New Nanocomposite Process Improves Barium Titanate Capacitors
27 April 2007
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| Scanning electron micrographs of barium titanate (BaTiO3) nanocomposites with polycarbonate (left, top and bottom) and Viton (right, top and bottom) polymer matrices. The images show the dramatic improvement in film uniformity. Click to enlarge. |
Researchers at Georgia Tech have developed a new technique for creating films of barium titanate (BaTiO3) nanoparticles in a polymer matrix that could allow fabrication of improved capacitors that are able to store twice as much energy as conventional devices.
Because of its high dielectric properties, barium titanate has long been used in capacitors, but until recently materials scientists had been unable to produce good dispersion of the material within a polymer matrix. By using tailored organic phosphonic acids to encapsulate and modify the surface of the nanoparticles, researchers at the Georgia Institute of Technology’s Center for Organic Photonics and Electronics were able to overcome the particle dispersion problem to create uniform nanocomposites.
Our team has developed nanocomposites that have a remarkable combination of high dielectric constant and high dielectric breakdown strength. For capacitors and related applications, the amount of energy you can store in a material is related to those two factors.
—Joseph W. Perry, a professor in the Georgia Tech School of Chemistry and Biochemistry and the Center for Organic Photonics and Electronics
The new nanocomposite materials have been tested at frequencies of up to one megahertz, and Perry says operation at even higher frequencies may be possible. Though the new materials could have commercial application without further improvement, their most important contribution may be in demonstrating the new encapsulation technique—which could have broad applications in other nanocomposite materials.
The key to developing thin-film capacitor materials with higher energy storage capacity is the ability to uniformly disperse nanoparticles in as high a density as possible throughout the polymer matrix. However, nanoparticles such as barium titanate tend to form aggregates that reduce the ability of the nanocomposite to resist electrical breakdown. Other research groups have tried to address the dispersal issue with a variety of surface coatings, but those coatings tended to come off during processing, or to create materials compatibility issues.
The Georgia Tech research team decided to address the issue by using organic phosphonic acids to encapsulate the particles. The tailored organic phosphonic acid ligands, designed and synthesized by a research group headed by Seth Marder—a professor in the Georgia Tech School of Chemistry and Biochemistry—provide a robust coating for the particles, which range in size from 30 to 120 nanometers in diameter.
Phosphonic acids bind very well to barium titanate and to other related metal oxides. The choice of that material and ligands were very effective in allowing us to take the tailored phosphonic acids, put them onto the barium titanate, and then with the correct solution processing, to incorporate them into polymer systems. This allowed us to provide good compatibility with the polymer hosts – and thus very good dispersion as evidenced by a three- to four-fold decrease in the average aggregate size.
—Joseph Perry
Though large crystals of barium titanate could also provide a high dielectric constant, they generally do not provide adequate resistance to breakdown, and their formation and growth can be complex and require high temperatures. Composites provide the necessary electrical properties, along with the advantages of solution-based processing techniques.
Though the new materials may already offer enough of an advantage to justify commercializing, Perry believes there are additional opportunities for boosting their performance. The research team also wants to scale up production to make larger samples—now produced in two-inch by three-inch films—available to other researchers who may wish to develop additional applications.
Perry and Marder are working with Bernard Kippelen, a professor in the Georgia Tech School of Electrical and Computer Engineering, on the use of these new nanocomposites in organic thin-film transistors in which solution-based techniques are used to fabricate inexpensive electronic components.
The results were reported in the April 2007 edition of the journal Advanced Materials. The research was supported by the Office of Naval Research and the National Science Foundation. Georgia Tech has filed a patent application on the nanoparticle encapsulation technique.
EEStor, the developer of a new high-power-density ceramic ultracapacitor (the Energy Storage Unit—EESU) for use in vehicles, is also working with barium titanate powders. The first commercial application of the EESU is intended to be used in electric vehicles under a technology agreement with ZENN Motors Company. (Earlier post.)
Resources:
“Phosphonic Acid-Modified Barium Titanate Polymer Nanocomposites with High Permittivity and Dielectric Strength”; P. Kim, S. C. Jones, P. J. Hotchkiss, J. N. Haddock, B. Kippelen, S. R. Marder, J. W. Perry; Advanced Materials Volume 19, Issue 7 , Pages 1001 - 1005
This smacks of copying EEstor, I'm glad you posted that bit at the bottom. Their patent is for a Barium Titanate Capacitor, and their first, and only new release was about certifying their purifying process for their materials.
The big detractors of EEstor say that the K value EEstor claims is impossible, but here we get the same basic claims from a respected university.
This lifts my skeptic lid a tiny amount. I still won't believe it till something is running, but this would be a fantastic breakthrough.
