Effect of ethylene carbonate in poly (methyl methacrylate)-lithium tetraborate based polymer electrolytes

Thin films composed of poly (methyl methacrylate) (PMMA), lithium tetraborate (Li2B4O7) and ethylene carbonate (EC) were prepared by solution casting method. The highest ionic conductivity at room temperature was achieved for the composition PMMA:Li2B4O7:EC (42:18:40) with the value 1.29 × 10−5 S cm−1. The presence of plasticizer in the polymer complex is crucial in improving the ionic conductivity by increasing the concentration of free mobile ions through the structural conversion from crystalline to amorphous phase. This conversion lowers the viscosity of the polymer complex. Conductivity–temperature plots were found to obey Williams–Landel–Ferry (WLF) mechanism. Dielectric data was analyzed using the dielectric permittivity (ε′) and dielectric modulus (M′) of the samples. Fourier transform infrared (FTIR) studies confirmed that complexation occurs between PMMA, Li2B4O7 and EC. Thermal stability of the polymer complex, which decreases with the addition of plasticizer (EC), was determined using thermal gravimetric analysis (TGA).

Research Highlights
► PMMA: Li2B4O7: EC (42:18:40) shows the highest ionic conductivity.
► The conversion from crystalline to amorphous phase lowers the viscosity.
► Addition of plasticizer decreases the thermal stability.