Q2. What is the main problem in developing ultracapacitors?
In progressing from small laboratory cells to larger, multi-electrode or multi-cell devices, packaging has been a problem in developing ultracapacitors, because of their inherent low energy density and need for very low resistance to have a clear power density advantage compared with batteries.
Q3. What are the advantages of ultracapacitors as pulse power devices?
relative to batteries, the advantages of ultracapacitors as pulse power devices are high power density, high efficiency, and long shelf and cycle life.
Q4. What is the effect of reducing the maximum voltage of the unit on its useable energy density?
Since the energy stored in the unit is proportional to its voltage squared, reducing the maximum voltage of the unit will have a significant effect on its useable energy density.
Q5. What are the primary uncertainties concerning the hybrid capacitors?
The primary uncertainties concerning the hybrid capacitors are their shelf and cycle life due to the use of battery-like positive electrodes.
Q6. How many kWrkg of power density is expected to be used in the hybrid capacitors?
Based on the low resistance of the thin electrodes using aqueous electrolytes, it seems likely that the peak power densities of the devices will be at least several kWrkg.
Q7. How does the resistance of the electrode in an ultracapacitor be determined?
The electronic resistivity of the electrode in an ultracapacitor must be less than 1 mV-cm if the resistance of the cell is to be low.
Q8. Why is material purity important for ultracapacitors?
Material purity is particularly important for ultracapacitors because it strongly affects both their leakage current and life characteristics.
Q9. What is the critical factor in the cost of the ultracapacitor?
The most critical factor in the cost of the ultracapacitor is the cost of the electrode material, which in many cases is high surface area, speciality carbon particulate or cloth.
Q10. How many micropores should be used to meet the power requirements?
In order to meet these power requirements, the electrode thickness should be less than 150 mm and a large fraction of the micropores should have a ˚diameter of at least 10–20 A.
Q11. What are the applications of electrical energy storage?
Electrical energy storage is required in many applications — telecommunication devices, such as cell phones and pagers, stand-by power systems, and electricrhybrid vehicles.
Q12. What is the primary reason for the low energy density of the devices with the low RC time?
The primary reason for the higher power and relatively low energy density of the devices with the low RC time constant is that they utilize much thinner elecŽtrodes with the result that the inactive components current .collector, separator and packaging are a much greater fraction of the device weight.
Q13. How much ruthenium oxide is needed for small devices?
For small devices, the weight of ruthenium oxide needed is only a fraction of a gram so that the cost of the materials would be quite low.
Q14. Why have ultracapacitors been built using the monoblock approach?
Most ultracapacitor devices have been built using the monoblock approach, because the quality control required is less demanding and the packaging and assembly are simpler.
Q15. What is the specific capacitance of the hydrous ruthenium oxide?
The high specific capacitance is thought to be due to the intercalation of the Hq ions into the bulk of the hydrous oxide making the specific capacitance much less sensitive to surface area than was the case w xwith the anhydrous oxide.
Q16. What is the energy density of the devices using lead oxide for the positive electrode?
The energy density claimed for the devices using lead oxide for the positive electrode are 10–20 W hrkg for a voltage range of 0.7–1.8 V.
Q17. What is the common method of joining the electrode to a current collector?
This requires a very high conductivity adhesive or a bonding process that chemicallyjoins the electrode material to the current collector material, which is usually a metal foil, either nickel or aluminum.
Q18. How do you separate energy and power requirements?
As power requirements for many applications become more demanding, it is often reasonable to consider separating the energy and power requirements by providing for the peak power Ž .by using a pulse power device capacitor that is charged Ž .periodically from a primary energy storage unit battery .
Q19. What is the way to increase the energy density of the ultracapacitors?
The calculated results indicate that there is considerable potential for increasing the energy density and maximum power of ultracapacitors using carbon andorganic electrolytes from that of the best of the present devices.
Q20. What is the difference in capacitance between organic and aqueous electrolytes?
The result of these differences in electrolyte properties is that ultracapacitors using organic electrolytes must much thinner electrodes than those using aqueous electrolytes and thus lower capacitance per electrode area.
Q21. Why are the power densities more difficult to estimate?
The power densities are more difficult to estimate with reasonable confidence because of the uncertain contributions of the pore resistance of the carbon andthe contact resistances at the electrodercurrent collector interfaces to the total resistance of the device.