• Dec 1st 2010 at 4:00PM
  • 36
In the coming decades, hybrids, and maybe even all-electric vehicles, may cruise without batteries. Instead, the energy in these vehicles of the future will be stored in a supercapacitor which could be recharged in minutes, possibly seconds. We've heard of the potential of supercaps (and ultracapacitors) before, but researchers have just announced they've overcome an obstacle to this device development. In the lab, they have developed supercaps with an energy density equivalent to that found in the nickel metal hydride (NiMH) batteries used in hybrids today. Using more technical language, they claim a nano graphene-based, ionic liquid-enabled supercapacitor has achieved a specific energy density of 85.6 Wh/kg at room temperature. I'm sure I speak for all of us here at ABG when I say, "Wowsa!"

The team, consisting of members from Nanotek Instruments, Angstron Materials and the Dalian University of Technology in China, originally discovered that graphene sheets could be used as a supercapacitor electrode back in 2006. However, the one-atom thick material had a tendency to "restack" itself, which interfered with the necessary ionic fluids (of course!). The researchers have now learned that by using curved graphene sheets instead of the original flat sheets, that problem is avoided and capacitance is greatly improved. No word yet on when the tech might be commercialized or what further energy density gains might be possible, but we suspect we'll be seeing graphene-based supercapacitors for a variety of applications before too long. Thanks to David for the tip!

*UPDATE: We reached out to Bohr Jang of Nanotek Instruments for further information. He speculates commercialization could happen within three years. They also hope to improve the energy density to 100-150 Wh/kg.

[Source: Physics World]


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    • 1 Second Ago
  • 36 Comments
      • 2 Years Ago
      Divide their stated capacity which is likely based on carbon content by 5 to get the capacity of the cell.
      • 4 Years Ago
      Correct me here if I'm wrong here:

      85.6Wh/kg = 38.7Wh/lb

      The current Tesla Roadster stores 53kWh with a battery pack weighing 995lbs.

      53,000Wh / 38.7Wh/lb = 1370lbs for the same charge.

      So the real benefit isn't weigh savings but rather charge time ONLY?

      I guess I'm OK with that if companies start to shed the poundage.
        • 4 Years Ago
        and cycle life.
        if you imagine a tesla roadster with the same 450kg pack but with a bit smaller capacity in the form of supercapacitors, then you have maybe 235km range (vs 340) but you would be able to put back the 235km in the tank in a couple of minutes. a pack that would never die AND a pack that could deliver multiple megawatts of power.
        with the right infrastructure that's a lot more interesting vehicle.

        that said though, the tesla pack's effective density is only 125Wh/kg. in the future it is conceivable/expectable to have 350Wh/kg lithium batteries at which point 86Wh/kg supercaps are not as obviously interesting.

        but that said, noone is saying that the 86Wh/kg achieved here is the limit..
        should practical supercaps reach 200Wh/kg then it is basically unimportant how high conventional batteries go because a slow charge 1500km range is not really better than a 400km blitz charge range with a pack that never needs replacement.

        and carbon we have plenty off. I suggest we melt down republicans and tea party members and use their carbon. let's start with Lou Dobbs : )
        • 4 Years Ago
        Pretty much yes, ultra capacitors are not actually good for energy density, not nearly as much as batteries. They are good for power density.

        The difference here is (as referenced above), that you can drain and charge them much more quickly. So they may hold only 1/10th as much power per unit volume (if that), but they can release the power they do have 100x quicker, so they can produce a lot of power (for a short time) from a small pack.

        In addition, ultra capacitors are leaky enough (lose charge) that with large scale use of them, you could be looking at losing a countable amount of power sitting in a parking spot overnight or during the day while you are at work. This not only means you get less range than you thought if you let the car sit before driving, but it can cost you money. If it costs you $5 to fill your car each day and the pack loses 10% of its power just sitting around, you're throwing $0.50 a day out the window, or $150/year. ($5 is about enough power to fill a Tesla Roadster, a Leaf would be more like $3).
        • 4 Years Ago
        Actually it makes more sense to compare it to cell density which is about 175Wh/kg (the Tesla spec you are giving is the pack density), which makes super-caps lose even more. The original article says the density is comparable to nimh batteries, not li-ion.

        However the main advantage like Dan said is much higher power density, allowing incredibly fast charges, and also potentially unlimited life. Even if the density isn't enough for mobile applications, it could be huge for stationary applications, esp. for grid leveling and also for buffering rapid charge stations.
        • 4 Years Ago
        See the above discussion. Capacitors won't be used for mass energy storage, but as a power boost and temporary store making use of their high charge/discharge capability.
        • 4 Years Ago
        Damn Dan,

        You really are a piece of s*)# aren't you? You disagree with someone, so you want to kill them.
      • 4 Years Ago
      These capacitors are very sensitive to temperature when it increases, and at higher than room temperature can store much more than 85.6Wh/kg:
      'Researchers from Nanotek Instruments and Angstron Materials have developed a graphene-based supercapacitor that exhibits a specific energy density of 85.6 Wh/kg at room temperature and 136 Wh/kg at 80 °C (all based on the total electrode weight), measured at a current density of 1 A/g.'

      http://www.greencarcongress.com/2010/11/liu-20101126.html#more

      What we don't know is if the capacity plummets a lot further at low temperatures, say at -10C.
      If that is the case then the capacitors would need insulation to keep the energy density up.

