Electrochemical Investigations of Polyethylene Glycol-Based "Soggy Sand" Electrolytes - From the Local Mechanism to the Overall Conduction

Using the example of SiO2 dispersions in LiClO4/polyethylene glycol electrolytes, the conduction mechanism of "soggy sand" electrolytes is discussed. The study is essentially based on zeta potential, impedance and transference number measurements as well as on modeling. All the results can be explained by anion adsorption by the oxide particles and increased concentration of free Li+ in the double layer. The initially colloidal dispersion quickly forms fractal networks by cluster-cluster aggregation. Once they percolate, an interfacially dominated Li+ conductance is observed. The subsequent coarsening of the network is self-decelerating leading to a steady state conductivity that is, for low volume fractions, enhanced compared to SiO2 free electrolytes. At higher values, blocking and inhomogeneity effects (e. g., salt trapping) lead to decreased values of the overall conductivity.