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Published on March 17th, 2009 | by Andrew Williams

22

New Capacitor Could Lead to Ultra-Efficient Electric Cars

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A team of US and Korean scientists have announced a major breakthrough in energy storage that could pave the way to a new generation of ultra-efficient electric cars, mobile phones and laptops.

The prototype capacitor, much more powerful than exisiting batteries, is capable of storing power at the same massive density as a supercapacitor (an incredible 10 billion tiny capacitors in every square centimetre), but releasing it as quickly as the fastest electrostatic capacitors.

Speaking about the invention, Gary Rubloff of the University of Maryland said, “Our primary target [for this technology] is as part of a hybrid battery-capacitor system for electric cars, but there are many [potential] small scale applications, [including] better electrical storage systems for cellphones or laptops.”

The microscopically small capacitors are created by anodising a layer of aluminium foil to make an evenly spaced array of nanopores across its surface. Three nested, concentric layers of material are then added to each pore, that function as in the same way as the conventional conductor-insulator-conductor set up of an electric capacitor. The interspersed conducting (titanium nitride) and insulating (aluminium oxide) layers are deposited using an ultra-precise process called atomic layer deposition.

As descibed in the journal Nature Nanotechnology, the resulting capacitor can hold 2,500 joules, and discharge one megawatt of energy, per kilogram.

The next stage for the team is to improve the device’s performance further by experimenting with deeper pores, capable of containing bigger capacitors and storing even more energy.

Image Credit – oskay via flickr.com on a Creative Commons license



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About the Author

is a writer and freelance journalist specialising in sustainability and green issues. He lives in Cardiff, Wales.



  • Mark

    “Could Lead To”, but won’t for many many years. It’s experimental.

  • Mark

    “Could Lead To”, but won’t for many many years. It’s experimental.

  • BenE

    2,500 joules per kilogram? That’s nearly nothing. EEstor claims nearly 1,000,000 joules per kilogram.

  • BenE

    2,500 joules per kilogram? That’s nearly nothing. EEstor claims nearly 1,000,000 joules per kilogram.

  • ChuckL

    BenE, There is a big difference between storage capacity and discharge rate. Please don’t use this difference as a straw man to denigrate this development.

  • ChuckL

    BenE, There is a big difference between storage capacity and discharge rate. Please don’t use this difference as a straw man to denigrate this development.

  • Anto

    BenE, Since EESTOR does not exist and never will, please do not use the claims of EESTOR specs for comparison…I am working with my partners Moe, Larry, and Curly Inc. developing a ceramic battery with a spec of 1,000,000,00,00 joules per kilogram, it will be ready for manufacturing in 3 to 5 years, forget EESTOR!

  • Anto

    BenE, Since EESTOR does not exist and never will, please do not use the claims of EESTOR specs for comparison…I am working with my partners Moe, Larry, and Curly Inc. developing a ceramic battery with a spec of 1,000,000,00,00 joules per kilogram, it will be ready for manufacturing in 3 to 5 years, forget EESTOR!

  • Miles

    Watt is a unit of power, not energy.

  • Miles

    Watt is a unit of power, not energy.

  • Allch Chcar

    I’ve seen a project with ultra capacitors. The 350volt bank took up the floor and knee space of the back seat and weighed over 100lbs. The only benefit was more off-the-line performance for his 400 kilowatt twin motored sports car.

    In reality they don’t provide any benefit to the range of an electric vehicle, just performance. Even low capacity batteries offer plenty of discharge capacity for continuous and peak power, it just takes a higher voltage pack.

  • Allch Chcar

    I’ve seen a project with ultra capacitors. The 350volt bank took up the floor and knee space of the back seat and weighed over 100lbs. The only benefit was more off-the-line performance for his 400 kilowatt twin motored sports car.

    In reality they don’t provide any benefit to the range of an electric vehicle, just performance. Even low capacity batteries offer plenty of discharge capacity for continuous and peak power, it just takes a higher voltage pack.

  • http://www.ladadadada.net/blog/2007/07/30/apocalypse_tomorrow David Keech

    A normal ICE car can produce around 25,000 joules per second. Electric cars typically use between 3 and 5 Watts when cruising but much more when accelerating. 100kg of this sort of battery would last for an hour on a flat track if the car didn’t have to accelerate at all and would last 10 seconds while accelerating. (The Tesla Roadster can produce up to 185kW so with only 25kJ available in the batteries, the Roadster couldn’t even accelerate at full throttle for a whole second.)

