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Supercapacitors are slowly emerging as novel tech for electric vehicles

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A couple years ago Tesla CEO Elon Musk said in an offhand remark that he thought capacitors — rather than batteries — might be the energy storage tech to deliver an important breakthrough for electric transportation. Tesla cars, of course, use lithium ion batteries for storing energy and providing power for their vehicles, but Musk is an engineer by nature, and he likes what ultracaps offer for electric cars: short bursts of high energy and very long life cycles.

Capacitors are energy storage device like batteries, but they store energy in an electric field, instead of through a chemical reaction the way a battery does. A basic capacitor consists of two metal plates, or conductors, separated by an insulator, such as air or a film made of plastic or ceramic. During charging, electrons accumulate on one conductor, and depart from the other.

A bus using ultracapacitor tech from Maxwell, image courtesy of Maxwell.
A bus using ultracapacitor tech from Maxwell. Image courtesy of Maxwell.

Supercapacitors also have two metal plates, like capacitors, but they’re usually coated with a spongelike, porous material known as activated carbon. The porous material makes the surface area a lot larger and boosts the energy density. They’re also immersed in an electrolyte made of positive and negative ions dissolved in a solvent. Finally, each of the ultracapacitor’s carbon electrodes ends up having two layers of charge coating its surface. Ultracapacitors and supercapacitors are often used interchangeably to mean the same thing — basically, a double-layer capacitor.

According to an article in the Economist this weekend, super and ultracapacitors are already starting to be used in a variety of novel ways in electric vehicles, including in racecars and also in some buses, trams and trains. Ultracapacitors are often used to aid batteries in hybrid and electric cars, something we’ve covered over the years.

One of the more common uses of ultracapacitors is in hybrid buses in China. Many of the buses there are equipped with stop-start engines (which turn off when the vehicle stops) and the ultracapacitor is used to turn the engine back on, thus reducing the load on the battery itself. Maxwell Technologies is a significant supplier of these start-stop engine ultracapacitors. China also has a half-dozen trams that are using ultracapacitors to efficiently charge up between stops.

Paper Battery Company's ultracapacitor tech demonstrated in an iPhone, courtesy of Paper Battery Company.
Paper Battery Company’s ultracapacitor tech demonstrated in an iPhone, courtesy of Paper Battery Company.

One of the more fun uses of ultracapacitors in electric vehicles is as a way to provide a short burst of power for racecars. Toyota has a hybrid racecar called the TS040 (pictured in the thumbnail), which uses a supercapacitor to add an additional 480 horsepower. The TS040 also has regenerative braking, which recharges the supercapacitor. Toyota is using what it’s learned with the TS040 in a concept car called the Yaris Hybrid-R, which uses a supercapacitor.

Beyond electric vehicles, ultracapacitors could play an interesting role in ultra-thin battery-powered devices and gadgets. A team out of Singapore has developed an ultracapacitor based on graphene and carbon nanotubes that can be woven into clothing, opening up applications for wearable devices. A startup called the Paper Battery Company has created a thin ultracapitor sheet that can be wrapped around the battery in a cell phone to squeeze out extra energy and help a cell phone last longer.

The biggest drawback of ultracapacitors for energy storage is that they’re just not as energy-dense as lithium ion batteries and other types of batteries. But the Economist notes that newer ultracapacitors are getting much better energy densities and a new hybrid supercapacitor has recently reached 30 to 40 percent of a lithium-ion battery’s energy density.

45 Responses to “Supercapacitors are slowly emerging as novel tech for electric vehicles”

  1. Here’s my contribution. Its been on my mind for years Mr Elon Musk.
    How about some acreage devoted to supercapacitor grids for storing lightning? I think it would almost be laughingly simple to create something with an overload dump of some sorts. You could say the technology has been there since the beginning of time but nobody in any sort of fuel business would tolerate storing lightning. They’re too stupid to figure it out and far more intent on destroying the earth than they are perceived to be.

