Conducting polymers expand or contract when their redox state is changed. This expansion/contraction effect can be separated in an intrinsic part because of changes of the polymer backbone on reduction/oxidation and a part depending on the surrounding electrolyte phase, because of osmotic expansion of the polymer phase. The osmotic effect causes solvent molecules to move into the polymer in a number far in excess of those bound strongly in the solvation shell of the mobile ion, resulting in large volume changes. In this paper, a thermodynamic description of the osmotic expansion is worked out. The model is compared with measurements on PPy(DBS) films. The experiments show that the expansion decreases as the electrolyte concentration is increased. This means that a considerable part of the total expansion is due to the osmotic effect. The osmotic effect should be taken into account when interpreting and designing actuator experiments and when comparing experimental results from different sources.

A soft polymer actuator has been constructed based on the volume change of a conducting polymer. The linear expansion (12 % at a load of 0.5 MPa) is the highest yet reported for a centimeter‐scale conducting polymer actuator. This is achieved by controlling the structure on several length scales: Choice of molecular structure, synthesis from a structured medium, and forming the polymer actuator on a compliant, microstructured gold electrode.

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Lithium trivanadate, LiV3OQ, can be prepared in a finely dispersed form by dehydration of aqueous lithium vanadate gels. Two methods of dehydration, both easily adaptable to large-scale production, are described in this work: freeze drying and spray drying. After heat-treatment of the dried gels (xerogels) to remove loosely bound water they show a high capacity for lithium insertion, approaching four additional lithium per formula unit, and good reversibility as electrode materials for high energy density lithium cells. How the heat-treatment temperature influences the crystal structure is demonstrated as well as the electrochemical properties of the vanadium oxide. InfroductionThe layered trivanadate, LiV3O8, 1 is an interesting alternative to V6013 for use as the positive electrode in secondary lithium cells. The intercalation chemistry of this material was pioneered by Besenhard and Schollhorn, who found it possible to insert lithium ions from a nonaqueous electrolyte2 as well as a number of hydrated cations from aqueous electrolytes.3 Early in the development Nassau and Murphy4 realized that the methods used to prepare the oxide strongly influenced its electrochemical properties. They demonstrated that LiV3O8 prepared in an amorphous, glassy state by rapid quenching from the melt had a higher initial capacity than the crystalline analogue. These findings were, howevei not pursued further in the next decade, where several research groups reported on the use of crystalline LiV3O8 as host material for lithium intercalation.5'7High initial capacities were reported for low-rate discharges, the maximum lithium uptake corresponding to more than three additional Li per formula unit, giving a stoichiometric energy density in excess of 650 Wh/kg.There has been a rather large variation between the values for the maximal lithium uptake from different research groups, but in a structural characterization of lithium inserted Lil+XV3O8, Thackeray et at.'° found that the multiplicity of the sites occupied by lithium in the fully intercalated trivanadate suggests the limiting composition Li5V3O. Recently, Manev et at. have shown how this value can be approached using a specially conditioned LiV3OQThe reported rate capability and cycling properties have, in general, not been satisfactory. Several preparation procedures have been devised to improve the performance of LiV3O8, including control of stoichiometry by rapid cooling,16 more efficient grinding,20 and addition of inert nucleation centers like silica or alumina to the melt.21 The main problem seems to be that on slow cooling, LiV3O3 crystallizes as a very hard and tough material, which is difficult to process into proper electrode structures that can maintain their integrity during deep cycling.In 1990 Pistoia et al.22 reported that fully amorphous L1V3O obtained from a precipitation technique showed significantly higher capacity, better rate capability, and longer cycle life than conventionally made crystalline LiV3O8. In the present paper we describe how an ad...

The properties of polypyrrole (PPy) are to a large extent determined by the condition of synthesis and especially by the counterion incorporated as dopant during synthesis. In this work, PPy doped with different alkyl benzenesulfonates are compared. The polymer films are prepared by constant current oxidation of pyrrole in aqueous solutions containing sodium benzenesulfonates having alkyl chain lengths between 1 and 22 carbon atoms. The doping levels of the polymers are evaluated both electrochemically and by means of a quartz crystal microbalance. The mechanical properties of freestanding films of the materials (tensile strength and Young's modulus) together with the reversible linear elongation between the oxidized and reduced states are determined. A maximum in linear elongation of 4% is found for p-(n-octyl)benzenesulfonate, and the highest electronic conductivity is found for p-(nbutyl)benzenesulfonate.

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Polypyrrole films have been characterized by simultaneous cyclic voltammetry driven force-displacement measurements. The aim was to clarify the role of cations in the electrolyte on the speed of response and on the strain of the film. The strain as a function of actuation frequency was studied in alkali metal chloride aqueous electrolytes. The intention was to test the hypothesis of the division of the inserted H 2 O molecules into categories: a smaller number strongly bound to the cation (corresponding to the inner solvation shell) and a larger number entering the film after the insertion of the cations because of forces related to osmotic pressure difference. The two processes have very different time constants: The solvated H 2 O molecules are associated directly with the cations, and are therefore inserted in a faster process, whereas the second type enters the film much more slowly. At higher frequencies, the strain depends almost exclusively on insertion of strongly solvated cations and therefore depends on the hydration number of the cations: Li + (hydration number~5.4) gives more strain than Na + (~4.4) and much more than Cs + (~0) as predicted by the model.