D. Dunn et J. Newman, Predictions of specific energies and specific powers of double-layer capacitors using a simplified model, J ELCHEM SO, 147(3), 2000, pp. 820-830
A model based on dilute-solution porous-electrode theory is proposed to des
cribe electrochemical devices that store energy in the double layer (double
-layer capacitors). Various assumptions, such as neglecting concentration p
olarization, potential-dependent capacitance, and micropore effects, are ma
de in the model. For constant-current discharges, the model reduces to a re
sistance-capacitance (RC) series circuit model after the initial dischargin
g transients. The RC series circuit model is seen to fit existing experimen
tal data for the discharge times available. The specific energy for constan
t-current and constant-power discharges is maximized over a range of discha
rge times by optimizing the electrode thickness, electrode porosity, and th
e final voltage constrained by the cutoff voltage. This maximization allows
predictions of the attainable specific energies and powers for these devic
es and shows the influence of the various cell properties. Energy efficienc
ies are found for cycles when the capacitor is discharged in a given time a
nd then charged infinitely slowly, and when the capacitor is discharged and
charged in the same amount of time. Limitations to the model are discussed
. (C) 2000 The Electrochemical Society. S0013-4651(99)05-100-9. All rights
reserved.