Published on May 11th, 2011 | by Nicholas Brown


Cheaper Ultracapacitors for Electric Vehicles

May 11th, 2011 by  

Nanotune, a company from Mountainview, California recently reported that they developed ultracapacitors with energy storage capacity comparable to that of lead-acid batteries (35 Wh/kg). Wh = Watt-hour.

Conventional ultracapacitors, otherwise known as supercapacitors or ELDC (Electric Double Layer Capacitors), charge in seconds, do not require replacement when used as batteries, and are able to provide large surges of power in short periods of time without overheating. Their disadvantages include an extremely high capital cost, and a very low energy to weight ratio of 5 Wh/kg (which basically means that ultracapacitors are heavy).

To clarify the important difference between cost and price tag of batteries: The long term cost of batteries is not equal to the price tag. The cost of the batteries over a 20-year period for example is 2 x the price tag of the batteries if the batteries last 10 years. Supercapacitors last significantly longer than batteries. So, even though these supercapacitors initially cost $2,400 to $6,000 per kWh of energy storage, and the lithium ion batteries used for electric vehicles initially cost $500 to $1,000 per kWh, in the long term, supercapacitors may be cheaper or comparable.

The cost of the supercapacitors after 40 years is $2,400 to $6,000 per kWh if they last that long, and the batteries are actually $2,000 to $4,000 after 40 years if they last an average of 10 years, because they would have to be replaced at least 4 times for every one time that the supercapacitors are replaced. Of course, the supercapacitors would only be cheaper than the batteries if their initial cost is less than $4,000, since that is the maximum cost of the batteries. Nanotune claims that the initial cost of its supercapacitors could decrease to $150 per kWh provided that certain material costs, including the electrolyte, continue to decline.

Charge Time is Another Important Cost Factor

Batteries take hours to charge. Therefore, if you run out of power before you reach your destination, then you will have to plug in for 3 hours or more depending on the battery and charger used. (It can be less than an hour, though, and charge time is improving.)

This causes range anxiety, which is a major purchase deterrent for electric vehicles, and it puts a tremendous amount of pressure on manufacturers to maximize range, and this usually involves very large battery packs. Very large battery packs are very expensive.

Due to the fact that supercapacitors charge in seconds, fewer of them can be used, and the consequence of that is a shorter range than a battery-powered vehicle, but that is feasible since it is easy and convenient to charge these supercapacitors.

Nanotune is making supercapacitors with electrodes that have pores spaced 4 to 5 nanometres apart, but they say that they can make them smaller, which would improves surface. Improving surface area also improves storage capacity. So, this could go a ways towards making supercapacitors more practical and competitive.

h/t Technology Review

Related Stories:

  1. The Battery That Keeps on Going?
  2. Machine Invents New Li-ion Battery

Photo via Tennen-Gas

Check out our new 93-page EV report, based on over 2,000 surveys collected from EV drivers in 49 of 50 US states, 26 European countries, and 9 Canadian provinces.

Tags: , , , , , ,

About the Author

writes on CleanTechnica, Gas2, Kleef&Co, and Green Building Elements. He has a keen interest in physics-intensive topics such as electricity generation, refrigeration and air conditioning technology, energy storage, and geography. His website is:

  • Bob_Wallace

    “We’re trying to develop….”

  • Conspiracy_Fax

    Look, they are not going to give us the technology that will make combustion engines non competitive.

    It is called “disruptive technologies” and are routinely suppressed by governments as “national security” even as we face apocalyptic disaster in Japan any moment.

    (yes- look it up, Fukushima is more dangerous than ever an has the chance of a complete 6 reactor melt down during an upcoming operation to decommission reactor 4. There are 6,000 spent fuel rods that could fission for centuries and make the northern hemisphere uninhabitable.

  • Anonymous

    BYD recently released the results from their first year of real-world EV tests.  A fleet of e6 EV worked the streets of Shenzhen as taxis.  The fleet averaged 36,400 miles, a bit more than 3x  the average distance driven by US drivers and were mostly ‘rapidly recharged’ without damage to the lithium-iron-phosphate batteries. 

    Rapid recharging can be done in less than 30 minutes (possibly in less than ten minuted) and will give the batteries an 80% charge.  (The last 20% needs to be charged at a slower rate.)

    If BYD’s batteries survived “three years” of rapid recharging without any noticeable decrease in performance then the standard against which ultracapacitors has been raised.

    • zach vogel

      when he says seconds, he means seconds to full capacity 30 min is still a lot of time when you think about being on a road trip.

      • Anonymous

        If you’ve got at least a 200 mile range you won’t need to charge that last 20%. The Leaf can charge 80% in less than 20 minutes with a new charger apparently on the way which will cut the time to below 10 minutes.

        A 500 mile driving day would take two short stops. Driving a gas powered car 500 miles will require at least one stop to refuel. And most people are going to want to stop more than once in a 8-10 hour driving day.

        Ultracapacitors are capable of much faster charging and are capable of thousands of charge/recharge cycles without damage. But size, so far, kills. They just can’t store enough electricity in a small enough package to work for EVs. It’s going to be a race to see whether ultracapacitors or batteries win. At this point batteries are in the lead.

  • sola

    These capacitors will usually be put into hybrids and EVs in order to improve the braking regeneration ratio (which is quite low since even the best NiMh batteries cannot tolerate those brutal deceleration amps).

    In the case of EVs, they will be used as a temporary buffer, not the main battery, since its energy density is still way to low (at 35wh/kg).

    As far as I know, It is common practice in todays hybrid buses to use large ultracapacitor banks for the above reasons.

  • For me, the biggest thing with thinking about buying an electric car is range anxiety. I drive about 50 miles round trip each day for work. None of it is highway, about 15 of those miles are stop and go between traffic lights or lines of cars at stop signs. A scenario that I just know isn’t conducive to energy efficient driving. So, cheaper, lighter power storage to increase range is certainly something I’m keeping my eye on.

  • BillW

    This is great news! One catch with being able to charge in seconds, though, it that it requires a charging system that can deliver that much current. This will require power storage at charging stations.

    • flamefront

      Good point – for that even more capacitors are needed. But not twice, just a small fraction because those would have to be charged from the grid.

Back to Top ↑