Supercapacitors symmetrical

In the third paper by French and Ukrainian scientists (Khomenko et al.), the authors focus on high performance a-MnCVcarbon nanotube composites as pseudo-capacitor materials. Somewhat surprisingly, this paper teaches to use carbon nanotubes for the role of conductive additives, thus suggesting an alternative to the carbon blacks and graphite materials - low cost, widely accepted conductive diluents, which are typically used in todays supercapacitors. The electrochemical devices used in the report are full symmetric and optimized asymmetric systems, and are discussed here... 

The most known supercapacitor is the symmetric one, i.e., with two identical electrodes immersed in an aqueous or an organic electrolyte (Figure 8.2). The two electrodes are separated by a porous membrane (paper, glass fiber, polymer) named separator. In the industrial capacitors, the electrode... 

As it was already described in Section 8.2.1, the total capacitance of a supercapacitor is given by Equation 8.1. In a symmetric capacitor with equal values of capacitance for the positive (Cj) and negative (f2) electrodes, the total capacitance of the system is half the capacitance of one electrode. In the asymmetric device, as the capacitance of the battery electrode is much higher than the capacitive one, the capacitance of the system approaches that of the electrode with the smallest value. In other words, the capacitance of the asymmetric configuration combining a battery-like electrode with a capacitive one will be close to the value of the capacitive electrode, i.e., twice larger than that for a symmetric configuration with two capacitive electrodes. 

Table 8.5 summarizes the electrochemical performance of different types of symmetric and asymmetric supercapacitors in aqueous medium, including the maximum cell voltage (Vmax), the... 

Figure 10. Symmetric supercapacitor with composite poly(3-methylthiophene)-carbon-binder electrodes, a) Delivered charge ( ) and coulombic efficiency (o) of galvanostatic cycles (from 2000th to 5000th) at 5 mA cm between 0 and 3.1 V b) potential profiles of supercapacitor (solid line), and of positive (broken line) and negative (dotted line) electrodes during the 2000th galvanostatic cycle.

Structural formulas of some PT derivatives are shown in Figure 28.3. PT can be both n-doped and p-doped. As follows from Table 28.3, anodic capacitance (under p-doping) of PT derivatives is higher than its cathodic capacitance (under n-doping). Therefore, the cathode in PsCs of type III must be thicker than the anode. It was found that conductivity in the n-doped form is lower than in the p-doped form conductivity in the n-doped form is rather low. Most of PT derivatives are stable in air and in a moist state both in the p-doped and undoped forms. Symmetrical type HI supercapacitors with PT derivatives on both electrodes were manufactured. Herewith, the energy density of 30-40 Wh/kg and power density of 5-10 kW/kg per mass of active materials was reached. Table 28.3 shows the characteristics of PsCs based on poly-3-(3,4-difluorophenyl)thiophene (PDFPT) and poly-3-(4-cyanophenyl)thiophene (PCPT). One can see that rather high energy density values were obtained in this case (Table 28.5). 

As follows from these tables, symmetrical double-layer supercapacitors based on C/C-type carbon electrodes and, in limited quantities, some hybrid C/NiOOH-type ECSCs are produced at present. In the case of pseudocapacitors based on electron-conducting polymers, there are as yet only laboratory prototypes. 

FIG U RE 2.15 CVs at 5 mV s of symmetric capacitor based on the (a) Glu-(NH4)3P04-800 and (b) GIU-NH4CI-8OO in 6 M KOH. (Reprinted from Journal of Power Sources, 239, Wang, C. et al., Sustainable synthesis of phosphorus- and nitrogen-co-doped porous carbons with tunable surface properties for supercapacitors, 81-88, Copyright 2013, with permission from Elsevier.)... 

Yuan, C., L. Hou, D. Li, Y. Zhang, S. Xiong, and X. Zhang. 2013. Unusual electrochemical behavior of Ru-Cr binary oxide-based aqueous symmetric supercapacitors in KOH solution. Electrochimica Acta 88 654-658. 

Ataherian, R, and N. L. Wu. 2011.1.2 Volt manganese oxide symmetric supercapacitor. Electrochemistry Communications 13 1264-1267. 

Sun, W., R. Zheng, and X. Chen. 2010. Symmetric redox supercapacitor based on micro-fahrication with three-dimensional polypyrrole electrodes. Journal of Power Sources 195 7120-7125. 

Kalubarme, R. S., H. S. Jadhav, and C. J. Park. 2013. Electrochemical characteristics of two-dimensional nano-structured MnOj for symmetric supercapacitor. Electrochimica Acta 87 457-465. 

Yigit, D., M. Giillii, T. Yumak, and A. Sinag. 2014. Heterostructuredpoly(3,6-dithien-2-yl-9H-carbazol-9-yl acetic acid)/Ti02 nanoparticles composite redox-active materials as both anode and cathode for high-performance symmetric supercapacitor applications. Journal of Materials Chemistry A 2 6512-6524. 

Maiti, S., A. Pramanik, and S. Mahanty. 2014. Interconnected network of Mn02 nanowires with a cocoonlike morphology Redox couple-mediated performance enhancement in symmetric aqueous supercapacitor. ACS Applied Materials Interfaces 6 10754-10762. 

Bhat D. K, Kumar M. S., N and p doped poly[3,4-ethylenediox34hi-ophene] electrode materials for symmetric redox supercapacitors,/ Mater. Sci., 2007,42,8158-8162. 

---