to compare with lead-acid batteries in energy-storage this thing needs to be 50 times better than normal capacitors.

    Recharging in seconds is fine, assuming you can build a sensible car that goes oh say 100 miles at the least between recharges, that's perfectly acceptable for most people. Same for cellphones; faster recharging is very nice. But only if you can still go for 2-3 days without recharging, and talk on the phone for atleast an hour or two before its empty.

    A car that could only go 20 miles between recharges would not be a hit, not even if the recharge was done in a minute.

    • by Anonymous Coward on Friday June 09, 2006 @09:42AM (#15501696)
      The real information can be found in df [] It lists project goals as 300,000 cycles and 60 Wh/kg (Which if I used the units program correctly is 0.216 MJ ar almost as much as a NiMH battery.)
    • From TFA:
      Schindall says, "Small devices such as hearing aids that could be more quickly recharged where the batteries wouldn't wear out; up to larger devices such as automobiles where you could regeneratively re-use the energy of motion and therefore improve the energy efficiency and fuel economy."

      He doesn't say it will replace the main battery of a hybrid car. The bulk of gas mileage gain of such car comes from the regenerative braking. Gas engine running at constant optimum RPM and load is another, smalle
    • I don't think it's suspicious that the article doesn't talk about energy density. Such articles rarely contain any real details.

      If you go to and track down their version of this story you'll find the blurb below. It still doesn't say comparable energy density, but at least it says comparable amounts of energy.

      More worrying to me is the dreaded "five years away".

      A Better Energizer
      An ultracapacitor is what really keeps going and going. . . .
      By Alex Stone
      DISCOVER Vol. 27 No. 05 | May 20

  • Supercapacitors (Score:4, Informative)

    by 15Bit (940730) on Friday June 09, 2006 @08:59AM (#15501401)
    These are just supercapacitors - a device designed to bridge the gap between batteries (which store energy chemically) and capacitors (which store energy as an electric field). The idea is not new - for decades people have wanted to combine battery type capacity with capacitor discharge characteristics.

    However, there is now a lot of academic and business interest in them as they are ideal for a wide range of modern applications. Devices like UPS's and power smoothers still run on lead acid batteries, which are bulky, contain corrosives and are prone to unexpected failure (at least mine seems to be). There is also a big push from the electric vehicle crowd. Note though that they are unlikely to form the primary power source for an electric vehicle (they still have poor energy density compared to chemical technologies), but are extremely attractive for both initial power-up (i.e. heating a fuel cell to running temperature) and for sensible implementation of regenerative braking - charge the supercap when you brake, use the energy for short term bursts (driving up a hill, overtaking etc).

  • by ab762 (138582) on Friday June 09, 2006 @09:12AM (#15501476) Homepage
    At the very beginnings of electricity, it was stored in Leiden Jars [], a form of capacitor. In the 1930's, the accumulator, a form of capacitor, was sometimes used to power early radios. Apparently, you used to carry these back to the shop to have them charged up.
  • by necro81 (917438) on Friday June 09, 2006 @09:29AM (#15501602) Journal
    The promise of replacing your computer battery with a capacitor that recharges in a few seconds probably can't happen all that time soon.

    Some math to back this up: My work laptop, a Dell Latitude D610, has a 53 WHr battery. My home laptop, an Apple 12" Powerbook, has a 46 WHr battery. These aren't huge laptops, mind, and battery capacity is only on the rise as consumers demand more.

    Let's use the Dell example, 53 WHr. Change hours to seconds, that's 53 * 3600 = 190,800 Watt-seconds (more usually known as Joules). 191 kJ - that's a fair bit of electrical energy to store, either in battery or in capacitor form. Let's ignore losses that occur in the charger and energy storage device - assume everything is 100% efficient for a moment.

    What if we wanted to charge up that 191 kJ capacitor in, say, 10 seconds. That would require a 191 kJ / 10 s = 19.1 kW power supply. Hmmmm, don't think we'll be seeing one of those in a laptop bag anytime soon.

    Laptop batteries are a particularly high-energy example, but it illustrates the kind of power increases you'd need to accommodate if instead of charging in hours, you charged in seconds. If you had a battery that used to charge in, say, one hour (cellphone, PDA, whatever), and you instead wanted to charge it in (again, for example) 10 seconds, the charging power supply would need to put out 360x more power. Even to charge it in a minute would require a 60-fold increase in power. That'd be an amazing and fascinating power electronics problem to consider - how to make such charging devices as compact as today's.
    • by Anti_Climax (447121) on Friday June 09, 2006 @12:16PM (#15503029)
      While your math is sound as is the point you bring up I'd like to add to it if I can. You have to realize that not every application of these capacitors will require a 10-60 second charge time. For the laptop example most people would be exstatic if they could recharge their laptop from dead to full in 5-10 minutes, which would only require a 300-600 watt power supply. I'm sure that would be bulky but not unreasonably so for and external supply with the ability to charge that quickly.

      The real gotcha is that the charge power is not anywhere close to constant like the first 80% of a charge to a conventional battery. Within the first 20% of the charge cycle you'll have pushed 2/3 of the total power that cap is going to draw if it's readily available. With that in mind they'll probably have a built in cut-off similar to those used in Li-Ion batteries that prevents the cap from discharging below a certain point. which would certainly limit the available power but lessen the demands during charging.

      So basically if we want charging in seconds like the article suggests, we're working with overly large power requirements and/or diminished capacity. If we want minute scale chargnig we're looking at diminished capacity and reasonable power requirements.

      There's also competition with newer Li-Ion and LiPoly configurations which, through the use of nano-tech as well, to give us 80% charges in 5-10 minutes. There are also quick-charge NiMH solutions already on the market which can pack about 40,000 joules into 4 cells in 8-15 minutes and are scalable to laptop level battery configurations.

      I don't think this is going anywhere for a while, but it could end up with some use in industry eventually. And I certainly like the idea of large cheap caps even if they won't replace batteries any time soon.
  • by StoneCrusher (717949) on Friday June 09, 2006 @09:32AM (#15501623)
    This tech would be excellent for cars...

    Imagine refulling your car by simply stopping at the traffic lights. A swipe system like the toll roads handles payment, and your off again. It would not be hard to have a recharge every 50 - 100km on the highway if they aren't manned. Just a drive though pitstop - and your back on your way.

    Who cares if electric cars don't have huge range if recharge stations are everywhere. And if your a "but I like to spend 4 days driving in the wilderness", then you take extra storage... just like you do with petrol.

    Oh,... and it would not be hard to fix the complaint about exploding capacitors... Seal them in plastic so there water tight. Only two wires in/out... A very small amount of circuitry would allow high current in for recharging, and have a current limiter on the way out. Not crush proof, but certainly water/short circuit/toddler proof.

"But this one goes to eleven." -- Nigel Tufnel