Volumetric capacitance

Sohd tantalum capacitors have a high volumetric capacitance which makes them attractive for use in miniaturized electronic systems like cellular telephones, hand-held video cameras, and personal computers. The insensitivity of their capacitance to temperature and their abiUty to operate at temperature extremes explains why these devices are used in such harsh environments as automobile engine compartments. Sohd tantalum capacitors are extremely rehable and, therefore, are often the capacitor of choice in critical appHcations like spacecraft electronics, pacemakers, and safety equipment. 

Graphene functionalized with polyaniline can be used as a high-performance flexible electrode. The gravimetric and volumetric capacitances of the hybrid reach 233 F g1 and 135 F cm 3 respectively, more than those of graphene paper (147 Fg-1 and 64 F cm 3) [90],... 

Arulepp et al. [81] reported an in situ technique of CDC activation whereby Ti02 was mixed with TiC and chlorinated. During synthesis, titanium in the Ti02 was etched, leaving controlled amounts of oxygen to etch the carbon. It was shown that the oxidation treatment improved the volumetric capacitance but not the gravimetric capacitance. This was perhaps because of unreacted Ti02 in the sample. The carbon was ideally polarizable at E < 2.8 V and showed a power density of 2.5kW/kg. 

To optimize the device volumetric capacitance density, once the DLC geometric parameters such as the cell size, the electrode thickness, and width have been fixed, the development efforts must be concentrated on the research of the carbon performance. Typical commercial carbons [18] have a capacitance density in the range of 50F/cm3. Their capacitance specific density is in the range of 100 F/g. Among the best-performing carbons available, there are those derived from metal carbide (carbide derived carbon [CDC]) [19,20], They may reach a capacitance density of 130-140F/g. At that point, to avoid confusion, it is worth mentioning the difference between carbon or electrode capacitance and DLC capacitance. The later is exactly four times smaller because of the series connection of two electrodes whose volume is half of the total electrode volume. 

Since for practical purposes a high volumetric capacitance of the electrode is an important requirement, the corresponding data are also given in tab. 2. Unlike the increase... 

Table 23.1 Effect of the pore size on the volumetric capacitance and the internal resistance of capacitors made from two carbons A and B. The pores of carbon B are smaller than those of carbon A (Adapted from Ref. [81].)...

Kunowsky, M., A. Garcia-Gomez, V. Barranco et al. 2014. Dense carbon monoliths for supercapacitors with outstanding volumetric capacitances. Carbon 68 553-562. 

Jung, N., S. Kwon, D. Lee et al. 2013. Synthesis of chemically bonded graphene/carbon nanotube composites and their application in large volumetric capacitance supercapacitors. Advanced Materials 25 6854-6858. 

Kurra, N., N. A. Alhebshi, and H. N. Alshareef. 2014. Microfabricated pseudocapacitors using Ni(OH)2 electrodes exhibit remarkable volumetric capacitance and energy density. Advarwed Energy Materials 4 1401303. 

Skinner B, Chen T, Loth MS, Shklovskii BI (2011) Theory of volumetric capacitance of an electric double-layer supercapacitor. Phys Rev E 83 056102... 

Figure 8.5 Volumetric capacitance of microporous carbons in TEABF4/AN electrolyte vs average width (/. ) of pores accessible to CCI4 [57].

Within the supercapacitor industry, it is widely speculated that stand-alone screen-printed carbon electrodes might one day attain equivalent-series gravimetric capacitances of 100Fg (based on the total mass of carbon, binder, and ion-supplying solution), and equivalent-series volumetric capacitances of... 

Although much work is stiU necessary for determining the exact electrochemical behavior of the individual oxygenated surface functionalities, their contribution in enhancing capacitance of nanoporous carbons in acidic or basic media is a demonstrated fact. However, mie of the drawbacks of most nanoporous carbons is their low density which leads to a low volumetric capacitance and consequently to insufficiently compact supercapacitors. Such disadvantage can be circumvented... 

Activated Carbons, Fig. 4 Correlation between (a) gravimetric capacitance or (b) volumetric capacitance and BET-specific surface area (Sbet) of various activated carbons in 0.5 M (C2H5)4NBF4/propylene carbonate solution [21]. The capacitance was measured by the galvanostatic method (40 mAg 1.7 - 3.7V vs. Li/Li )... 

Zeolite templated carbons exhibit high performance without extensive activation due to the high surface areas and long range orders of their porous structures. Wang et al. [37] used zeolite X (670 m. gr, 1.4 nm pore size) and 8 hr of chemical vapor deposition (CVD) to introduce carbon into the template. The resulting template CNX-2 (2700 m2.g i) had capacitance of 158 Rgy (at 0.25 A.gyi) and energy density of 25 Wh.gyi, respectively, in aqueous electrolyte. Due to the ordered nature of the pore structure, over 97% of the capacitance was retained at rates of 2 A.gyi. The zeolite could produce dense carbon pore structure (1.07 cm. g-i) and improved volumetric capacitance versus most activated carbon materials [37]. 

One noted patent presented by the U.S. Department of Energy (US 6,299,850 Bl) describes an activation method for the carbonization of a pol5dmide or other polymeric material in which an aqueous HNO3 oxidizing agent followed by multiple thermal treatments is used. The resulting activated carbon material possesses a high volumetric capacitance of 300 F/cm. Several commercial firms developed similar proprietary methods in the s)mthesis of activated carbon. 

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