Polypyrrole batteries

Prototypes of lithium/polypyrrole batteries are under study in various laboratories and low rate, small size versions of these batteries have reached an advanced development stage in European (Munstedt et al, 1987) and Japanese (Sakai et al, 1986) industrial laboratories. 

A polypyrrole-electrolyte-polypyrrole battery has been described 611) but the n-doped polypyrrole is unstable. This can be avoided by using a polypyrrole-polyanion anode, where the charge and discharge depend upon small cations moving into and out of the electrode612). A polythiophene-polythiophene battery has also been described 135). Polyaniline has been studied as a potential battery cathode, for use with an aqueous electrolyte 613,6I4). 

The doping limit of polypyrrole in Li/polypyrrole batteries was investigated by many researchers and charge-discharge coulombic efficiency of almost 100% was obtained up to 20-30% doping (per monomer unit) [36]. 

The facile redox reaction of the conducting polymers and their lightness make them promising candidates for battery electrodes. In addition, they are relatively inexpensive. These considerations prompted considerable theoretical and experimental work on polyaniline and polypyrrole batteries [71-73]. In fact, the pilot studies progressed to a level at which Seiko and Hitachi of Japan were able to put rechargeable polymer-Li batteries on the market [74]. 

A polypyrrole battery has been developed and tested by BASF and VARTA Baterie AG. The positive electrode consisted of electrochemically synthesized polypyrrole doped with tetrafluoroborate. When PPy is used with a lithium counterelectrode at a cell voltage of 3.5 V, a thoretical energy density of 360 W h/kg is estimated for the PPy electrode, although in a practical cell the density is lower [428 30],... 

In a 1997 review, electrochemically active polymers - including also PT - for rechargeable batteries are given [71]. In this review the first two really produced batteries containing polymeric materials are described intensively with their special problems [72] (i) the German Li/polypyrrole battery (Varta-BASF battery) [73-75] and (ii) the Japanese Li/polyaniline battery [75]. 

T. Osaka, K. Naoi, S. Ogano, S. Nakamura, Dependence of film thickness on electrochemical kinetics of polypyrrole and on properties of lithium/polypyrrole battery, J. Electrochem. Soc., 1987,134, pp. 2096-2102. 

Polypyrrole, poly thiophene, polyfuran, polycarbazole, polystyrene with tetrathi-afulvalene substituents, polyethylene with carbazole substituents, and poly-oxyphenazine as electrochemically active polymers for rechargeable batteries 97CRV207. 

Sodium dodecyl sulfate has been used to modify polypyrrole film electrodes. Electrodes synthesized in the presence of sodium dodecyl sulfate have improved redox processes which are faster and more reversible than those prepared without this surfactant. The electrochemical behavior of these electrodes was investigated by cyclic voltametry and frequence response analysis. The electrodes used in lithium/organic electrolyte batteries show improved performance [195]. 

Polyacetylene proved qnite incapable of working in a realistic battery context, and MacDiarmid did not mention this application in his Nobel lectnre of October, 8 2000. However, other materials have proven their worth, and prototype batteries made with polypyrrole and polyaniline as cathodes (positives), and metal or lithiated carbon materials as anodes (negatives), have been demonstrated in dne conrse by the Japanese and German indnstry, for instance. Novdk et al. (1997) have reviewed the field in detail. 

The concept of electrochemical intercalation/insertion of guest ions into the host material is further used in connection with redox processes in electronically conductive polymers (polyacetylene, polypyrrole, etc., see below). The product of the electrochemical insertion reaction should also be an electrical conductor. The latter condition is sometimes by-passed, in systems where the non-conducting host material (e.g. fluorographite) is finely mixed with a conductive binder. All the mentioned host materials (graphite, oxides, sulphides, polymers, fluorographite) are studied as prospective cathodic materials for Li batteries. 

Nitration of the surface of polypyrrole and the subsequent reduction of the nitrate groups has been reported [244] and Bidan et al. [306, 307] have investigated the electrochemistry of a number of polymers based on pyrroles with /V-substituents which are themselves electrochemically active. Polypyrrole has also been successfully deposited onto polymeric films of ruthenium complexes [387], and has been used as an electrode for the deposition and stripping of mercury [388], As with most conducting polymers, several papers have also appeared on the use of polypyrrole in battery systems (e.g. [327, 389] and Ref. therein). 

Many industrial and academic laboratories have investigated doped polymers as improved positive electrodes in rechargeable lithium batteries. A common example is the battery formed by a lithium anode, a liquid organic electrolyte (e.g. LiC104-PC solution) and a polypyrrole film... 

However, some of the basic problems of polypyrrole and of the other heterocyclic polymers act to limit the performance of the lithium/polymer battery, and thus its wide applicability. These are essentially slow kinetics, self-discharge and low energy content. 

Although the diffusion of the counterion is faster in polypyrrole than in polyacetylene, its value is still low enough to influence the rate of the electrochemical charge and discharge processes of lithium/polymer batteries. Indeed the current output of these batteries is generally confined to a few mA cm . Possibly, improvements in the electrode kinetics, and thus in the battery rates, may be obtained by the replacement of standard ... 

Another problem still to be solved in polymer batteries is the self-discharge of the polymer electrode in common electrolyte media. Effectively, the majority of the polymer electrodes show a poor charge retention in organic electrolytes. In situ spectroscopic measurements (Scrosati et al., 1987) have clearly demonstrated the occurrence of spontaneous undoping processes. A typical example is illustrated in Fig. 9.17 which is related to the change of the absorbance of doped polypyrrole upon contact with the electrolyte. 

Fig. 9.16 Cyclic behaviour of lithium batteries using standard pPy(C104) polypyrrole electrodes and modified pPy(DS) electrodes.

The majority of polymer electrodes cannot be doped to very high levels. For instance, polypyrrole may reach doping levels of the order of 33%. This inherent limitation combined with the fact that the operation of the lithium/polymer battery requires an excess of electrolyte (to ensure... 

The benefit of a hybrid phase for the intercalation-deintercalation of mobile species such as Li+ cations is well illustrated by the study of conductive polymers such as polyaniline or polypyrrole intercalated into a V2O5 framework as potential electrode materials in lithium batteries [34]. For PANI/V2O5, an oxidative post-treatment performed under an oxygen atmosphere allowed the authors to compare the conductivity attributed to the polymer, as in absence of reduced cations, there was no electronic hopping between ions, and the conductive state was due only to the... 

Recently supercapacitors are attracting much attention as new power sources complementary to secondary batteries. The term supercapacitors is used for both electrochemical double-layer capacitors (EDLCs) and pseudocapacitors. The EDLCs are based on the double-layer capacitance at carbon electrodes of high specific areas, while the pseudocapacitors are based on the pseudocapacitance of the films of redox oxides (Ru02, Ir02, etc.) or redox polymers (polypyrrole, polythiophene, etc.). 

The molecular orbital (MO) calculations within the PM3 method, using a MOP AC package, provided an explanation of the advantages of a new redox system, poly(l,4-phenylene-l,2,4-dithiazolium-3, 5 -yl) (PPDTA), as a cathode material for high-capacity lithium secondary batteries in comparison with three typical polymer conductors (poly-/>-phenylene, polypyrrole, and polythiophene). The MO calculation revealed that the S-S bond in the 1,2,4-dithiazo-lium moiety of PPDTA caused gap narrowing and a downshift of HOMO and LUMO levels, which is consistent with the electrochemical experiment (HOMO = highest occupied molecular orbital LUMO = lowest unoccupied molecular orbital) <2001MI2305>. 

Kuwabata S, Kishimoto A, Tanaka T, Yoneyama H. Electrochemical synthesis of composite films of manganese dioxide and polypyrrole and their properties as an active material in lithium secondary batteries. J Electrochem Soc 1994 141 10-15. 

Work with PPy and PAni has reached the industrial stage. Bridgestone-Seiko has been selling coin-shaped 3-V polyaniline-based batteries for 5 years (1987-1992), and polypyrrole-based batteries were developed by Varta/BASF in the same period. Such batteries have lower energy densities than those of conventional batteries, but they are superior in terms of selfdischarge. The main characteristics of a typical PAni battery are compared to those of lead and Cd-Ni batteries in Table 4. The values mentioned for energy density and electric capacity density refer to the active material alone. 

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