I've been watching nanoparticles ultra-capacitors.  Generically, the concept has potential.  The Achilles heel is mechanical failure of the dielectric.  One small short and the device fails permanently.  

I have also been watching Greentech.  Many, if not most, of the technologies have been spun to the moon.  Investors beware.

 I'm amazed at how the recent spate of articles about EESTor (this being one of them, although it is entirely derivative and adds zippo to the state of our knowledge) acts as though this company suddenly appeared from the bowels of an alien spacecraft.  They've been around for 11 years, with at least some participants migrating from auto industry veteran supplier TRW up north. The biggest hurdle they face in terms of credibility has been the fact that their claims so completely exceed the current state of capacitor capabilities. They also claim benign failure characteristics never before seen with capacitors. The article also neglect to mention problems other than energy capacity : capacitors have a high leakage rate that makes their use
problematic for applications such as autos. Also not mentioned are their  undesirable failure characteristics.
   EESTor is THE big unknown when it comes to handicapping future electrical storage  technology. Let's all pray they succeed. They have claimed commercial production within 10 months and will deliver a test battery pack to ZENN before then. The article claims before year's end, but that is no longer valid - it should occur, obviously, before production begins, most likely early next year. ZENN stock has been volatile, and mostly volatile upwards the past several weeks since new talk of EESTor has emerged. ZENN has made no mention of a bona fide, highway capable electric car, probably because they can't build one - all their current products are low speed, neighborhood death traps that don't meet any Federal safety standards.

UltraCapacitors are not as fantastic (in the sense of difficult to believe) as they sound.  A lot of people are working on them, and I don't think there is any doubt that if we retain a technical civilization for long enough, we will have them some day. On the other hand I am very skeptical that EESTOR will be the ones to deliver them. First of all they have already missed a deadline. They originally claimed they would have them by August. Yes they have serious money behind them; but the serious money is super-high risk capital - people who make money by losing their investments 8 of 10 times, and make up for it by getting twenty-fold returns the other two.

EESTOR has kept the details of their tech confidential so far. They filed a patent that really does not disclose how their system works: you could not build an EESTOR from that patent.

My guess: they made some sort of genuine breakthrough in the field, but were overenthusiastic in thinking that their breakthrough was so key, that clearing the remaining obstacles would be routine. Their sincerity, enthusiasm and real technical achievement convinced both themselves and investors; but the breakthrough turned out not to be enough to get them to a commercial product, or (unless there is news I have not heard) even to a working prototype. So it does not come across as a scam, because it was not intended as a scam; it was the overoptimism inventors and entrepreneurs are often guilty of.

I hope I'm wrong and in turns out to be real. But I doubted it a year ago, and doubt it even more now.

"...thereby being inherently inefficient"

So you're lugging a bit of extra weight around. But the efficiency of EVs completely outstrips fossil fuel and will be superior to hydrogen vehicles. To call them inefficient on the basis that their weight doesn't change is completely wrong.

Unless batteries in electric cars are very different from any other kind of battery, they share with capacitors the "added bonus" of having no moving parts.

Unless you were comparing them to the internal combustion engine, in which case that is definitely not made clear in the sentence.