Capacitance retention

Mesoporous carbons were manufactured using MgO particles as a template. This process has a number of advantages because MgO particles can be dissolved in a weak acid, such as citric acid, and can be used again as the initial template and therefore carbons have a narrow pore size distribution in the mesopore regions. MgO- template mesoporous carbon is characterized by high percentage of capacitance retention at... 

FIGURE 2.21 Capacitance retention (CCq ), normalized based on the capacitance of the second cycle (Cq), versus cycle number for the ES cells either with (O) or without (A) Ti(IV) in the electrolyte (1 M KCl scan rate = 50 mV s" )- (Reprinted from Electrochemistry Communications, 13, Ataherian, F., and N. L. Wu, 1.2 Volt manganese oxide syimnetric supercapacitor, 1264-1267, Copyright 2011, with permission from Elsevier.)... 

EDLC delivered an average energy and power of 45 and 1.5 kWkg" , respectively, at the operation voltage of 3.6 V and the current density of 1 Ag >. In addition, a capacitance retention of more than 80% was achieved after 50,000 cycles. However, the solnbility of the common conducting salts such as the TEABF4 in the ADN solvent is lower than in the ACN. The ionic conductivity of the ADN-based electrolyte is also much lower than that of the ACN-based electrolytes, which limits the power performance of the ADN-based EDLCs. 

TEABF4 (61.6% capacitance retention vs. 75.5% capacitance retention after 10,000 cycles), which was related to the morphology change of the electrode materials after long cycling tests. 

Souze et al. have fabricated the solid electrolyte-based supercapacitor based on SWCNTs/PANI on polyethylene terephthalate-PET substrates. They have used H2SO4-PVA gel electrolyte and measured the pseudocapacitive properties and estimated the coulometric specific capacitance of 76.7 F cm [87]. The poly (3,4-ethylenedioxypyrrole) and PEDOT wrapped Sb2S3 nanorods were synthesized hydrothermally by Reddy et al. [88] and 1008 F/g specific capacitance, 504 W/kg power density, and 88 % capacitance retention over 1000 cycles were estimated in the fabricated supercapacitor. Further, the supercapacitor was fabricated using semisolid electrolyte using PMMA in ionic liquid. 

Px-MWCNT ratios were maintained as 0.75 0.25 (PANi-75), 0.50 0.50 (PANi-50) and 0.25 0.75 (PANi-25). PANi-50 and PANi-25 nanocomposites based supercapacitors exhibited 91 % and 93 % capacitive retention after 2000 charge-discharge cycle while pure PANi showed only 67 % capacitance retention for the same number of cycles. The diffusion length decreased with a decrease in PANi content in the nanocomposites as shown in Table 1. The enhancement of the charge-discharge rate capability of supercapacitors is attributed to the diffusion length of the nanocomposites [23]. 

There was some interest in making a gel using acrylic acid and its salts. Iwakura et al. reported on an EDLC capacitor using a cross-linked potassium poly(acrylate) hydrogel. ° The capacitance with a polymer electrolyte was 150 F/g, which was a little higher than with the aqueous KOH electrolyte (144 F/g).The effect was attributed to pseudocapacitance owing to the use of the hydrogel in the capacitor cell. Moreover, the capacitance retention after 20000 cycles was found to be 82% of the initial capacitance for the polymer-based electrolyte while it was only 72% for the aqueous KOH electrolyte. 

The capacitance retention of the HMC electrode was also studied by recording charge-discharge profiles for 2000 cycles at 1.0 A and the corresponding data are presented in Figure 4.10b. Despite the initial decrease in capacitance for the first 100 cycles, probably due to the attainment of equilibrium electrode potentials, the HMC has shown very good cycle stability up to 2000 cycles and retains 88% of the initial capacitance. The hollow macroporous core, which is connected and open to the outer mesoporous... 

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