Synergistic effects of binary lithium salts on ion transport and dielectric relaxation in poly(methyl methacrylate) grafted natural rubber solid polymer electrolytes

Abstract

A series of solid polymer electrolyte films were prepared using a casting solution with a polymer matrix comprising 49% poly(methyl methacrylate)-grafted natural rubber (MG49). These films incorporated binary lithium salts: lithium tetrafluoroborate (LiBF 4 ) combined with either lithium trifluoromethanesulfonate (LiTf) or lithium iodide (LiI). These films ' dielectric properties and ion association behavior were examined using potentiostatic electrochemical impedance spectroscopy (EIS) and Fourier transform infrared (FTIR) deconvolution. The key findings demonstrated that the increase in both the dielectric constant ( epsilon r ) and dielectric loss ( epsilon i ) was significantly correlated with enhanced ionic conductivity, reaching a value of 1.89 x 10-6 S cm- 1 , which was attributed to enhanced ionic and segmental mobility. A peak observed in the M i versus frequency plot confirmed the ionic conductor behavior. The (30:70) ratio of LiBF 4 to LiI exhibited the highest performance, with superior ionic conductivity, dielectric behavior, tangent loss, number of charge carriers, mobility, and diffusion coefficient, surpassing the performance of the single salt or LiBF 4 to LiTf. This indicates that the combination of LiBF 4 and LiI is particularly effective for applications requiring improved dielectric properties.