Posted by: Greg woulf | 27 April 2007 at 08:28 AM
So...big question, how expensive would BaTiO3 ultracapicitors suitable for PHEV and BEV's be? Are we talking cheaper than Li batteries? Would they have longer service lives under harder conditions? Could they be used as the first 30% of the electrical storage to reduce the number of discharge cycles for the batteries and extend the service life of the combined system?
Posted by: C Harget | 27 April 2007 at 08:35 AM
2X the performance of normal Ultracapacitors, not bad; EEStor claims 50X but then again EEStor is likely a scam.
Posted by: Ben | 27 April 2007 at 08:52 AM
If you can get an ultracap that can absorb the energy of a 2 ton vehicle decelerating from 40 - 0 mph, we will have something - you could build a decent HEV with a small(ish) battery that would work well in cities.
It won't give you the 20 - 40 mile range many people consider essential, but it would give you a very good town car.
Posted by: mahonj | 27 April 2007 at 09:02 AM
@ C Harget -
ultracpacitors are not drop-in replacements for batteries. The two are more like sprinter vs. endurance runner. UCs store energy electrostatically, so there are no chemical reactions on the surfaces of the electrodes in normal operation. That means they can be deep-cycled hundreds of thousands to millions of times with little degradation in performance.
UCs can be charged and discharged very quickly, so they are ideal for high-power applications such as recuperative braking of a vehicle. What gives them such high capacitance is the enormous surface area created by voids and pores. The electrolyte is typically an organic salt in solution.
Unlike batteries, whose terminal voltage changes little with state of charge until they are almost empty, UC voltage is proportional to the square root of the state of charge. This has obvious implications for the power electronics layout. Additional measures are needed to optimize capacity in series and parallel chains of UCs, all of which makes UC solutions relatively bulky and expensive based on high-cycle kWh capacity (not so on high-cycle rated power!)
In a nutshell, UC hybrids permit a substantially downsized ICE to be operated at high torque load most of the time. This saves a lot of fuel by reducing losses due to internal friction, especially in stop-and-go traffic, but that ICE does have to run almost all of the time.
One reason UCs have not made significant inroads in hybrid electric vehicles is that California's ZEV legislation is specifically designed to minimize regulated emissions by maximizing credits for vehicles with high all-electric range. The schedule does call for reduced credits by 2009.
Only recently has CO2 a.k.a. fuel economy entered into CARB's thinking - which 11 other states have now signed up to. After losing a case before the Supreme Court, the White House/EPA are now dragging their feet on giving CARB the waiver needed for CO2 regulation. Once that is awarded, CARB may decide to revisit ZEV wrt UC-based concepts.
Recommended reading on UCs:
http://ecass-forum.org/eng/
http://www.maxwell.com/
http://peswiki.com/index.php/Directory:EEStor
Posted by: Rafael Seidl | 27 April 2007 at 09:03 AM
C Harget,
In theory BaTiO3 caps would be cheaper then LiIon batteries simply because of the lack of complex membranes, over-charge and undercharge circuit protection, etc, then again caps will need circuits to stabilize their voltage as they discharge. Because caps are completely solid state (batteries have moving ions) they are know for lasting through millions of recharge cycles, only spontaneous shorting burning holes through the insulators is a major cause of wear and this only happens if overcharged.
Posted by: Ben | 27 April 2007 at 09:09 AM
More should be known about the ESStor 15-Kwh unit by end of 2007 when they are delivered to Feel Good Cars (Zenn)
A combination (ultra-caps + advanced Li batteries) may work for the life of a vehicle if appropriate control systems + cost + weight + size can be addressed successfully.
Future quick charge, long life, advanced batteries may preclude the use of ultra-caps, except for heavier vehicles such as city buses, delivery trucks etc where the energy boost from ultra-caps would be an asset to get moving from hundreds/thousands daily stops.
Posted by: Harvey D. | 27 April 2007 at 09:17 AM
Ummm...only CERAMIC capacitors hold true to what is described here.
Electrolytic capacitors are KNOWN to fail in a much smaller time frame if subjected to environmental extremes.
Posted by: Patrick | 27 April 2007 at 09:17 AM
The process discussed is for materials built on thin film (i.e. low voltage) polymer-based matrices indicating for now the application to thin-film components like capacitors and semi-conductor junctions. The next question is can this coating process assist ceramic U capacitors such as EESTore? Organic semi-conductors have been around for a while now demonstrated by the OLED applications in consumer electronics.
Posted by: gr | 27 April 2007 at 02:48 PM
I have a correction to rafael's post.
