EEStor

EEStor is a company based in Cedar Park, Texas, United States that claims to have developed a capacitor for electricity storage, which EEStor calls the 'Electrical Energy Storage Unit' (EESU). Key to the increased energy density of the device is not improved charge density, but dramatically higher operating voltages. The company claimed that the EESU stored more energy than lithium-ion batteries at a lower cost than lead-acid batteries used in gasoline-powered cars. Such a device would revolutionize the electric car industry. Experts always said such claims were far from being realistic, and eventually, in late 2014, these claims have been shown to be over 100 times more than what the technology is actually capable of.

The claims are described in detail in two of the company's patents, US 7033406  and US 7466536 .

The following is how the EESU is claimed to compare to electrochemical batteries used for electric cars:

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.

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