Marina Mastragostino

Conducting polymers as electrode materials in supercapacitors

Abstract This paper summarizes the performance data of conventional and especially designed thiophene-based conducting polymers for use as positive and negative electrodes in n/p type supercapacitors. Performance data of polymer composite electrodes are also compared with those of high surface area carbon-based composite electrodes. On the basis of capacity, capacitance and electrode charging resistance data, we selected the best electrode materials, and assembled and tested galvanostatic charge–discharge cycles n/p type pMeT-based supercapacitors and hybrid supercapacitors with pMeT as positive electrode active material and activated carbon as negative. The results of this investigation demonstrate that a conventional polymer such as pMeT can be successfully used in the supercapacitor technology when a hybrid configuration is realized; its use is, indeed, a great advantage because the hybrid supercapacitor outperforms the double-layer carbon supercapacitors presently on the market in terms of specific energy and power.

New trends in electrochemical supercapacitors

The present paper compares the performance of an n/p-type polymer supercapacitor based on n- and p-doped poly(3-methylthiophene) (pMeT) and of a hybrid supercapacitor, based on p-doped pMeT as positive electrode and activated carbon as negative, with that of a double-layer activated carbon supercapacitor (DLCSs), which is representative of the current state of supercapacitor technology. The data on the n/p-type supercapacitor demonstrate that this device is not fully competitive with the DLCSs because of its lower discharge capacity, although all the charge is delivered at high potentials and this makes it suitable for high-voltage applications. The data on the hybrid supercapacitor demonstrate that this device outperforms DLCSs, delivering higher average and maximum specific powers and significantly higher specific energy in the potential region above 1.0 V.

Polymer-based supercapacitors

The use of electronically conducting polymers (ECPs) as pseudocapacitive electrode materials in high-power supercapacitors is a challenge to overcome the performance of carbon-based double-layer supercapacitors for applications requiring high power levels. ECPs provide different supercapacitor configurations but devices with the polymer n-doped form as the negative electrode and the p-doped form as the positive one are the most promising in term of energy and power. This type of supercapacitor has indeed a high operating voltage, it is able to deliver all the doping charge and it has in the charged state both electrodes in the conducting (p- and n-doped) states. Data for poly(3-methylthiophene) positive and negative electrodes, envisioned for a n/p-type supercapacitor, as well as data for cyclability of supercapacitors with composite electrodes based on such conventional polymer are here reported and discussed. The capacitance and cycling stability of poly(3-methylthiophene) are sufficiently high to take this polymer into consideration for supercapacitor technology.

Carbon-Poly(3-methylthiophene) Hybrid Supercapacitors

The challenge to the use of electronically conducting polymers as electrode active materials in supercapacitors is to outperform high-power, double-layer carbon supercapacitors (DLCSs). The present study demonstrates that a hybrid supercapacitor with p-doped poly(3-methylthiophene) (pMeT) as the positive electrode and an activated carbon as the negative electrode outperforms the specific power of the DLCSs without reduction in specific energy while maintaining good performance cyclability over 10,000 cycles. Impedance spectra and cyclability data of galvanostatic charge-discharge cycles of C//pMeT hybrid supercapacitors are presented and discussed.

Electrochemical properties of polyethylene oxide-Li[(CF{sub 3}SO{sub 2}){sub 2}N]-gamma-LiAlO{sub 2} composite polymer electrolytes

The electrochemical properties of polymer electrolytes based on polyethylene oxide (PEO) and Li[(Cr{sub 3}SO{sub 2}){sub 2}N], with and without the addition of dispersed {gamma}-LiAlO{sub 2} powder, are reported. The results clearly indicate that the use of the {gamma}-LiAlO{sub 2} ceramic filler combined with the Li[(CR{sub 3}SO{sub 2}){sub 2}N] salt greatly reduces the crystallization rate and enhances the lithium/electrolyte interface stability.