    I can’t help but think that the figure of 2500 joules per kilogram must be a typo. Considering the following sentence from the New Scientist article, mistakes and typos seem probable.

    “Now a prototype capacitor has been made that manages to store power as densely as a supercapacitor, but deliver it at speeds comparable with electrostatic capacitors.”

    For those who didn’t study physics at high school, power is not stored. Power is delivered. If it is stored, it is energy, not power. One would expect a journalist working for New Scientist to know this and to get it right.

    The original paper (or at least, the abstract) measures the capacitance in Farads which is normal for capacitance but not easily comparable to the figure of 2500J. It gives a value of 10 micro Farads per cm but rather than cm squared they have used cm to the power of -2. This notation seems confusing to me but I am going to assume that cm ^ -2 is the same as mm ^ -1 or m ^ -4 so if we multiply by 1000 throughout we get 10cm squared. Multiplying the rest of the values to get towards my guess at 1kg we get 10 Farads for a 10cm squared slice of 10 millimetere thick aluminium oxide. This is 100mL of the capacitor which, being aluminium oxide weighs about 250g. 1kg will be 4 times this and therefore will have 40 Farads which is quite a bit better than traditional capacitors which would struggle to get 1 Farad into this volume.

    Converting Farads into Joules requires knowing the Voltage that the system will run at… which I don’t. The voltage in electric cars varies between around 100 and 300 Volts. Using these two values, I get either 400kJ/kg or 3,600kJ/kg. Either way, it’s a long way from 2,500J/kg. 100kg of the 300 Volt sort would give us 360MJ or 100kWh. That’s 10 hours of driving at 10kW power usage. Average driving will use more than that but however you look at it, these are impressive figures.

    Please feel free to do the maths again to make sure I didn’t get it wrong myself.

    Dagnabbit ! I just spotted an error myself. I switched cm squared and squared cm right near the start. I think a quick division be 10 will correct the error but I can’t be sure without going through the whole lot again. This would leave us with 10kWh for 100kg of batteries which is still quite impressive.

  • http://www.ladadadada.net/blog/2007/07/30/apocalypse_tomorrow David Keech

    A normal ICE car can produce around 25,000 joules per second. Electric cars typically use between 3 and 5 Watts when cruising but much more when accelerating. 100kg of this sort of battery would last for an hour on a flat track if the car didn’t have to accelerate at all and would last 10 seconds while accelerating. (The Tesla Roadster can produce up to 185kW so with only 25kJ available in the batteries, the Roadster couldn’t even accelerate at full throttle for a whole second.)

    I can’t help but think that the figure of 2500 joules per kilogram must be a typo. Considering the following sentence from the New Scientist article, mistakes and typos seem probable.

    “Now a prototype capacitor has been made that manages to store power as densely as a supercapacitor, but deliver it at speeds comparable with electrostatic capacitors.”

    For those who didn’t study physics at high school, power is not stored. Power is delivered. If it is stored, it is energy, not power. One would expect a journalist working for New Scientist to know this and to get it right.

    The original paper (or at least, the abstract) measures the capacitance in Farads which is normal for capacitance but not easily comparable to the figure of 2500J. It gives a value of 10 micro Farads per cm but rather than cm squared they have used cm to the power of -2. This notation seems confusing to me but I am going to assume that cm ^ -2 is the same as mm ^ -1 or m ^ -4 so if we multiply by 1000 throughout we get 10cm squared. Multiplying the rest of the values to get towards my guess at 1kg we get 10 Farads for a 10cm squared slice of 10 millimetere thick aluminium oxide. This is 100mL of the capacitor which, being aluminium oxide weighs about 250g. 1kg will be 4 times this and therefore will have 40 Farads which is quite a bit better than traditional capacitors which would struggle to get 1 Farad into this volume.

    Converting Farads into Joules requires knowing the Voltage that the system will run at… which I don’t. The voltage in electric cars varies between around 100 and 300 Volts. Using these two values, I get either 400kJ/kg or 3,600kJ/kg. Either way, it’s a long way from 2,500J/kg. 100kg of the 300 Volt sort would give us 360MJ or 100kWh. That’s 10 hours of driving at 10kW power usage. Average driving will use more than that but however you look at it, these are impressive figures.

