(added the references sections.... btw check out Rod's (connected to Appropedia) great work - http://www.sciencedaily.com/releases/2008/09/080916143910.htm)
No edit summary
Line 14: Line 14:
====Al Foil Current Collector====
====Al Foil Current Collector====


Electrodes for supercapacitors are commonly built on Al foil in the 100 - 300 um region to act as the current collector for the electrodes. As the power delivery potential of the device depends largely on the equivalent series resistance (ESR) of the supercapacitor, any reduction in impedance of the current collector will yield immediate power delivery improvements. This is readily apparent in the equation show below which is valid for a voltage in the capacitor between 1 and 1/2 of its rating <ref>Burke, Andrew. "Ultracapacitors: why, how, and where is the technology." Journal of Power Sources 91(2007): 37-50</ref>.  
Electrodes for supercapacitors are commonly built on Al foil in the 100 - 300 um region to act as the current collector for the electrodes. As the power delivery potential of the device depends largely on the equivalent series resistance (ESR) of the supercapacitor, any reduction in impedance of the current collector will yield immediate power delivery improvements. This is readily apparent in the equation show below which is valid for a voltage in the capacitor between full and 1/2 of its rating <ref>Burke, Andrew. "Ultracapacitors: why, how, and where is the technology." Journal of Power Sources 91(2007): 37-50</ref>.  


P_p_e_a_k = \frac{9}{16}*(1-EF)*V_o^{2}/R_E_S_R
P_p_e_a_k = \frac{9}{16}*(1-EF)*V_o^{2}/R_E_S_R
Line 27: Line 27:
# Remove and rinse with distilled water
# Remove and rinse with distilled water


What was found is that the average roughness of the Al foil increased from 0.2-0.3 um to 2.5-2.6 um with channels varying from 10-15 um deep <ref>Portet, C., P.L. Taberna, P. Simon, C. Laberty-Robert. "Modification of Al current collector surface by sol–gel deposit for carbon–carbon supercapacitor applications." Electrochimica Acta 49(2004): 905–912</ref>. This was likely due to the nucleation sites developed by the NaOH solution, and the subsequent dissolution of Al caused by the HCl bath with the anodic current. This is substantiated by the fact that the potential of the Al foil substantially increased after the first second of current being applied, suggesting an increased dissolution of Al <ref>Portet, C., P.L. Taberna, P. Simon, C. Laberty-Robert. "Modification of Al current collector surface by sol–gel deposit for carbon–carbon supercapacitor applications." Electrochimica Acta 49(2004): 905–912</ref>. As a consequence of this Al surface dissolution, the specific surface area of the Al foil increased as compared to the original Al foil. When combined with the active material in the supercapicitor, the larger surface area allows for more contact between the current collector and the electrode.
What was found is that the average roughness of the Al foil increased from 0.2-0.3 um to 2.5-2.6 um with channels varying from 10-15 um deep <ref>Portet, C., P.L. Taberna, P. Simon, C. Laberty-Robert. "Modification of Al current collector surface by sol–gel deposit for carbon–carbon supercapacitor applications." Electrochimica Acta 49(2004): 905–912</ref>. This was likely due to the nucleation sites developed by the NaOH solution, and the subsequent dissolution of Al caused by the HCl bath with the anodic current. This is substantiated by the fact that the potential of the Al foil substantially increased after the first second of current being applied, suggesting an increased dissolution of Al <ref>Portet, C., P.L. Taberna, P. Simon, C. Laberty-Robert. "Modification of Al current collector surface by sol–gel deposit for carbon–carbon supercapacitor applications." Electrochimica Acta 49(2004): 905–912</ref>. As a consequence of this Al surface dissolution, the specific surface area of the Al foil increased as compared to the original Al foil. When combined with the active material in the supercapicitor, the larger surface area allows for more contact between the current collector and the electrode. This decreases the ESR of the supercapacitor, and therefore increases the specific power output.


====Carbon Nanotubes====
====Carbon Nanotubes====

Revision as of 19:25, 14 November 2008

Template:MECH370 A W is an energy storage devices with the ability to be charged and discharged very quickly, with little to no degradation in performance with an increase in number of charge/discharge cycles. Because of this property, supercapacitors bridge the gap between long term energy storage provided by a conventional electrochemical W, and short term, high current energy demands provided by a standard dielectric W.

