EEstor

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EEstor cell
EEstor cell

EEStor is a company based in Cedar Park, Texas, United States that claims to have developed a superior type of capacitor for electricity storage, which EEStor calls 'Electrical Energy Storage Units' (EESU). Its CEO and president is Richard Weir, who is also the inventor named on their principal technology patent.[1]

These units use barium titanate coated with aluminum oxide and glass to achieve a level of capacitance claimed to be much higher than what is currently available in the market. The claimed energy density is 1.0 MJ/kg (existing commercial supercapacitors typically have an energy density of around 0.01 MJ/kg, while lithium ion batteries have an energy density of around 0.54–0.72 MJ/kg).[2]

Based on these claims, a five-minute charge should give the capacitor sufficient energy to drive a small car 300 miles (480 km). However, standard household wiring is not capable of delivering the power required for this, so charging times this short would probably require purpose-built high capacity dispensing stations.[3] Overnight charging at home should still be practical[4], as is using a second EESU for the home which could be charged overnight using cheap, off-peak electricity to then charge the EEStor unit in the car in 5-10 minutes on demand.[5] Also according to Ian Clifford a normal household outlet with 110 volt supply can fully charge the EESTor powered CityZENN in 4 hours for a 250 mile range and a normal household outlet with 220 volt supply can fully charge the EESTor powered CityZENN in 2 hours for a 250 mile range. CityZENN target price is around $25000 - $30000. [6]


Contents

[edit] Technology

EEStor's technology, described in its patent, involves sintering very small grains of coated barium titanate powder into a bulk ceramic. The process is designed to eliminate the pore space left by sintering. Barium titanate crystals have an extremely high permittivity; however, voids allow current to arc through the dielectric (voltage breakdown), causing the capacitor to self-discharge. By eliminating the voids, the bulk ceramic has properties similar to that of individual barium titanate crystals. To keep costs down, the sintering occurs at low temperatures, enabling the manufacturer to use nickel electrodes instead of more expensive platinum electrodes.

The claims of the EESU are:

  • Nontoxic and non-hazardous
  • Non-explosive
  • For a 52 kWh unit, an initial production price of $3,200, falling to $2,100 with mass production is projected.[7] This is half the price per stored watt-hour as lead-acid batteries, and potentially cheap enough to use to store grid power at off-peak times for on-peak use, and to buffer the output from intermittent power sources such as wind farms.
  • No degradation from charge/discharge cycles
  • 4-6 minute charge time for a 336 pound (152 kg), 2005 cubic inch (33 L), 52 kilowatt hour (187 MJ), 31 farad, 3500 volt unit, assuming sufficient cooling of the cables.
  • A self-discharge rate of 0.1% per month

The capacitance in the patent is 31 Farads. To achieve such a high energy density the capacitor has a very high breakdown voltage and uses an operating voltage of 3,475 V. In the absence of dielectric saturation the formula for stored energy of a capacitor is

\mbox{E} = \dfrac{\mbox{C}\cdot\mbox{V}^2}{\mbox{2}}

which gives a total energy storage of 187 MJ or 52 KWHours.

[edit] Status

"Prototype components" have been produced in a laboratory setting with a relative permittivity of 18,500. In January, 2007, an independent company certified EEStor's production line's process as producing 99.9994% purity barium titanate powder, sufficient for achieving the desired permittivity.[8] Completion of development was to occur by the end of 2007. EEStor later offered a timeframe for delivery that was interpreted as a six month delay.[9] ZENN has denied that this is a delay, just a clarification of the schedule, separating "development" and "commercialization". ZENN further stated that the next milestone is permittivity testing, and there is no announced date for it at this point.[10]

On January 9, 2008, EEstor publicly announced that Morton L. Topfer, a former vice chair of Dell, was joining the board.[11]

In April 2008, ZENN Motors announced a highway speed vehicle for 2009 using EEstor's capacitors which will achieve 80 mph (130 km/h) speeds, 250 mile (400 km) range and charge in 5 minutes[12]

EEStor's US patent filed in 2001 mentions aluminum oxide and calcium magnesium aluminosilicate glass as coatings. The WIPO filed in 2005 mentions only aluminum oxide. Nickel was mentioned in the US patent as the electrode but it was changed to aluminum (1 micron thick) in the WIPO patent as a better and less expensive alternative. As stated in the patents, both changes were made possible by selecting the PET matrix (or coating) because it is pliable enough to fill voids at only 180 C.

[edit] Permittivity Questions

Critics have argued that EEStor's capacitor cannot store as much energy as claimed because the relative permittivity (aka "dielectric constant") stated in the EEStor patents could not be correct. EEStor reports a large permittivity at an unusually high 350 V/micron which is what allows the EEStor components to store more energy than any other capacitor. At such a large voltage per micron of dielectric thickness, the permittivity usually decreases due to a phenomenon called dielectric saturation. The world patent filed by EEStor in August 2005[13] contains permittivity data averaging 19,818 at 500 V/micron. No other researchers have reported such a high permittivity at such a high voltage/micron. The EEStor patents do not give an explanation for how this was achieved. This expected high permittivity at this unexpected high voltage/micron is the basis for EEStor to claim 10,000 J/cc in their modified barium titanate. The highest reported by others is on the order of 10 J/cc.