    Please feel free to do the maths again to make sure I didn’t get it wrong myself.

    Dagnabbit ! I just spotted an error myself. I switched cm squared and squared cm right near the start. I think a quick division be 10 will correct the error but I can’t be sure without going through the whole lot again. This would leave us with 10kWh for 100kg of batteries which is still quite impressive.

  • http://www.ladadadada.net/blog/2007/07/30/apocalypse_tomorrow David Keech

    By the way, there’s a nice picture of the nanopores in the supplementary material: http://www.nature.com/nnano/journal/vaop/ncurrent/suppinfo/nnano.2009.37_S1.html which you could use rather than some random picture of ordinary capacitors from Flickr, assuming the license or “fair use” allows it, of course.

  • http://www.ladadadada.net/blog/2007/07/30/apocalypse_tomorrow David Keech

    By the way, there’s a nice picture of the nanopores in the supplementary material: http://www.nature.com/nnano/journal/vaop/ncurrent/suppinfo/nnano.2009.37_S1.html which you could use rather than some random picture of ordinary capacitors from Flickr, assuming the license or “fair use” allows it, of course.

  • http://www.ladadadada.net/blog/2007/07/30/apocalypse_tomorrow David Keech

    Hmmm… replying for the third time in a row…

    Many people on the New Scientist website thought that 2500J seemed very low and someone did the same maths I did.

    The difference is that he assumed cm to the power of -2 meant cm squared. He also used 10 Volts and came up with 2500J. Volts are multiplied by twice in the conversion from Farads to Joules so multiplying up to 100 Volts changes the final value by an order of 10,000 which gives a value somewhere in between the two values I arrived at. He gets that for 1kg and I get it for 100kg but that can be explained by the cm squared difference.

    Another way of looking at it is that a AA battery holds about 10,000J and is a lot less than a kilogram.

  • http://www.ladadadada.net/blog/2007/07/30/apocalypse_tomorrow David Keech

    Hmmm… replying for the third time in a row…

    Many people on the New Scientist website thought that 2500J seemed very low and someone did the same maths I did.

    The difference is that he assumed cm to the power of -2 meant cm squared. He also used 10 Volts and came up with 2500J. Volts are multiplied by twice in the conversion from Farads to Joules so multiplying up to 100 Volts changes the final value by an order of 10,000 which gives a value somewhere in between the two values I arrived at. He gets that for 1kg and I get it for 100kg but that can be explained by the cm squared difference.

    Another way of looking at it is that a AA battery holds about 10,000J and is a lot less than a kilogram.

  • Brian Willoughby

    One thing a capacitor can do that a battery cannot, is integrate into the design formulas simply. Example, the impedance = 1 over 2 x pi x Freq x Capacitance. This also applies to the control/feedback formulas.

    Nanoparticles are interesting, as capacitance is directly proportional to surface area and inversely proportional to the distance between the plates.

    This may be why so many people are investigating this.

    I wonder what the operating range is. Most capacitors can go up to 105 C, but seem to have no practical lower limit.

    Lithium/NiMH go down to -30C NiCd =-40, but they can’t deliver a lot of current at that temp.

    Canadians are hoping the automotive industry goes with super capacitors, we tire of having to plug in our cars.

  • Brian Willoughby

    One thing a capacitor can do that a battery cannot, is integrate into the design formulas simply. Example, the impedance = 1 over 2 x pi x Freq x Capacitance. This also applies to the control/feedback formulas.

    Nanoparticles are interesting, as capacitance is directly proportional to surface area and inversely proportional to the distance between the plates.

    This may be why so many people are investigating this.

    I wonder what the operating range is. Most capacitors can go up to 105 C, but seem to have no practical lower limit.

    Lithium/NiMH go down to -30C NiCd =-40, but they can’t deliver a lot of current at that temp.

    Canadians are hoping the automotive industry goes with super capacitors, we tire of having to plug in our cars.

  • http://gas2.0 mark

    has any one thought about useing theese capacitors as a nitro tank in an ev? could give quite a boost!

  • Pingback: Tesla CEO Bets on Capacitors, Not Batteries, For Future of EV’s – Gas 2.0()

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