EEStor is a company based in Cedar Park, Texas, United States that claims to have developed capacitor for electricity storage, which EEStor calls the 'Electrical Energy Storage Unit' (EESU). The claims are described in detail in two of the company's patents, US 7033406  and US 7466536 . EEStor claims that its capacitor can store more energy than lithium-ion batteries used in portable devices for cheaper than the low-cost lead-acid batteries used in gasoline powered cars. Its claims, if true, would radically change the electric car industry. However, the company has repeatedly missed research deadlines and still has not publicly demonstrated the technology. Despite this, EEStor's partner, Zenn motors, raised CAD$2 million from investors primarily on the promise of EEstor's technology.
Claimed specifications 
|Volume (litres/cubic inches)||74.5/4541||293/17,881||705/43,045||93.5/5697|
|Self-discharge rate||0.02%/30 Days||5%/30 Days||1%/30 Days||1%/30 Days|
|EV Charging time (full) - 100% charge||3-6 min||>3.0 hr||3-15 hr||>3.0 hr|
|Life Reduced with deep cycle use||none||very high||high||very high|
|Temperature vs. effect on energy storage||negligible||high||very high||high|
Status and delays 
Several delays in production have occurred and there has not been a public demonstration of the uniquely high energy density claims of the inventors. This has led to the speculation that the claims are false. In January 2007 EEStor stated in a press release "EEStor, Inc. remains on track to begin shipping production 15 kilowatt-hour Electrical Energy Storage Units (EESU) to ZENN Motor Company in 2007 for use in their electric vehicles." In September 2007, EEStor co-founder Richard Weir told CNET production would begin in the middle of 2008. In August 2008, it was reported he stated "as soon as possible in 2009". ZENN Motor Company (ZMC) denied there was a delay, just a clarification of the schedule, separating "development" and "commercialization". In March 2008 Zenn stated in a quarterly report a "late 2009" launch was scheduled for an EEStor-enabled EV. In December 2009 Zenn announced that production of the lead acid based ZENN LSV would end April 30, 2010. At that time Zenn did not announce a date for production of an EEstor based car.
In April 2009 EEStor announced third-party certification of permittivity. The press release did not mention the voltage at which it was tested, so EEStor's uniquely high energy density claims remain to be demonstrated.
In July 2009 ZENN Motor Company, as a result of the April 2009 permittivity tests, invested an additional $5 million in EEStor, increasing its share of ownership to 10.7%. A Zenn press release indicates they were able to get a 10.7% stake because other EEStor investors did not increase their stake.
In January 2013 EEStor released a press release that included test results of four samples of dielectric layers tested by System Engineering and Laboratories ("SEAL"). One sample showed a permittivity of 162,291 and an energy density (dielectric layer only) of 73.90 (W.h/L). This sample was tested at 1500 volts.
Skepticism from experts 
EEStor's claims for the EESU exceed by orders of magnitude the energy storage capacity of any capacitor currently sold. Many in the industry have expressed skepticism about the claims. Jim Miller, vice president of advanced transportation technologies at Maxwell Technologies and capacitor expert, stated he was skeptical because of current leakage typically seen at high voltages and because there should be microfractures from temperature changes. He stated "I'm surprised that Kleiner has put money into it."
Patent description and claims 
EEStor reports a large relative permittivity (19818) at an unusually high electric field strength of 350 MV/m, giving 10,000 J/cm³ in the dielectric. Voltage independence of permittivity was claimed up to 500 V/μm to within 0.25% of low voltage measurements. Variation in permittivity at a single voltage for 10 different components was claimed by measurements in the patent to be less than +/- 0.15%. If true, their capacitors store at least 30 times more energy per volume than (other) cutting-edge methods such as nanotube designs by Dr Schindall at M.I.T., Dr. Ducharme's plastics research, and breakthrough ceramics discussed by Dr. Cann. In such a strong electric field, the permittivity usually decreases due to dielectric saturation, or the dielectric may break down, causing a short circuit between the capacitor electrodes. Northrop Grumman and BASF have also filed patents with similar theoretical energy density claims. EEStor has the only patent which claims to have actually measured the high energy density in sample components.