  2. Ray Anderson

    Dangerous capacitors exploding!? Are auto gasoline tanks safe??? Flammable gasoline is by far more dangerous than supercapacitors. Obviously commenters are oil company supporters and doing their best to propagandize against any technology threatening the oil dominance….

  3. John Marzich

    Their a fantastic “Electronic load Buffer” to minimize loads directly on batteries\circuitry. This adds a lot of extended life to the expensive batteries among other things.

  4. I used to work with high voltage high energy capacitors and the difference between batteries and caps is simply that a cap can discharge all the stored energy in microseconds while the battery will take minutes to only partially discharge . 200 watts discharged in a second by a battery is 200 watt seconds of energy…the same 200 watts delivered in a microsecond is 200 megawatts and that , baby , is a whole new ball game .

  5. I believe an awesome application for ulracapswould be to power electric dragsters. Think about it. Very high discharge rate for tremendous punch off the line, and since the race lasts only a few seconds, long run times and range are not an issue. Also the very short time it takes to charge these is very convenient at the track.

    • A capacitor to power such vehicle could blow up a vehicle like a big bomb, if there would be an accident and wires short out.
      You could charge such a capacitor quickly , but only if you haul a generator big enough to sit on a tractor trailer since it would need hundreds if not thousands of amps for an quick charge for a size of capacitor that would be needed for an dragster.
      Have you ever seen switch gears, breaker boxes or disconnects blown off the wall when they got shorted? I have seen it including a man that was catapulted backward 50 feet…. and capacitors and their devices would not be any different. Many people get killed every year from it from electrical blow ups.
      Search the internet

  6. Advanced electric vehicles will probably use a combination of storage technologies, including ultracapacitors and advanced batteries. Capacitors offer performance advantages for transient loads superior to batteries, but function poorly as long term storage devices. They also don’t like to be removed from a circuit without being discharged.

    The energy storage density solutions for both ultracapacitors and advanced batteries probably lie in the application of fractal geometry: the creation of devices with very high surface/volume ratios. This is a superficially obvious solution in the case of capacitors, derivable directly from the formulae for determining charge capacity. In the case of batteries, the advantage of fractal surfaces comes from greatly reduced internal resistance, resulting in improved efficiency through reduction in thermal losses.

  7. Paul Maher

    Whatever happened to Ampenergo? They licensed a technology from NASA some time ago that would allow them to make a housing out of graphene that would power the engine contained therein. They did this through the SBIR program. Oh my!! NASA has lots to share!! I understand that cathodes and anodes made of Graphene can do a lot for Lithium Ion batteries. Nearly as interesting as Graphene is Buckypaper.

    But when a Thermionic, Photovoltaic, Optical Rectification, Photoswitching, and LENR hybrid in a Graphene Hybrid environment happens things are going to move real fast. I believe that when we see Kurzweils rules apply to the energy industry you’ll get my drift.

    • Jack Henry

      Chemical batteries discharge rate at unpredictable rates depending on temperature, humidity, and how many times a battery has been charged. With each charge a chemical battery has to re-deposit some of the material that left the cathode during discharge. Not all of the material returns to the cathode so the battery is somewhat weaker with each discharge/charge cycle. A typical lithium ion battery can be cycled maybe 500 times before it becomes useless.
      Any capacitor (or supercapacitor) doesn’t work this way. During the charge cycle, electrons accumulate on one plate of the capacitor relative to the other. When an electrical path is made between the two plates, the energy stored in the cap with discharge at a rate determined by the current and internal resistance. This is not a linear function but it is easily managed with a constant current circuit.
      Capacitors can also be recharged indefinitely and are inherently much less expensive than chemical batteries. However the stumbling block in today’s supercapacitors is its own leakage current because the insulator between the elements of the two plates is not perfect.
      Energy density in capacitors is also not quite as good as a Lithium-Ion battery but this is not so important for electric cars since there is plenty of room for larger energy storage devices.

