J.F. Le Nest

Poly(dimethylsiloxane)-poly(ethylene oxide) based polyurethane networks used as electrolytes in lithium electrochemical solid state batteries

Abstract Ionic conductivity and redox stability domain of a new type of polymer electrolyte have been studied. The polymer electrolytes were prepared from a network of poly (dimethylsiloxane-grafted ethylene oxide) copolymer crosslinked by an aliphatic isocyanate (grafted PDMS) and containing 10 wt% LiClO 4 . Ionic conductivities higher than 10 −5 ω −1 cm −1 are obtained above 30°C. The study of the electrochemical stability of the crosslinking agent suggests that the unreacted isocyanate groups are not stable. The electroactivity domain of the grafted PDMS-LiClO 4 10 wt% electrolyte is larger than 3 V. The performances of a solid state battery using this electrolyte have been investigated. The first discharge and charge depths were 73%. The rechargeability behaviour have been compared with those of a Li/RuO 2 battery with a linear high molecular weight P(EO) 8 -LiClO 4 as electrolyte.

A new polymer network for ionic conduction

Novel polyether networks based on polyethylene oxide triols and polyethylene oxide diisocyanates were prepared and characterized. Their glass-transition temperatures, dynamic mechanical properties and ionic conductivities were assessed both without any added salt and with increasing concentrations of LiClO4 and LiN(CF3SO2)2. Both the more disordered topology of the network and the plasticizing character of the imide-type anion contribute to enhance the conductivity.

Cationic transport numbers in polyether-based networks containing lithium salts

Abstract Measurements of the Li + transport number by the Tubandt method on solid electrolytes based on polyethers crosslinked with triisocyanates containing various lithium salts gave values consistently indicating the predominance of anionic conduction. Transport numbers ( t + ) were found to be temperature independent between 70 and 120 °C, but to decrease as the salt concentration increased. The other parameters studied were the nature of the anion and the structure and length of the polyether segments.

Polymer electrolytes based on modified polysaccharides. 2. Polyether-modified cellulosics

In order to improve the film-forming properties of polyether-based polymer electrolytes a new family of materials was synthesized. The structures described in this work involve a cellulosic ether backbone on which oligoethers were grafted and crosslinked in various proportions via urethane chemistry and to which lithium perchlorate was subsequently added as a source of ionic species. The resulting networks were fully characterized in terms of glass transition temperature, dynamic mechanical properties and ionic conductivity. With respect to the optimized polyether-based networks studied previously, the introduction of polysaccharide chains does not alter the basic features neither qualitatively nor quantitatively.

Mechanism of high ionic conductivity in elastomeric networks

Abstract The viscoelastic properties and the ionic conductivity of polyether-polyurethane networks containing alkali metal salts have been studied at various temperatures, salt concentrations and network structures. The reduced temperature, TT g , is the predominant parameter which governs the viscoelastic behaviour and the ionic conductivity of these networks. Using the free volume concept an expresssion is derived for the ionic conductivity, irrespective of the macrostructure involved. The logarithm of the reduced conductivity, σ T /σ T R (which is the ratio of the conductivity at a given temperature to that at the reference temperature), is a linear function of the shift factor, log a T , given by the dynamic mechanical properties. A comparison is made between the WLF parameters C 1 and C 2 , obtained from conductivity and viscoelastic measurements.

Mechanism of ionic conduction in polyether-polyurethane networks containing lithium perchlorate

The swelling behaviour of polyethylene oxide-urethane networks (with and without LiClO4) was studied with several organic liquids and water. All the results are consistent with a model for the network-salt interaction involving the solvation of Li+ ions by oxygen atoms of the ether. More specifically, strong interactions take place between ionic quadrupoles and two polyether chains leading to reversible physicochemical (ionic) crosslinks. The number of such interactions grows with salt concentration up to a limit characterised by one ionic crosslink every twelve ethylene oxide units. An ionic transport mechanism (conduction) is proposed on the basis of this model considered in a dynamic context.

A mechanism of ionic conduction in cross-linked polyethers

Abstract A wide variety of polyether-based networks were prepared and tested in terms of ionic conductivity as a function of the type and concentration of the salt added, the structure of the reticulate and the temperature. This study includes ionomeric networks. The results indicate the occurrence of polyether chain partitioning by the dissociated salt and formation of quadrupoles binding two such chains. A model is proposed to rationalize the conduction mechanism on the basis of the overall experimental evidence.