Sách Electrochemical Capacitors: Ionic Liquid Electrolytes

Double-layer carbon supercapacitors (electrochemical
double-layer capacitor (EDLCs)) based on two carbon
electrodes of high surface area separated by an electrolyte
are the most popular electrochemical supercapacitors. The
charge process is electrostatic with charge separation at
the two electrode–electrolyte interfaces. The EDLCs can
thus be modeled with two capacitances in series with what
is called equivalent series resistance (ESR). Given that the
electrode capacitance depends on the reciprocal of the
double-layer thickness, which is on the order of 1010
m,and that it is directly related to the carbon surface area,
typically of several hundred square meters per gram of
carbon, the capacitance of EDLCs is significantly higher
than that of the dielectric and electrolytic capacitors. The
stored energy of EDLCs is also higher than that of the
dielectric and electrolytic capacitors, but it is lower than
that of batteries. Indeed, the faradic charge processes in
batteries involve all the bulk electrode materials and not
just the surface. The maximum energy (Emax)ofEDLCis
directly related to its capacitance (Csc) and to the square of
the maximum cell voltage (Vmax) as in the following
equation: