Materials for Rechargeable Batteries, Capacitors

The most widely discussed application of electrically conductive polymers, that can be switched reversibly between two redox states, is their use for the storage of electrical energy in rechargeable batteries. Initial enthusiasm based on optimistic ideas has been quenched by several not fully solvable circumstances such as self-discharge and unsufficient cycle stability [12,13]. A loss of 10% in 1000 cycles for instance is an admirable scientific result, but death for a technical application. 

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]. 

Early publications describe rechargeable batteries made from iodine doped PT combined with zinc or lithium electrodes for the construction of primary and secondary electrochemical cells PT samples has been named to be prepared chemically or -leading to better performances - electrochemically [76-78]. Further studies have confirmed high voltage and good energy density of PT in electrochemical cells, but on the other hand the self-discharging properties as a serious problem for the technical application of this material was also named [79-83]. Battery assemblies with PT as 

An improvement of performance has been obtained with the use of bithiophene as a starting material instead of thiophene for the synthesis of PT. An increase in the specific charge was observed and attributed to the higher regularity in the PT structure [87]. A poly(bithiophene)/lithium solid state cell with poly(ethyleneoxide)/ lithium perchlorate electrolyte was found to have a remarkable stability of 300 cycles at a working temperature of 70°C [88] an initial activation phase was required during cycling, afterwards the coulombic efficiency was 98%. 

Also substituted PTs have been claimed to be useful for application as energy storing materials [89-91] electrochemical studies have shown the relationship between the polymer structure and the electrochemical behavior of these substituted PTs as materials for rechargeable batteries having lower oxidation potentials than unsubstituted PT. 

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