  8. Supercaps have been around for a couple of decades at least and are a much more elegant solution to energy storage than chemical batteries. They can be charged much faster than Lithium (or any other) batteries. They deliver more instantaneous power due to a lower internal resistance. They don’t use toxic materials. And can be recharged many more times than chemical batteries.
    Supercaps however have a relatively high internal discharge rate which means the charge that it holds will dissipate quickly and they have to be recharged often even if the power is not used.
    Energy density is currently somewhat lower than Lithium batteries but this will likely change with more development.

  9. A 1-Farad capacitor was once larger than a 10 foot cube. In 1990 a company introduced a 5 Farad capacitor the size of an American quarter dollar. Super capacitor research is moving at a rapid rate with surface expanding materials. Capacitors are superior to batteries in that there is no chemical activity involved, and a virtually unlimited lifetime. Batteries are inefficient in that electricity is converted to chemical energy (loosing 2/3rds of the energy in the process) and then reconverting the chemical energy back into electrical energy (loosing an additional 2/3rds of the energy). Capacitors don’t have these losses, just micro losses from heat dissipation while charging and discharging.

  10. winrob

    Per unit volume or by weight, gasoline has as much energy as nitroglycerine. Every electric storage technology is feeble by comparison. not to mention the lamentable difference in refueling time. Without the Fedgov ripping off the taxpayers with subsidies we wouldn’t even be reading this manure.

    • Commodore

      Grow up. Almost any technology can be abused to be a weapon. E.G., water, light as a laser, etc. keep in mind that energy unleashed in any form can be considered a weapon.

  11. For regenerative braking ultra-capacitors make a lot of sense. The weight is less than full batteries and they can be used to offset the costly accleration event fuel usage. Perfect for mild-hybrid applications.

  12. Phillip

    I want to buy hydrogen so oil companies can still take lots of money. Will they still be able to survive if these super-caps come on the market?

    I refuse to pay 10 bucks to drive 300 miles when I could pay 40..50, or even 60 dollars to drive the same distance using hydrogen.


  13. The only scary thing is what will happen if all that energy gets unleashed in an uncontrolled case (such as an accidents). Sure, batteries also can catch on fire, overheat, explode, but super capacitors can discharge all their energy much much more quickly…

      • Yes, I have seen this. When designing a power supply I saw the electrolytic capacitor blow apart due to a voltage surge. Dangerous chemicals and metal fragments were the result.

        • Many capacitors are made of exotic metals mined by exploited workers and causes terrible devastation of local environments. This is the real problem that needs to be sorted before an entire industry of greed converges on this evident solution – by then it’ll be too late.

        • Matt Carrell

          whatever… “dangerous fragments” from a popped cap would not leave the battery compartment. They would not fly into where the passengers are sitting.! As a tech who has seen many caps blow over the years (particularly electrolytic because they are polarized and denser), not one has ever “put my eye out” or caused injury. When they blow, I’ve never found any fragments of them anywhere. Sometimes they just quickly burn out. Sometimes a hole is popped through the top. Fragments? Not that I know of. Fire danger? If its in a metal box, I think not.

    • Up till now, super capacitors can only store a small fraction of the energy that a battery can store. That 4.4Volt, 350mF super cap in the iPhone picture, can only provide 100mA for 3.5 seconds before its voltage drops to 3.4 Volts. The battery right next to it can provide 100mA for more than 10 hours before it goes dead.

    • We had a large SuperCapacitor explode in the lab at a company I worked at in the past. It was for a US Army Hybrid truck. Yes, big explosion, but we knew that could happen, so the unit was surrounded by a thick Plexiglass curtain. Still, a lot of underwear had to be changed!

  14. Reblogged this on Carpet Bomberz Inc. and commented:
    Yes, supercapacitors might be the key to electronic vehicles that’s true. They are used now in different capacities as backup power for different electronic equipment and in some industrial uses as backup to distribution equipment. I think a company pursuing this should also consider the products and work done by American Superconductor in Massachussetts (NYSE: AMSC). Superconducting wire paired up with a electric motors wound with the same wire and a bank of Supercapacitors could potentially be a killer app of these combined technologies. Doesn’t matter what the power source is (Fuel Cell vs. plug-in), but the whole drive train could be electric and be high performance as well.