Composite Polymer Electrolytes with Improved Lithium Metal Electrode Interfacial Properties I. Elechtrochemical Properties of Dry PEO‐LiX Systems

Several types of lithium ion conducting polymer electrolytes have been synthesized by hot-pressing homogeneous mixtures of the components, namely, poly(ethylene oxide) (PEO) as the polymer matrix, lithium trifluoromethane sulfonate (LiCF{sub 3}SO{sub 3}), and lithium tetrafluoroborate (LiBF{sub 4}), respectively, as the lithium salt, and lithium gamma-aluminate {gamma}-LiAlO{sub 2}, as a ceramic filler. This preparation procedure avoids any step including liquids so that plasticizer-free, composite polymer electrolytes can be obtained. These electrolyte have enhanced electrochemical properties, such as an ionic conductivity of the order of 10{sup {minus}4} S/cm at 80--90 C and an anodic breakdown voltage higher than 4 V vs. Li. In addition, and most importantly, the combination of the dry feature of the synthesis procedure with the dispersion of the ceramic powder, concurs to provide these composite electrolytes with an exceptionally high stability with the lithium metal electrode. In fact, this electrode cycles in these dry polymer electrolytes with a very high efficiency, i.e., approaching 99%. This in turn suggests the suitability of the electrolytes for the fabrication of improved rechargeable lithium polymer batteries.

Activated Carbon/Conducting Polymer Hybrid Supercapacitors

This paper presents the work carried out within a European Union (EU) project which led to the development of 3 V and 1.5 kF preseries supercapacitor modules and 2 kW stacks based on hybrid cells with poly(3-methylthiophene) as positive electrode and activated carbon as the negative electrode with propylene carhonate-tetraethylammonium tetrafluoroborate electrolyte. These prototypes, which display a concept of hybrid cell operating with a high-surface-area activated carbon and a conventional electronically conducting polymer, both commercially available, and with a nontoxic and nonvolatile electrolyte, provide a successful response to the market demand for high power and energy supercapacitors operating with an environmentally friendly electrolyte.

Impedance analysis of electronically conducting polymers

Abstract We discuss in detail the equivalent circuits used to model the impedance of electronically conducting polymer systems and the procedure for the impedance analysis of these systems to account for deviation from the ideal behaviour. Impedance spectra of pyrrole-based and thiophene-based polymers of different thickness and at different values of injected charge in cells with liquid electrolytes and solid polymer electrolytes are reported, and the electrochemical parameters are evaluated and discussed.

Electrochemical characterization of “n” doped polyheterocyclic conducting polymers—I. Polybithiophene

Abstract The electrochemical behaviour of “n” doped poly 2-2′ bithiophene (pBT) was characterized in acetonitrile with 0.2 M tetrabutylammoniumfluophosphate and the results were compared with those of the “p” doping—undoping process. Electrochemical characterization of pBT was carried out in other solvents with tetrabutylammonium, potassium and lithium salts. The results showed that pBT “n” doping is strongly dependent both on the solvents properties and on counterion size. While “n” doping of pBT proved impossible in some solvents with lithium salts, it was successful when the effective radius of the lithium ion was increased by using hexamethylphosphoramide, a solvent with high solvating power.

Polymer Selection and Cell Design for Electric‐Vehicle Supercapacitors

Supercapacitors are devices for applications requiring high operating power levels, such as secondary power sources in electric vehicles (EVs) to provide peak power for acceleration and hill climbing. While electronically conducting polymers yield different redox supercapacitor configurations, devices with the n-doped polymer as the negative electrode and the p-doped polymer as the positive one are the most promising for EV applications. Indeed, this type of supercapacitor has a high operating potential, is able to deliver all the doping charge and, when charged, has both electrodes in the conducting (p- and n-doped) states. This study reports selection criteria for polymer materials and cell design for high performance EV supercapacitors and experimental results of selected polymer materials.