EESTOR patent issued

[Dr Mordrid]

On December 16th the Texan tech company EEStor was granted a US patent for their Electrical Energy Storage Units (EESU's). An EU patent is pending.

In essence the EESU is a highly controversial ultracapacitor which many feel is too good to be true, but if it is true it's a revolution in energy storage that in one stroke would pretty much make obsolete every battery tech now in use.

The question of course is if this is vaporware or real.

Patent here....(PDF)

Have at it guys

Because of this potential defense/space giant Lockheed Martin signed a license with EEStor last year for use of EESU's in military and Homeland Security applications. ZENN of Canada owns the EESU license for small and mid-sized 4-wheeled vehicles and LightEV has the two and three wheeled license.

The core ingredient is an aluminum coated barium titanate powder immersed in a polyethylene terephthalate plastic matrix. The EESU is composed of 31,353 of these components arranged in parallel.

They claim a total capacitance of 30.693 Farads and that this unit can hold 52.22 kWh while weighing just 281.56 pounds, including the box and all hardware.

Unlike LiION's EESU's are claimed not to degrade with cycling. EEStor also claims that EESU's cannot explode when being charged or if impacted, making them safe for vehicles.

[Mehen]

That table on page 7 definitely makes it look to good to be true, but if they can get close to that it would be amazing. /me crosses fingers!

[Marshmallowman]

If you look it as a capacitor some of the values make more sense than comparing them to batteries.

The amazing part all comes in the charge density and capictance they say they have achieved.

Though charging something like this in 3 minutes does make wonder about interconnects melting or even exploding with the amount of current they suggest it can absorb.

If eestor does what they say then eletric cars are here... maybe even electric hover cars

[Brian Ellis]

As I see it, the biggest hope for these is not for main energy storage but for supplying surge currents. If you take Li-ion, a surge current (e.g., good acceleration in a car) knocks hell out of the battery, causing overheating of the weakest cells which then overheat again during the charge. To some extent, this can be minimised, but not eliminated, by the cell design, but at the cost of a lower capacity. A compromise is therefore required, between capacity, weight and longevity and this compromise has not yet been resolved.

If the battery keeps a capacitor charged, the surge currents can be supplied by the capacitor, while the battery remains cool, gently replacing the charge into the capacitor at a much lower current than the surge current, therefore keeping it cool and extending the battery life.

However, there are many disadvantages of such a system. Firstly, the capacitors operate at a very low voltage, compared to the battery. This means that expensive 2- or 3- stage voltage converters are needed for both the charge and discharge circuits, The charge converter would be high-efficiency, say 85-90%, but the first stage of an up-converter would be unlikely to be better than 75% because the threshold voltage of the semiconductors is significant, compared to the capacitor voltage. This would imply that silicon (typically 0.7 V at 20°C) could not be used, but a much more expensive alloy and that thermal dissipation would need to be seriously addressed. Such converters would be very heavy, bulky and expensive. As has been mentioned, wiring in the kiloampere range is not child's play, either. It would have to be done with cast copper bars, say, 75x35 mm section and these would be neither cheap nor weightless. However, the biggest problem is whether the energy stored in a capacitor is even readily accessible. A battery has a relatively constant voltage over its discharge cycle. A capacitor has an exponential discharge curve, meaning that the voltage drops very rapidly at first and then the drop slows down, asymptotic to zero. This is not what is needed for sole energy storage, but is OK for surge currents, provided the up-converter can be made to work with a wide range of input voltages without losing too much efficiency. The whole notion of using a capacitor as the sole means to drive a car is almost ludicrous.

If you want to see what I mean in practice, buy a dozen 500 µF 5 V electrolytic capacitors, wire them in parallel and charge them to 5 V. Then discharge them into a small electric motor with a load, such as fan blades. You will get an initial blast of air which will rapidly die down to a gentle breeze until the motor stalls.

[Marshmallowman]

That may not be such a bad thing, from start your cap is fully charged and you use it to accelerate to full speed.
So the high initial discharge is good for initial accelerating, current requirement while cruising is not so high.
If you leave you cap discharged while cruising and only charge it when braking, since your cap is empty it will just eat up the power dumped in when you start braking.

But your other points are good.

[the main lobe]

This is really cool stuff... If this is all as simple as it seems, a little number crunching reveals that this relatively light weight 30.693F capacitor can be charged to 3500 volts. (U = 0.5*CV^2)

And this also seems to imply that they have created a capacitor that weighs just over 4 grams, has a capacitance of 978uF, and can handle 3500 volts.

[Brian Ellis]

Mea culpa, I assumed this was a supercapacitor. My remarks regarding low voltages do not apply. Instead, I would guess the best application for this device, if charged to 3500 V, would be an electric chair! However, my other remarks are still valid. Insulation would be more of a problem than copper at these voltages. However, the biggest problem, as I see it, would be that car mechanics would not be happy (they are already unhappy working on the ~200 V systems of hybrids! ). There would be no great technical problems to have DC>DC converters 200<>3500 V using silicon technology and efficience of >90% in each direction would be achievable.

Big question: will it work reliably with the figures quoted. Frankly, I have my doubts. BaTiO3 is a ferroelectric dielectric. This means that it has piezoelectric characteristics, whereby a mechanical stress will induce a strain that will generate a high voltage. Conversely, applying a high voltage will mechanically alter its dimensions. The former can be seen in the spark gas lighters on the market. You push a button and this flicks a BaTiO3 crystal which generates sufficient volts to provide a spark. The opposite effect is used for, e.g., some ultrasonic transducers. I speculate now: I don't think that these are conventional capacitors because there is no way any ceramic like BaTiO3 will have a dielectric constant exceeding a few hundred. I think that what may be happening is that when you apply a voltage, each particle of powder changes shape but is restrained by the PET matrix and this stress is relaxed by the discharge. This would give a characteristic similar to a capacitor but will not work like one with an accumulation of electrons on one side of the dielectric boundary. IOW, it is electromechanical, rather than electronic. If this is so, then there could be mechanical fatigue in the matrix with repeated cycles. This could be exacerbated if the thermal bond between the PET and the powder fails through stress cracking (common with many polymers); if this happened, it would be possible that punch-through may occur.

Another question that could arise: can they be mass-produced with the same characteristics? I suspect that there is a single prototype, at the most, that has been made, probably with hand-selected elements and probably scaled down from the figures quoted.

What puzzles me is that the patent spec is far too specific. I see BaTiO3 mentioned but there are other ferroelectrics which may work even better, such as lead titanate, lithium tantalate or lithium niobate. If I were patenting such a system, I would make sure the spec covered all potential materials. I'm darn sure that I could copy the idea using other materials without infringement.

[Dr Mordrid]

IIRC there is a previous EEStor patent circa 2005-ish that may be more specific regarding materials. I'll have a look.

I know for a fact that a lot of their lab work has been verified by the Southweset Research Institute (SwRI) in San Antonio, one of the best non-profit research labs in the US (though in fact they're international).

One of SwRI's more recent projects is the New Horizons probe which is on its way to Pluto.