The EEStor patents cite a 1993 article [14] and a Philips Corporation year 2000 patent[15] as exact descriptions of its "calcined composition-modified barium titanate powder." In the Philips patent, this material is more precisely identified as "doped barium-calcium-zirconium-titanate". The Philips patent reports a permittivity of up to 33,500 at 1.8 V/micron. The Philips patent does not report the permittivity at a high voltage/micron, but it states it has "a low voltage-dependence." Replacing some of the barium with calcium broadens the optimum temperature range. Replacing some of the titanium with zirconium increases the permittivity. The other doping reduces the Curie temperature, Tc, that allows the peak of the permittivity to be at 85 degrees C. EEstor uses an aluminum oxide coating that the Philips patent does not.

An April 2005 patent[16] by the University of California shows that high-density barium titanate formed from sub-micron grains can double the maximum permittivity. It does not discuss the permittivity at high voltages.

An EEStor patent references a 2001 patent[17] that uses similar coatings on sub-micron particles of modified barium titanate. Under one set of conditions, they achieved a permittivity of only 2400 and did not report the permittivity at high voltages. Their breakdown voltage was 4 times less, a little over 100 V/micron.

Another source of concern for the reported permittivity is the 10 nm aluminum oxide coating which reduces the overall capacitance. A lower capacitance means a lower permittivity will be measured. Coatings act as capacitances in series which have a combined capacitance that is lower than the smallest capacitance in the series. EEStor states in the world patent that the coating reduced the permittivity by only 12%. They report a measured capacitance of 19,800*e*A/9.8 micron = 2,020*e*A, where "e" is the permittivity of free space and A is an arbitrary area of the electrodes. However, the permittivity for aluminum oxide is only 10 so that a 0.01 micron coating has a capacitance of 10*e*A/0.01 = 1000*e*A. The patent states the particles are 0.64 micron and the electrodes spaced 10 microns apart. This is about 15 layers of the particles between the electrodes, giving 30 layers (top and bottom) of the aluminum oxide coating in series with the barium titanate. So the total capacitance between the electrodes is a maximum of 1000*e*A/30 = 33*e*A which is 60 times less than what EEStor is reporting. This means the permittivity and storable energy would be 60 times lower than EEStor is reporting if the coating information in the patent is correct. Similar capacitance concerns can be stated for the PET (permittivity ~ 4 )which occupies about 5% of the volume according to the patent.

[edit] Partnerships

Equity funding for the company appears to come predominantly from Kleiner Perkins Caufield & Byers.

ZENN Motor Company (based in Toronto, Canada), which manufactures the ZENN, stated in April 2007 that it had invested $2.5 million in EEStor.[18]

On January 9th, 2008, Lockheed-Martin signed an agreement with EEStor for the exclusive rights to integrate and market EESU units in military and homeland security applications.[19] This was widely seen as lending a great deal of credibility to the company and its technology; ZENN, who had been taking flak for their investment in EEStor, saw their stock increase by 28%.[20] Lockheed has not yet tested prototypes, but did tour EEStor's facility and analyzed their technology and methodology. Lockheed was "very impressed" with EEStor, noting "they are taking an approach that lends itself to a very quick ramp-up in production." The two companies look to complete joint product testing over the course of 2008.[21]

[edit] Competitors

[edit] References

  1. ^ United States Patent 7,033,406. United States Patent Office (2006-04-25). Retrieved on 2007-11-24.
  2. ^ Hamilton, Tyler (2007-01-22). Battery Breakthrough?. Technology Review. Retrieved on 2007-11-24.
  3. ^ news.com - Hard-charging electric vehicles? - September 5, 2007
  4. ^ news.com - YOUR point: CNET News.com
  5. ^ economist.com - Ne plus ultra - January 31, 2008
  6. ^ zenncars.com - Ian Clifford discusses the ZENN, EESTor.. - June 02, 2008
  7. ^ The Energy Blog - EEStor Ultracapacitor Shuns Publicity - January 27, 2006
  8. ^ greencarcongress.com - EEStor Announces Two Key Production Milestones; 15 kWh EESU on Track for 2007 - 17 January, 2007
  9. ^ news.com - Is EEStor delaying its power system for cars? - September 4, 2007
  10. ^ Official Response from Zenn on delay of eestor (under Comment section written by afjerry on 09/11/2007 at 9:47 PM) (2007-09-11).
  11. ^ EEStor, Inc. is Pleased to Announce that Morton L. Topfer has Joined the EEStor, Inc. Board of Directors. Reuters. Retrieved on 2008-01-09.
  12. ^ Zenn outlines global ambitions for 80mph electric car (2008-05-04).
  13. ^ wipo.int - (WO/2006/026136) Utilization of Poly(ethyene Terephthalate) Plastic and...
  14. ^ S. A. Bruno, D. K. Swanson, and I. Burn, J. Am Ceram. Soc. 76, 1233 (1993)
  15. ^ Multilayer capacitor comprising barium-titanate doped with silver and rare earth metal - Patent 6078494
  16. ^ High-density barium titanate of high permittivity - Patent 6905649
  17. ^ Dispersible, metal oxide-coated, barium titanate materials - Patent 6268054
  18. ^ ZENN Motor Company Makes Equity Investment in Strategic Partner, EEStor, Inc.. Marketwire. Retrieved on 2007-09-10.
  19. ^ Lockheed Martin Signs Agreement with EESTOR, Inc., for Energy Storage Solutions. Pressmediawire. Retrieved on 2008-01-09.
  20. ^ ZENN stock leaps on Eestor's deal. The Toronto Star. Retrieved on 2008-01-10.
  21. ^ Lockheed Martin Signs Agreement with EEStor. GM-VOLT.com. Retrieved on 2008-01-10.
  22. ^ Nanowire battery can hold 10 times the charge of existing lithium-ion battery (HTML). Stanford News Service (2007-12-18).

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