> it may one day
How long after oil peak, ie. the end of cheap and abundant oil?
> Electric cars have a lot of advantages. They don’t directly use fossil fuels
Indeed. Indirectly, withouth oil, we can't build cars, electric or otherwise: No oil, no mining industry, no plastic.
> they have zero emissions
Locally, but certainly not on a national level, since the US, along with China and Germany, use a lot of coal-powered electric plants. Go nuclear.
> Lithium-ion batteries have a lot of energy, but are limited in how fast they can discharge it
They're also way too expensive. Even if Tesla can come up with a $40,000 EV in the next few years, that's still way too expensive for a lot of people.
But still, combining a supercap and li-ion batteries is worth trying.

"...and not rare earths like lithium,..."
"Rare earth" refers to a specific set of 17 elements. Lithium is not one.

It says "...the supercapacitors can store enough energy to charge the battery..."
Then what's the point of having the battery?

So what happens when you get in an accident and the electricity is discharged through your body?

One of the main reasons to add supercapacitors is that they can handle hundreds of thousands or millions of charge-discharge cycles, which saves the battery from wearing out in acceleration / regenerative braking cycles.
It requires a great deal of supercaps, though. It takes over 0.2kWh to get a 4464lb car (Tesla S, 60kWh battery) to 60mph, and you can't use all the theoretical energy in the capacitors because running at too high a voltage shortens service life and the capacitors can't be drained fully while maintaining power. Putting them in body panels may help with cooling, which is the other thing needed for long capacitor life. (Dark cars parked in the sun may be bad for the capacitors, though.)
So if you can use 70% of the stored energy and the capacitor maximum voltage is a typical 2.5V, you need nearly 1/3 of a million farads of capacitor to buffer all that energy. With the most popular manufacturer's "Ultracapacitors", that 0.29kWh total energy is still less than 50 kilos (110lb) and 37 liters of space ( = 1/3 m = 13 inch cube).
Even with 4 m^2 (43 sq ft.) of body panel capacitors, they'd still be about 1 cm thick. If they really are structural and not brittle, then these could be very strong and damage-resistant, but if the panels did get damaged, they would undoubtedly be very expensive to replace.

Finally a good idea instead of all the co2 spewing hot rods. Check out this "New" material that is making the manufacturing of super capacitors much cheaper than using graphene: http://www.gizmag.com/hemp-high-performance-supercapacitor/33435/

piperTom, read the article again. The super capacitors and the batteries serve two separate purposes based upon their diverse operating characteristics. The article explains this quite clearly.

@Freyr Gunnar Nuclear Going nuclear while having the option of safer, cleaner and cheaper wind and solar power is not really clever. Have you read my reply to your comment here? http://www.gizmag.com/solar-powered-pathway-netherlands/34613/
Price of electric cars Yes the price is still pretty steep. But its already partially compensated by lower operating costs (lower maintenance and fuel costs). There are already electric cars selling for under 30 000 $ (http://en.wikipedia.org/wiki/Renault_Zoe) so no need to wait for a 40 000 $ Tesla. From an engineering standpoint electric cars are simpler compared to ones based on combustion engines. It can be expected that mass production will drive the costs for electric cars much lower in future. This also becomes obvious if you look at the cost development of batteries (main cost factor for electric vehicles) for the last few years and decades: they are falling. (http://cleantechnica.com/2013/07/08/40-drop-in-ev-battery-prices-from-2010-to-2012/)
@piperTom Yes that does not really make sense as it is written in the article. EH correctly explained the advantage of having supercapacitors in electric cars.
@Noel K Frothingham Well I think EH explained it much more clearly. Charging the capacitors to charge the batteries does not seem to make any sense. Electric cars already accelerate much better and sufficient compared to non-electric ones. Faster charging times only become a benefit if you also can store enough energy in the capacitors to drive without batteries for longer durations. If it is just enough to accelerate the car to 60 mph as EH calculated you will still need to charge the batteries giving you no charging time advantage.

I bet the insurance premium would not come cheap. It takes just one dent.

As this technology develops it certainly has the potential to eventually displace the li-ion and be the only energy storage. What I find cool about it is that it places the battery with something that is external to the car. All over it. If these are thin and can be laminated on top of each other then the total energy capacity can be determined by the thickness of the body panel. There is a whole lot of surface area on a car's skin to be used for this.
I absolutely love this brilliant and possibly revolutionary idea.