New solid polymer electrolytes (PEO₂₀–LiTDI–SN) for lithium batteries: structural, thermal and ionic conductivity studies

Solid polymer electrolyte films based on Poly(ethylene oxide) (PEO) have been prepared by solution casting technique using acetonitrile as a solvent. Succinonitrile (SN) was used as a plasticizer and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (LiTDI) as a doping salt. The following techniques such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermo gravimetric analysis, AC-impedance analysis and linear sweep voltametry have been employed to characterize the prepared solid polymer electrolyte films. The crystalline and amorphous nature of polymer electrolytes was confirmed by XRD and DSC analysis respectively. The electrolyte film with 30 wt% of SN was thermally stable up to 260 °C. The ionic conductivities of polymer electrolyte films were calculated from the AC-impedance analysis. The undoped PEO₂₀–LiTDI electrolyte exhibited the ionic conductivity of 9.64 × 10⁻⁷ S cm⁻¹ and this value was increased to 2.83 × 10⁻⁵ S cm⁻¹ when 30 wt% of succinonitrile was added to PEO₂₀–LiTDI electrolyte at 23 °C. The temperature dependent conductivity obeys Arrhenius behavior and the activation energy decreased to 0.264 eV. The electrochemical stability of the optimum conducting composition is 4.3 V, which make it attractive as electrolyte for Li battery.