Type II supercapacitor

Relatively little work has been published on Type II supercapacitors. Arbizzani et al. [147] have prepared PPy/poly(3-methylthiophene) devices performance was similar to their PPy-based Type I device and to carbon supercapacitors. Clemente et al. [163] prepared PPy/PANI devices with specific capacitance values as high as 25 F/g, depending on electrolyte composition. Stenger-Smith et al. [37] prepared poly(3,4-ethylenedioxythiophene) (PEDOT, Figure 9.4J)/poly(3,4-propylenedioxythiophene) (PProDOT, Figure 9.4L) Type II supercapacitors. Switching speed and cycle life were found to depend heavily on electrolyte composition, with only 2% loss in capacity over 50,000 full cycles when 1-ethyl-3- methyl-IH-imidazolium bis(trifluoromethanesulfonyl)imide (EMI-BTI) was used as the electrolyte. 

Figure 9 shows the discharge curves of a Type I polypyrrole-based, a Type II polypyrrole/poly(3-methylthiophene)-based and a Type III poly(dithieno[3,4-6 3, 4 -d]thiophene-based supercapacitor at 4 mA cm discharge current. Types I and II can be assembled using such conventional heterocyclic polymers as polypyrrole, polyaniline and polythiophene, which are efficiently p-dopable polymers and can easily be chemically or electrochemically synthesized from inexpensive... 

FIGURE 9.7 Charging of a Type II EAP supercapacitor. (Adapted from Rudge, A. et al., /. Power Sources, 47, 89, 1994. With permission. Copyright 1994, from Elsevier.)... 

Several other polymers have also been evaluated for use in Type I supercapacitors. While polythiophene exhibits an excellent specific capacitance for energy storage (250 F/g) [160], polythiophene supercapacitors are uncommon, possibly due to cycle life issues. However, derivatives of polythiophene have been used in the preparation of Type II, Type III, and Type IV supercapacitors (see Section 9.3.6.2 and Section 9.3.6.3). 

FIGURE 9.9 Comparison of voltage decay characteristics for Type I, Type II, and Type III and IV supercapacitors. 

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