Abstract
Electrolyte and separator are two vital components in supercapacitors. High safety is one of the major advantages of polymer electrolyte, which means, even in extreme environment or during faulty, polymer electrolyte will not release any harmful gas or liquid. Mediators are a pair of compounds which can reciprocal transform by losing and gaining electrons. Thus, doping mediators in polymer electrolyte will improve the electronic conductivity. Use of the mediator doped electrolytes in the electrode matrix will benefit the transport process in supercapacitors. However, these electrolytes should not be used in the separators. Polyvinylidene fluoride (PVDF) and lithium trifluoromethanesulfonate (LiTFS) was selected as polymer electrolyte. One mediator couple are potassium ferrocyanide (K
3
Fe(CN)
6
) and potassium ferricyanide (K
4
Fe(CN)
6
). Another couple are iodine (I
2
) and sodium iodide (NaI). Conductivity of the membranes were measured with an device as shown in Figure 1. Results of electronic conductivity versus the concentration of mediators are given in Figure 2 and results of ionic conductivity versus the concentration of mediators are given in Figure 3. Electronic conductivity of membranes is enhanced from 10
-7
S/cm level to 10
-4
S/cm level by increasing the concentration of mediators from 0% to 5%. In the I
2
/NaI mediator doped membrane the electronic conductivity continuously increase with increasing the concentration above 5%. However, in the K
3
Fe(CN)
6
/ K
4
Fe(CN)
6
. doped membrane the electronic conductivity is a constant above 5%. Ionic conductivity of membranes is stayed on 10
-2
S/cm level. The authors use the electron exchange mechanism and site percolation theory to explain the phenomenon.
Figure 1