A Closer Look At EEStor, the Capacitor Company

EEStor is a company based in Cedar Park, Texas, United States that claims to have developed a revolutionary new type of capacitor for electricity storage, which EEStor calls the 'Electrical Energy Storage Unit' (EESU). EEStor claims the EESU can store far more electrical energy than any other type of capacitor, and that it could be used to propel a small car for about 300 miles. This potential for making electric vehicles fully competitive with gasoline-powered vehicles has created much interest, although the company's claims have yet to be verified. EEStor's CEO and president is Richard Weir, who is also a co-inventor named on two of the company's patents.

EEStor's proposed future product would be a ceramic-based unit fabricated with integrated-circuit techniques. The technology, described in EEStor's patent, involves sintering very small grains of coated barium titanate powder into a bulk ceramic. The process is intended 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, EEStor intends to make the bulk ceramic have properties similar to those of individual barium titanate crystals. To keep costs down, the sintering is proposed to occur at low temperatures, enabling the manufacturer to use aluminum electrodes instead of more expensive nickel or platinum electrodes.

The technical specifications of the EESU would be, according to:

	Prototype / Low Volume	LightEVs Estimate	Mass Production
Energy density (Wh/l)	606	700	1513
Specific energy (Wh/kg)	273	450	682
Price ($ USD/kWh)	$61	n/a	$40

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

	Ceramic EESU	NiMH	Lead-acid(Gel)	Lithium-ion
Weight (kg/lbs)	135/300	780/1716	1660/3646	340/752
Volume (litres/cubic inches)	74.5/4541	293/17,881	705/43,045	93.5/5697
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
Hazardous Materials	none	yes	yes	yes
Temperature vs. effect on energy storage	negligible	high	very high	high

The claims made 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. This is half the price per stored watt-hour of 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.
• The unit will come equipped with a built in Buck-boost converter (DC-DC voltage converter) to provide the proper input/output voltage
• A self-discharge rate of 0.1% per month

The company appears to be proceeding with development.

The capacitance of the device described in the patent is 30.693 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

which gives a total energy storage of 185.31 MJ or 51.48 kWHours.