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Broad Temperature Range Electrolytes Based on Ionic Liquid / Solvent Systems for Electrochemical Double Layer Capacitors
It was found that the ionic conductivity of binary mixtures depends on their composition, and the highest values were obtained for a proportion close to 50%wt in ionic liquid. The addition of organic solvent enhances the conductivity and fluidity of mixtures, especially at low temperature. The ionic conductivity of mixtures reaches 1.9 mS/cm at 223K with a viscosity as low as 70cP.
The ionicity of all six electrolytes was assessed by the Walden plot approach with temperatures rising from 283K to 353K. Thus it was demonstrated that pure ionic liquids and ionic liquids/gamma-butyrolactone mixtures behaviour follows the partial Walden’s rule with α~0.8 and 0.65 respectively.
Thermal and electrochemical behaviours of ionic liquids based electrolytes were studied in mesoporous media composed of single wall carbon nanotubes SWCNT bucky papers. DSC measurement revealed that the addition of gamma-butyrolactone prevents the crystallisation of ionic liquids within the range [183K; 313K] whether the mixtures are inside a mesoporous media or not.
Additionally, electrochemical stability window has been assessed for ionic liquids based electrolytes at 223K, 293K and 373K, on glassy carbon and SWCNT mesoporous bucky paper electrodes. The association of pore size-controlled electrode materials and advanced ionic liquids based electrolytes exhibit promising performances and are under further investigation for applications in electrochemical energy storage devices in severe environment.