EEStor is a company based in Cedar Park, Texas, United States that has developed a type of capacitor for electricity storage, which EEStor calls ‘Electrical Energy Storage Units’ (EESU). The EEStor EESU is an integral part of the ZENNergy drive-train. Its CEO and president is Richard Weir, who is also a co-inventor named on their principal technology patent.
According to its patent application, these units will use high-purity 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 of the prototype is 1 MJ/kg; existing commercial supercapacitors typically have an energy density around 0.02 MJ/kg, while lithium ion batteries are around 0.54–0.72 MJ/kg. For comparison, gasoline has an energy density around 45 MJ/kg. However, the combustion process is unable to extract the majority of this energy and overall energy delivered to the wheel is typically less than 20% of this value; a value of 9 MJ/kg is more indicative. EEStor has stated that production examples should be about 2.5 MJ/kg, better than 1/4th the usable energy density of gasoline. This would represent an enormous leap in energy storage technology, which is the reason the company generates so much excitement and skepticism at the same time. (As part of the review process for patents, the U.S. Patent Office does not test the validity of the technical assertions in the patent application. Instead, it only checks whether earlier publications disclose the same idea.)
Based on these claims, a full charge should give the capacitor sufficient energy to drive a small car 300 miles (480 km). Although the technology should allow very fast charging (e.g., 5 minutes), 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. Overnight charging at home should still be practical, 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 – and deliver cheap electric power to the house too, making expensive peak power plants obsolete. 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 (400 km) range and a normal household outlet with 220 volt supply can fully charge the EEStor powered CityZENN in 2 hours for a 250-mile (400 km) range.