TAILIEUCHUNG - Electrostatic Solid-State Capacitors

Conventional electrostatic capacitors contain a dielectric instead of an electrolyte solution. Electrochemical supercapacitors, however, contain a liquid electrolyte (aqueous, nonaqueous), and can be classified by the electrode material used (carbon, metal oxide, polymer) and the operating principle (double-layer capacitance, redox pseudocapacitance, hybrid capacitance). | Electrostatic Solid-State Capacitors P Kurzweil University of Applied Sciences Amberg Germany 2009 Elsevier . All rights reserved. Electrostatic and Electrochemical Energy Storage Conventional electrostatic capacitors contain a dielectric instead of an electrolyte solution. Electrochemical supercapacitors however contain a liquid electrolyte aqueous nonaqueous and can be classified by the electrode material used carbon metal oxide polymer and the operating principle double-layer capacitance redox pseudocapacitance hybrid capacitance . Nonfaradaic electrochemical double-layer capacitors EDLCs based on carbon electrodes come close to electrostatic capacitors but they show a pseudocapacitance in reality as well. A classification of supercapacitors is shown in Figure 1. Electrochemical Capacitors Ideal case Conventional capacitors store energy in an electric field which is modified by a dielectric. Batteries utilize electrochemical redox reactions which involve mass transfer moving ions . Electrochemical double-layer capacitors employ both principles. The phase boundary between an electronic conductor electrode and a liquid ionic conductor electrolyte behaves like a plate capacitor with a nanometer-thin dielectric the so-called Helmholtz layer. The ideal EDLC operates as a purely physical device without charge transfer reactions or volume changes of active materials undergoing chemical transformations during charge and discharge. Regular double-layer capacitance arises from the potential dependence of the surface density of charges stored electrostatically at the solid-liquid interface. On the capacitor electrodes the accumulated charge Qis a combination of an excess or deficit of conduction-band electrons in the nearsurface region of the interface and the counterbalancing charge densities of accumulated cations or anions in the electrolyte on the solution side. The interface is assumed to be completely blocking that is there is no current flowing across the double

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