Nonlinear Ionic Conductivity of Solid Electrolytes and Supercooled Ionic Liquids

Abstract

In this chapter, we present experimental and theoretical results for the nonlinear ionic conductivity of solid electrolytes and of supercooled ionic liquids at large electric fields exceeding 100 kV/cm. The nonlinear conductivity was measured by nonlinear ac impedance spectroscopy, i.e., by applying large ac electric fields and analyzing the measured current density spectra, in particular, higher harmonics in the current density spectra. We first review the first and second Wien effect found in classical strong and weak electrolyte solutions as well as the strong nonlinear ion transport effects observed for inorganic ionic glasses and for polymer electrolytes. Then we present models describing the nonlinear ion conductivity of classical electrolyte solutions, ionic glasses, and polymer electrolytes. Finally, recent results are presented for the nonlinear ionic conductivity and permittivity of supercooled ionic liquids. We show that supercooled ionic liquids exhibit anomalous Wien effects, which are clearly distinct from the classical Wien effects. Some ionic liquids exhibit a very strong nonlinearity of the ionic conductivity, manifesting even in seventh-order harmonic currents. We also discuss the frequency dependence of higher-order conductivity and permittivity spectra of these supercooled liquids.