Asymmetric hybrid capacitor

Salinas-Torres, D., J. M. Sieben, D. Lozano-Castell6, D. Cazorla-Amoros, and E. Morallon. 2013. Asymmetric hybrid capacitors based on activated carbon and activated carbon fibre-PANl electrodes. Electrochimica Acta 89 326-333. 

The third and the most important approach to meet the goal that is under serious investigation is to develop asymmetric (hybrid) capacitors. As shown in Fig. 4.3 various hybrid capacitor systems are possible by coupling redox-active materials (e.g., graphite [10, 31], metal oxides [5, 14], conducting polymers [17,18]), and an activated carbon (AC). There are suggested two different systems, one is aqueous and the other is non-aqueous. Some of them are listed below in Fig. 4.4. These approaches can overcome the energy density limitation of the... 

In order to avoid the problems associated with the instability of the n-doping process of the polymer, it has been proposed to replace the n-doped polymer at the negative electrode with a carbon electrode to form the so-called hybrid capacitor [22, 33, 40]. Such hybrid capacitors with a p-doped polythiophene derivative as the positive electrode and activated carbon as the negative electrode were found to outperform double-layer carbon capacitors in terms of specific power while maintaining good performance cyclability over 10000 cycles [40]. Another asymmetric hybrid capacitor has been built using a lithium titanate (Li4Ti50i2) intercalation anode, instead of a carbon electrode and PFPT electrode [35]. 

The third and the most important approach to meet the goal that is under serious investigation is to develop asymmetric (hybrid) capacitors. 

The ESs mentioned above consist of two electrodes with the same type of capacitive materials made from either EDL capacitive materials or pseudocapacitive materials (symmetrical configuration). In order to further increase the operating potential window, energy, and power density, a new type of ES has been developed, which is known as hybrid capacitors. With extensive achievements in this area, various types of hybrid ESs have been developed. Generally, hybrid capacitors utilize both the EDL capacitance and faradaic reaction to store charges. The hybrid capacitors reviewed in this book include (1) ESs based on composite electrodes made from both EDL capacitive materials and pseudocapacitive materials (2) asymmetric ESs with one EDL electrode and another pseudocapacitive or battery-type electrode and (3) asymmetric ESs with one pseudocapacitive electrode and another rechargeable battery-type electrode. 

Deng, L. J., Z. P. Hao, J. F. Wang et al. 2013. Preparation and capacitance of graphene/ multiwall carbon nanotubes/Mn02 hybrid material for high-performance asymmetrical electrochemical capacitor. Electrochimica Acta 89 191-198. 

Lekitima, J. N., K. I. Ozoemena, C. J. Jafta et al. 2013. High-performance aqueous asymmetric electrochemical capacitors based on graphene oxide/cobalt((II))-tetrapyrazinoporphyrazine hybrids. Journal of Materials Chemistry A 1 2821-2826. 

Finely dispersed carbon substances introduced into the active mass of pseudocapacitive electrodes of hybrid (asymmetric) capacitors play the most important role in operation of an efficient volumetric collector. 

Electrodes of various types are used in hybrid (asymmetric) supercapacitors (HSCs). For example, one of the electrodes is highly dispersed carbon, that is, a double-layer electrode, and the other electrode is a battery one or one of the electrodes is carbon and the other one is a pseudocapacitor, for example, based on electron-conducting polymer (ECP). The main advantage of HSCs as compared EDLCs is an increase in energy density because of the wider potential window. The main fault of HSCs, meanwhile, as compared to electric double-layer capacitors (EDLCs), is a decrease in cyclability following the limitations posed by the nondouble-layer electrode. 

Axion Power International Inc. has developed a PbC capacitor battery, as shown in Figure 1.34. The full technical description of Axion s proprietary PbC technology is a multi-celled asymmetrically supercapacitive lead-acid-carbon hybrid battery. Like a lead-acid battery, the PbC battery consists of a series of cells. Within the individual cells, however, the construction is more complex. Whereas the negative electrodes in lead-acid batteries are simple sponge lead plates, the negative electrodes in a PbC battery are five-layer assemblies that consist of a carbon electrode, a corrosion barrier, a current collector, a second corrosion barrier, and a second carbon electrode. These electrode assemblies are then sandwiched together with conventional separators and positive electrodes to make the PbC battery, which is filled with an acid electrolyte, sealed and connected in series to the other cells [11]. 

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