The EEStor patents cite a journal article and a Philips Corporation patent as exact descriptions of its "calcined composition-modified barium titanate powder." The Philips patent describes "doped barium-calcium-zirconium-titanate" (CMBT) and reports a permittivity of up to 33,500 at 1.8 V/μm, but does not report the permittivity at high electric fields such as the 350 V/μm EEStor claims. EEStor coats its 0.64 micrometer (average size) CMBT particles with 10 nm aluminum oxide (6% by volume) and immerses them in 6% PET plastic by volume, giving 88% CMBT. The patent claims the aluminum oxide coating and PET matrix reduce the net permittivity to 88% of the CMBT permittivity. The Philips patent did not use either aluminum oxide or PET. The dielectric in solution is screen-printed and dried in 10 μm layers, alternating with 1 μm aluminum plates (used to apply the working 3500 V).
A July 2008 press release states the PET plastic matrix allows for better crystal polarization and that this "along with other proprietary processing steps provides the potential of a polarization saturation voltage required by EEStor, Inc." The patent states this is done at 180 C with 4000 V.
EEStor's US patent 7033406 mentions aluminum oxide and calcium magnesium aluminosilicate glass as coatings, although their subsequent US patent 7466536 mentions only aluminum oxide. Nickel was mentioned in the earlier US patent as the electrode but the later patent uses 1 μm aluminum plates as a less expensive alternative. According to the patents, both changes were made possible by selecting the PET matrix because it is pliable enough to fill voids at only 180 C.
In April 2007, ZENN Motor Company, a Canadian electric vehicle manufacturer, invested $2.5 million in EEStor for 3.8% ownership and exclusive rights to distribute their devices for passenger and utility vehicles weighing up to 1,400 kg (excluding capacitor mass), along with other rights. In July 2009, Zenn invested another $5 million for a 10.7% stake. A Zenn press release indicates they were able to get a 10.7% stake because other EEStor investors did not increase their stake. Zenn has received $34 million from the equity markets in the past 3 years, and spent $10.1 million of the proceeds on EEStor ownership and technology rights. In December 2009 Zenn canceled plans for the car but plans to supply the drive train. By April 2010, Zenn had cancelled all production of electric vehicles, leaving ownership of EEStor and their rights to the technology as their focus. Zenn raised CAD$2 million in April of 2012, mostly on the promise of EEStor's technology.
In January 2008, Lockheed-Martin signed an agreement with EEStor for the exclusive rights to integrate and market EESU units in military and homeland security applications. In December 2008, a patent application was filed by Lockheed-Martin that mentions EEStor's patent as a possible electrical energy storage unit.
In September 2008, Light Electric Vehicles Company announced an agreement with EEStor to exclusively provide EEStor's devices for the two and three wheel market.
- "Signs Agreement with EESTOR, Inc., for Energy Storage Solutions". Lockheed Martin. 2008-01-09. Retrieved 2009-09-21.
- US patent 7033406, Weir; Richard Dean & Nelson; Carl Walter, "Electrical-energy-storage unit (EESU) utilizing ceramic and integrated-circuit technologies for replacement of electrochemical batteries", published 25 April 2006, issued 25 April 2006, assigned to EEStor, Inc
- US patent 7466536, Weir; Richard Dean & Nelson; Carl Walter, "Utilization of poly(ethylene terephthalate) plastic and composition-modified barium titanate powders in a matrix that allows polarization and the use of integrated-circuit technologies for the production of lightweight ultrahigh electrical energy storage units (EESU)", published 16 December 2008, issued 16 December 2008, assigned to EEStor, Inc
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- WO application 2008156903