The problem with supercapacitors is that they still have a relatively high cost per Watt-hour of energy storage potential. Depending on the design, which can rely on Carbon/Carbon electrodes or metal oxide electrodes, material costs can severely hamper the cost benefit of employing supercapacitors in these power demand situations. In the Carbon/Carbon case, this is primarily due to the use of an expensive specially prepared high surface area carbon particulate or cloth that can cost US $50-100/kg [1]. Decreasing the cost by a factor of 10 is required in order to increase the market size for supercapacitors.

Factors affecting performance

The tradeoff between energy density and the RC time constant is an important design consideration. Often, a lower energy density (W-h/kg) is required in order to lower the RC time constant, and in turn, increase the power capability (W/kg) of the supercapacitor.

The performance of a supercapacitor is often dependent on the internal resistance characteristics of the device. A good understanding of the impedance of the supercapacitor is required in order to design a system with a matched impedance load type. A lowering of the W or ESR is critical in increasing the specific power output of the supercapacitor.

New technologies

Work is being done on new metal oxides and carbon types for supercapacitor electrodes which will potentially decrease the cost of the supercapacitors with minimal decrease in performance [2]. Two of these major studies involve the use of W (CNT) as the electrode in the supercapacitor, and the use of an Al foil to act as the current collector [3].

Al Foil Current Collector

Electrodes for supercapacitors are commonly built on Al foil in the 100 - 300 um region to act as the current collector for the electrodes. As the power delivery potential of the device depends largely on the equivalent series resistance (ESR) of the supercapacitor, any reduction in impedance of the current collector will yield immediate power delivery improvements. This is readily apparent in the equation show below which is valid for a voltage in the capacitor between full and 1/2 of its rating [4].

P_p_e_a_k = \frac{9}{16}*(1-EF)*V_o^{2}/R_E_S_R

Where P is the peak power output of the supercapacitor, EF is the efficiency of the power pulse, V is the voltage across the supercapactitor, and R is the equivalent series resistance of the supercapacitor.

Research was done to find out how to decrease this ESR resistance in the Al current collectors. The steps taken are as follows

  1. 4 cm+2, 200 um thick Al foil is bathed in 1 molar NaOH electrolyte for 10 minutes
  2. Remove and rinse with distilled water
  3. Samples were then placed in 1 molar HCl at 80 degrees Celsius with a constant 200mA/cm^2 anodic current for 20 seconds.
  4. Remove and rinse with distilled water

What was found is that the average roughness of the Al foil increased from 0.2-0.3 um to 2.5-2.6 um with channels varying from 10-15 um deep [5]. This was likely due to the nucleation sites developed by the NaOH solution, and the subsequent dissolution of Al caused by the HCl bath with the anodic current. This is substantiated by the fact that the potential of the Al foil substantially increased after the first second of current being applied, suggesting an increased dissolution of Al [6]. As a consequence of this Al surface dissolution, the specific surface area of the Al foil increased as compared to the original Al foil. When combined with the active material in the supercapicitor, the larger surface area allows for more contact between the current collector and the electrode. This decreases the ESR of the supercapacitor, and therefore increases the specific power output.

Carbon Nanotubes

Double walled carbon nanotubes (DWNT) are used in a mixture with activated carbon to form the electrode for the supercapacitor. A mixture consisting of

References

  1. ↑ Burke, Andrew. "Ultracapacitors: why, how, and where is the technology." Journal of Power Sources 91(2007): 37-50
  2. ↑ Burke, Andrew. "Ultracapacitors: why, how, and where is the technology." Journal of Power Sources 91(2007): 37-50
  3. ↑ Portet, C., P.L. Taberna, P. Simon, E. Flahaut, C. Laberty-Robert. "High power density electrodes for Carbon supercapacitor applications." Electrochimica Acta 50(2005): 4174-4181.
  4. ↑ Burke, Andrew. "Ultracapacitors: why, how, and where is the technology." Journal of Power Sources 91(2007): 37-50
  5. ↑ Portet, C., P.L. Taberna, P. Simon, C. Laberty-Robert. "Modification of Al current collector surface by sol–gel deposit for carbon–carbon supercapacitor applications." Electrochimica Acta 49(2004): 905–912
  6. ↑ Portet, C., P.L. Taberna, P. Simon, C. Laberty-Robert. "Modification of Al current collector surface by sol–gel deposit for carbon–carbon supercapacitor applications." Electrochimica Acta 49(2004): 905–912
Retrieved from "https://www.appropedia.org/w/index.php?title=Increasing_supercapacitor_performance&oldid=57013"
Cookies help us deliver our services. By using our services, you agree to our use of cookies.