      I'd see these as a supplement to lithium batteries, which can hit around 250Wh/kg or so, rather than a replacement.
        • 4 Years Ago
        @ paulwesterberg:
        In this case you're talking about graphene which is an unsurpassed conductor within normal temperature range (100 x + better than copper). Power losses are extremely low and I wouldn't bank on the fact that those heat losses are sufficient to heat the capacitor and hence improve its capacity.
        • 4 Years Ago
        Insulation doesn't work that way. Insulation only slows down thermal transfer rates. If you want something to stay warm when its in a cold environment, you need to spend energy heating it. Insulation just reduces the amount of energy you need to spend.

        People think insulation makes things warm because it helps people keep warm. The reason for that is people generate their own heat. If you put an insulator on something else, say a battery or a can of pop and then put it outside overnight, it will be at ambient when you check on it the next day, even though you have insulated it, just as if you hadn't.

        I agree there's no way these can match batteries right now. Both because of density (which is measured against weight here, not volume, the light weight of caps helps make that look better) and because caps don't hold energy long term as well as batteries do. Batteries will leak a few percent a day, an ultra capacitor can leak that much in an hour.
        • 4 Years Ago
        @Chris M:
        We haven't really been given enough information to work out exactly what is going on.
        Perhaps if the temperature drops they self discharge, which could be rather nasty depending on how rapid it is, as the capacity they give at room temperature is around 63% of that at 80C, so a 24kwh capacitor bank would loose perhaps 10kwh if the temperature dropped to ambient, so I would not fancy being in the vicinity if it happened quickly.
        OTOH, I was assuming that this mainly refers to the capacity when you charge it up, so if you do so under 80C conditions you get much more than at room temperature, but it would only gradually loose the charge if the temperature dropped, especially as you say because the discharge itself creates hear.
        LS tells us that the ability to hold charge of capacitors is anyway limited, although again we don't know if these new capacitors are as limited as the present ones.
        It's an interesting new avenue anyway.
        • 4 Years Ago
        I think that initially(as maximum energy density lags lithium) we will be using capacitors as a short term energy cache for regen/launch.

        That way you can store as much more energy during regen and save the primary battery from doing a lot of additional charge/discharge cycles. This would lengthen the lifespan of your battery and allow improved vehicle efficiency, performance & maximum range.
        • 4 Years Ago
        @LS2LS7
        If you store you car in a garage heated to a temperature of 50F during the winter and insulate the capacitors the insulation will maintain that temperature after the car leaves the garage. Insulated capacitors will also warm themselves as they are used and small amounts of energy are wasted as heat.
        • 4 Years Ago
        If the capacity declines with declining temperatures, then presumably it "self discharges" during a temperature drop, that self discharge would itself produce heat and slow the temperature drop.

        The energy density still isn't as good as the best LiIon batteries, and even the hoped-for improvements will still fall short. There will be many practical uses for such ultracapacitors, but not as the primary energy storage for plug-in vehicles.
        • 4 Years Ago
        I was being lazy using the term insulation to stand in for a temperature controlled capsule, which might involve heating, at any rate to kick it off in cold weather.
        However fuel cells generate heat in operation, so insulation should be able to do most of the job once they are running.
      • 4 Years Ago
      Meh ... I think I am going to wait for the flux capacitor
      • 4 Years Ago
      ThermaBlok: The 21st Century Revolution In Aerogel Building Insulation

      http://thermablock.com/index.html

      "You could take a two or three-bedroom house, insulate it with aerogel, and you could heat the house with a candle. But eventually the house would become too hot."



      http://www.ecogeek.org/architecture/2524

      ...Specialty panels with significantly higher performance are available. Vacuum boards can provide as much as R-30 per inch. And a company called Glacier Bay offers Barrier Ultra-R panels, which use aerogel inside a sealed, evacuated panel. Ultra R panels offer R-50 per inch insulation value, roughly 10X better than a conventional polystyrene or polyiso insulation board.

      By incorporating the aerogel core inside the vacuum panel, the panels require a less extreme vacuum to obtain their insulation performance. And the reduced pressure differential due to the lower vacuum level translates into a longer life for the panel. A typical panel needs to have internal braces to keep the panel from being crushed by the outside atmospheric pressure (and these braces reduce the effectiveness of the vacuum insulation by acting as a thermal bridge that lets heat move from one side to the other). Aerogel is a very strong material, and supports the panel faces to prevent them from being crushed.

      Even if the panel is punctured and the vacuum is lost, these panels will continue to perform at R-9 per inch, still nearly double a conventional insulation board. And the panels carry a 25 year warranty.

      harlanx6
      • 4 Years Ago
      Eestor, the Chinese are going to kick your lame ass!
      • 4 Years Ago
      I am still wondering what kind of range might be possible if you used both a super capictor aswell as a tradiotnal (if thats possible) battery pack setup have the battery's continue to pump up the capictor as a range extending device. That way even of you can top up for short trips in seconds its nice to have all that extra juice to keep going.
      • 4 Years Ago
      Let's not forget about the cost factor.

