power density ultracapacitor energy storage device

Example design parameters:

The energy stored in the Capacitor: E=½ CV2 where C is the capacitance (F) and V is the charging voltage.

  • Energy needed: 85 kWh
  • Charging voltage V=600
  • Relative permittivity k=16 million (This is the highest value for dielectric constant reported in open literature. In comparison, EEStor uses material with a dielectric constant of 18,000 for their solid-state battery development.
  • Area of a single layer capacitor A=20cm x 20 cm=400 cm2
  • Thickness of the dielectric t=20 x10-6

For a unit of 85 kWh the total capacitance (called geometrical capacitance) is:

  • C= 2E/V2 = 2 x 85 000 x 3600/(600)2 =1,700 F

Capacitance ONE layer (=Ԑ0*kA/t)

0.2832 F/layer

Energy density:

5,900 Wh/lit

Specific Energy Density:

1,734 Wh/kg

Gravimetric Power Density | frequency is 1

7,780 W/kg

Total weight energy storage device (only stacked layers | housing not included)

49 kg

Discharging depends on load:

There are many advantages of solid state devices over Li-Ion batteries (no environmental pollution, millions of
charging and discharging cycles and very fast charging to mention a few) the only disadvantage of super
capacitor is the inability to hold the steady voltage during the discharging cycle under load.

The voltage in super capacitor will decrease steadily and the rate of voltage decrease depends on the load.


Higher loads will cause the voltage to drop faster. The solution to this problem is to fabricate higher power
unit with high energy density. With high power density (high kWh/kg) super capacitors, it would be possible to
put on board several units and discharge one unit after another until the voltage in each unit drops below a
certain value.


In this way it will be possible to keep the voltage high during the entire life of the battery set. This
can easily be done using today’s modern electronics.

Ceramic based single layer energy storage device.

High capacitance dielectric

Breakthrough ceramic/metal with 16 x106 dielectric constant.

Due to the nature of material (the charge is stored on the surface of the dielectric/metal) charging the capacitor depends on the power to be stored. If the power is low (several kWh) charging is done in seconds.


If the power is high, e.g. 50 or 80 kWh, charging can take several minutes provided the charging station has high enough voltage and current. Charging of several layers, as already demonstrated in our lab, have shown a full charge of the layers in less than a second.

Self-discharging Li-Ion batteries:
Self-discharging of Li-Ion Battery discharges is about 5 percent in the first 24 hours and then loses 1–2 percent
per month; the protection circuit adds another 3 percent per month. In general, the self-discharge of all battery
chemistries increases at higher temperature, and the rate typically doubles with every 10°C (18°F).


A noticeable energy loss occurs if a battery is left in a hot vehicle. High cycle count and aging also increase self-discharge of all systems.

Predicted self-discharging of UltraCaps's ESD:
The self-discharging of super capacitor is similar to Li-Ion Battery except that the temperature effect is smaller
and the device should be able to hold the charge for up to 20-30 days. EEStor claims their unit to be able to
hold the electricity for 2 to 3 months.