Effect of storage time on the ionic conductivity of chitosan-solid polymer electrolytes incorporating cyano-based ionic liquids

Four solid polymer electrolytes (SPEs) of chitosan-based host matrix were prepared by solvent casting method. The SPEs incorporated 1-ethyl-3-methylimidazolium thiocyanate ([C2mim][SCN]), 1-ethyl-3-methylimidazolium dicyanamide ([C2mim][N(CN)2]), 1-ethyl-3-methylimidazolium tricyanomethanide ([C2mim][C(CN)3]), and 1-butyl-3-methylimidazolium thiocyanate ([C4mim][SCN]). The structure, morphology, thermal behavior, and electrochemical properties of the synthesized free-standing transparent membranes were studied. It was verified that all the samples are amorphous and thermally stable. TGA of chitosan[C2mim][N(CN)2] membrane showed a Tonset of ca. 100 °C (232 °C) higher than the Tonset of the chitosan matrix (135 °C), highlighting the ionic liquids (ILs) stabilizing effect on the polymer host. The highest ionic conductivity was exhibited by chitosan[C2mim][SCN] with 1.61 × 10-3 S cm-1 at 25 °C and 1.28 × 10-2 S cm-1 at 100 °C. Two years later these ionic conductivity values were still very high (>10-4 S cm-1) and adequate for application in solid-state electrochemical devices (ECDs). Such results attest to the samples long shelf-life, proving that these chitosan[Cnmim][X(CN)m] SPEs are time stable, and thus may easily find practical applications.

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