A Detailed Investigation into the Electrical Conductivity and Structural Properties of [Poly(ethylene oxide)‐succinonitrile]‐Li(CF₃SO₂)₂N Solid Polymer Electrolytes

Abstract

A solid polymer electrolyte (SPE) was prepared via a solution casting method from a blend of equal weight fractions of poly(ethylene oxide) (PEO) and succinonitrile, used as the polymer matrix, and a salt, Li(CF3SO2)2N (x = 0–0.3 in weight fraction). A plot of the electrical conductivity (σ25°C) vs. x showed an upturned U‐shape, with the highest value being ~3.9 × 10−4 S/cm for x = 0.25 (EO/Li+ = 9.8; the optimum conducting composition). The electrolytes with x ranging from 0.15 to 0.3 showed a linear trend in their log(σT0.5) − (T−To)−1 curves with low pseudo‐activation energy values, suggesting the presence of highly conductive amorphous domains, as confirmed by X‐ray diffractometry measurements, Fourier‐transform infrared (FT‐IR) spectroscopy, polarized optical microscopy, and differential scanning calorimetry studies. The change in PEO chain conformation with x is discussed in detail using FT‐IR spectroscopy in the light of earlier results reported for PEO − Li(CF3SO2)2N SPEs.

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“…This, therefore, offers segmental motion only, which results in a poor electrical conductivity, ~10 −10 S cm −1 at 25 °C . It has already been shown that the PEO‐ionic salt complexation is an easy way to reduce the PEO crystallinity, thereby to improve the electrical conductivity . This is also visible in the σ 25 °C — x curve of the PEO x ‐DST electrolyte.…”

“…The variation of σ 25 °C with x for the PEO x ‐DST electrolyte is a commonly observed phenomenon of the polymer electrolytes, and can be explained using a general equation: σ = nq μ . The notations, n , q , and μ stand for the concentration, charge, and mobility of the free ionic species, respectively.…”

“…The logσ − T −1 study is a simple but effective tool to determine the nature of polymeric chains and level of the easiness of the ion transport . For example, a crystalline or semicrystalline polymer having long linear polymeric chains with slow segmental motion results in a linear logσ − T −1 curve below its melting temperature ( T m ), while, a polymer having a semirandom motion of short polymer segments in the amorphous domains results in a downward logσ − T −1 curve.…”

“…For the synthesis of the PEO x ‐DST solid polymer electrolyte, a mixture of PEO and DST was dissolved in acetonitrile under the string at ~70 °C for 24 h . The homogeneous solution was poured on a Teflon Petri dish, followed by drying at room temperature under nitrogen gas for 2 weeks.…”

“…We have optimized electrical conductivity (σ 25 °C ) of the electrolyte by varying x ‐value from infinity to 8. We have also carried out logσ − T −1 study to determine the nature and the easiness of ion transport in the electrolyte . The variations of σ with x and temperature are explained using the XRD and differential scanning calorimetry (DSC) studies.…”