Broadband dielectric spectroscopy of BMPTFSI ionic liquid doped solid-state polymer electrolytes: Coupled ion transport and dielectric relaxation mechanism

Abstract

Broadband dielectric spectroscopy has been used to explore the charge carrier transport and relaxation mechanisms in different compositions of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide doped poly(methylmethacrylate)-lithium bis(trifluoromethylsulfonyl)imide based solid polymer electrolytes. The free ion diffusivity and number density, which are directly linked with ion transport in ionic liquid based polymer electrolytes, are analyzed following the model of electrode polarization proposed by Macdonald–Trukhan. We have analyzed broadband dielectric spectra in terms of complex electric modulus formalism using two theoretical approaches such as Havrilliak–Negami and Kohlrausch–Williams–Watts functions. It has been observed that charge carrier diffusivity and dielectric relaxation time are strongly temperature dependent, following Vogel–Tammann–Fulcher behavior. It is also evident from the values of stretched exponent β that the relaxation behavior is highly non-exponential in these ionic liquid doped polymer electrolytes.