      Li-ion batteries are still VERY EXPENSIVE.

      From the graphene production process described in the Rice paper, graphene sheets will be possible to produce quite cheaply once the specific production equipment is developed and mass production starts.

      Even if the graphene capacitor has worse real-life usage characteristics than batteries, vehicle producers would deploy them in every slightly viable scenario because of the cost factor.

      Even in the worst case scenario, graphene capacitors could improve the power characteristics of batteries (e.g: 1/3 capacitor, 2/3 battery hybrid units).
      • 4 Years Ago
      We also have to remember that Ultracaps can use 100% of the stored energy w/o degradation.
      Remember that the Volt is (or maybe was) going to only use 8kWh of the the total 16kWh.
      So if the Volt used these SuperCaps, which have about half the energy density of Li Ion, it would still essentially weight the same.
      • 4 Years Ago
      I'm always highly skeptical of these kinds of announcements, because we've been burned a lot of times. It seems like every time some researcher finds an effect they can create in the lab, that they imagine could hypothetically be applied to energy storage, somebody in the press goes nuts with a story about how Revolutionary Super-Mega-Capacitors/Batteries are right around the corner. Dig a little and it usually turns out to be a tiny, hypothetical baby step towards something that might or might not ever pan out.
      • 4 Years Ago
      The Toyota Rav4EV uses Ni-MH batteries with about the same energy density.

      Sure it is a bit heavier to get the same range as a Lithium Ion EV... but look at it this way:

      A Li-ion pack with 140 wh/kg could only use about 80% of it's capacity to achieve longevity. That is about 112 wh/kg of useful energy "to be discharged" from the pack. And with discharge losses at about 90%, that is ~100 wh/kg of useful energy to the motor controller.

      While an ultracap would use 100% of it's capacity AND with almost zero losses for discharge, 85 wh/kg is exactly what you get to the motor controller.

      Yeah, still 15% less range for the same weight of the pack.

      **But what about NOT needing a Battery Management System (BMS) like you would need if you have a Lithium ion pack?

      *** And having 15% less range would be just fine for most people if they could fast charge within 5 minutes.

        • 4 Years Ago
        Fast charge in seconds more like and fully charge in under 2 minutes....wowzers

        Perhaps the Supercap could provide a small range for supplement like in a hybrid and provide most of the 10-20mile driving we do and save the main battery from wear and tear in day to day use and charging, then the battery kicks in for longer journeys and uses the capacitor to regenerate a few spare miles from breaking
        • 4 Years Ago
        @Joe,
        there is an erudite discussion of the practicalities of taking capacitors down to near zero charge here, in a comment by MG:
        '"A supercapacitor can be discharged down to zero without damage..."

        In theory it's true, but don't forget that voltage of capacitor drops during discharge process. Li-Ion batteries (and I guess Li-Po ones) voltage drop per cell maybe from 4.0 Volt to 3.4 Volt, as SOC goes from 90% to 20%. Depends on technology, those from EnerDell had lower value, would drop to 1.8 V.
        Energy contained in capacitors is given by formula: W = 1/2 C* V^2.
        This applies to linear capacitors, ie where capacitance is voltage independent, but we don't know almost anything of these graphene capacitors.
        So when voltage drops to 50%, only 25% energy remains.
        When 80% energy is used up, voltage drops to 45%.
        In order to handle the widely variable input voltage, more complex (and expensive) power electronics is needed.
        How far low (in voltage terms) to go, will be dictated by the price of installed capacitive storage and extra cost for wide-range power converter.'

        http://www.greencarcongress.com/2010/11/liu-20101126.html

        It's all a bit above my head, but it probably makes more sense to you.
        To me it sounds as though the ability of capacitors to go down to near zero charge is a bit Cole Porter - it ain't necessarily so! ;-)
        • 4 Years Ago
        It might not need "battery management", but it does need a sophisticated buck/boost circuit to compensate for the changing voltage, and that circuit would limit the efficiency of charging and discharging.
      • 4 Years Ago
      Erm, what's that graph supposed to mean anyway? :P

      "The device might be used to recharge mobile phones, digital cameras and micro-EVs"

      Yepp.. remember, readers. This ain't a battery.

      Supercapacitors do have a lot of advantages and uses, however. They can be used to store regenerative braking energy, increasing the amount of power that can go back in to the hybrid battery.

      They can be buffers for wind or solar power. If they end up being cheaper than batteries, they could drastically reduce the cost + increase the effectiveness of green energy installations.

      These could potentially make the size of the motor controller package smaller also.

      Interested to see if this one bears fruit.
        • 4 Years Ago
        The graph shows the relationship between energy density and power density with these newfangled ultracaps. Note that the higher power output version stores less energy per Kg., and the higher energy ultracaps have a lower power output. I suspect the reason is that more current carriers are needed for higher power, thus adding to the weight but not the energy storage.
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