Experimental Analysis of the Scaling Properties of Solid Polymer Electrolytes upon Five Years of Storage: From Fractal Crystallization to Carrier Relaxation

Abstract

The performances of solid-state ambient-temperature batteries over long time periods are found to depend strongly on the crystallization processes of the electrolytes. Some advanced materials displaying stable electrochemical properties were prepared and studied by ac measurements in an attempt to obtain a more precise knowledge of the influence of the crystallization processes of nonhomogeneous media upon the ionic conductivity. The impedance spectra have been fully described and the physical origin of each parameter is emphasized. The results are discussed in terms of an irreversible transfer of the ionic carriers across "bulk interfaces," which may be defined as the storage location of the space charges, or more precisely as the geometrical support of any energetic singularity with respect to any intensive thermodynamic parameter. The bulk dynamic behavior of the ionic carriers in such a l~eterogeneous medium is described by using the fractal geometry concept. The dispersive index ~ is shown to be related to the fractal dimension of the media and is suggested to be connected to its crystallization state. Furthermore, some correlations between the different relaxation processes were described. The aging is found not to alter the intrinsic mobility of the ionic carriers in the amorphous phase and may be considered as a dimensional transition of the geometrical metric of the dissipative domains in the medium, and not only a simple percolation network evolution.