Voltage of a capacitor is directly proportional to the charge, q=vc. Energy is proportional the the square of the voltage, E=1/2 *cv**2. Further, for a fixed geometry, capacitance is proportional to the permittivity constant and the working voltage of a capacitor is proportional to the dielectric strength. BaTiO3 has high values for both so BaTiO3 capacitors may be great energy storage devices for electric vehicles.
Posted by: glenn | 27 April 2007 at 07:39 PM
@ Glenn -
you're right, I got the two mixed up. My apologies.
Posted by: Rafael Seidl | 28 April 2007 at 08:12 AM
As I understood EEstor's rebuttal to the critics dismissal of the unobtainable K-value, their "capacitor" design is actually a hybrid including some design elements from lithium-ion batteries, so may store electricity both electrostatically and chemically.
If this is true, maybe it's still possible that they have developed a device capable of their claimed power, cycle and energy density goals?
Posted by: clett | 28 April 2007 at 09:56 AM
As for EEstor ... all we have to do is wait ... Fingers crossed.
Posted by: Neil | 28 April 2007 at 07:07 PM
How long do we have to wait for EEstor to demonstrate it's prototype in public? By the way they should have produced a prototype long before they started building a factor.
Posted by: ben | 29 April 2007 at 10:57 AM
The EEstor is supposed to be in the ZENN later this year. I would assume that Feel Good Cars (if they have any brains) already has a prototype in their hands to work with. No law says they have to show it to anybody. People that are suspicious will figure that FGCs is in on a scam.
Posted by: Neil | 29 April 2007 at 04:35 PM
could someone please tell me why eestor would continue a scam like this for so long,mr.weir recently again stated they will present all they have been promising.he holds patents from ibm days he is no prankster for sure,kleiner,perkins would surely have to had seen a working model before forking over 10 million .could it not be possible they have somthing very special here,anytime a great invention comes along its greeted with this kind of ...........,,,,,,,
Posted by: johhny | 29 April 2007 at 06:30 PM
EEstor makes some very impressive claims and shows no proof, now look they may not be a scam, but until their claims are proven its best to be skeptical. Cold fusion anyone?, EEstor is basically on the same level: their patent says nothing of how to overcome many huge problems with BaTiO3 capacitors or so critics claim (which might explain their secrecy in another way in that they might not have yet patented the secret that makes their capacitors work) now there no law they have the show their product works publicly, but there no law I have to believe them if they don't. Until then I guess I'll have to wait until FGC comes out with a ESU powered car that gets the range and power claimed before I'll believe EEstor is for real.
Posted by: Ben | 30 April 2007 at 08:37 AM
Not to be argumentative, but EESTOR is painfully quiet. They've held one press conference that I've ever heard of and that was to announce that they had certified a purifying process. Their web site is just a holding page.
I'm not saying they're going to hit their patent numbers, but I doubt they're scammers. This report from Ga. Tech just caught my eye because it sounds remarkably similar to EESTOR. If even a bit of what EESTOR claims is true, then why wouldn't more be true.
Posted by: Greg woulf | 01 May 2007 at 07:33 AM
I become amazed sometimes on what they issue patents for. In the early days of U.S. patents, you used to have to bring in a working prototype. They did away with that and now you can patent lots of things that may not even work...ever. They just have to be of use and not violate any laws of physics. Does not seem like a good system to me.
Posted by: SJC | 04 May 2007 at 09:20 AM
I dont see this thing as anything fundamentally breakthru as I have been working on this thing myself and I can confirm that if you google "high dielectric constant polymer ceramic" (or breakingdowns of this phrase) you will find many scientific papers on this phenomena. Similar research on different materials have been investigated by many other groups in the past years.
Their inspiration for this research may be as follow:
BaTiO3 is very high dielectric constant material but not highest in terms of dielectric strength
Coat it with some material with better dielectric strength
mix in polymer for better coating/pasting ability on different electrodes
It is something like material A has very good property a
B has good property b
C has good property c
combine A, B, C and expect to have good properties a,b,c of the composite.
But in most of the cases, you cannot get the best of all properties a, b, c.
So G.A tech group is very reserved in claiming their finding as most scientists and engineers do. They do not say anything about "product" yet. i believe their capacitor will work for few volts potential, not thoudsands of V as for the case of EEstor
For the case of EEstor, they need to show more evidences to support their case at patent office.
their material consists of 3 layers, 1 BaTiO3 (dielectric constant 33,000) and 2 coating layers (dielectric constant 10). If somebody studies Electrodynamic will know that the equivalent dielectric constant will drop far lower than what they claim. if some special effect happen here they need to show it by experimental evidences to the patent office. I am amazed how they got the claim patented.
not counting the fact that dielectric constant is not really a constant when you apply very large voltage at the capacitor electrodes.
Posted by: qh234 | 16 June 2007 at 05:21 AM