Rheological behavior of gel polymer electrolytes: yield stress and viscoelasticity

In redox flow batteries (RFBs), semi-solid flow cells incorporate solid particles in the same medium than the electrolyte in the form of slurry to increase energy efficiency. However, rheological properties of the fluid hosting the solid particles need to favor particle stability and pumping process within the RFB. In this study, the materials used to formulate a gelled polymer electrolyte (GPE), which will be used as a suspending fluid for dense zinc microparticles in a zinc slurry-air RFB, were analyzed. It was found that when using polyacrylic acid and attapulgite gelling agents together, a yield stress behavior was obtained. This satisfactory result was accomplished even in harsh alkaline conditions (pH > 14), representative of the battery operation conditions in which the chemical stability of gelling agents is threatened. Yield stress values were obtained by fitting experimental data to the Herschel-Bulkley model, and results were compared to those obtained by creep tests. Results indicate that the GPEs presented in this study are good candidates to host zinc microparticles for a zinc slurry-air RFB. Graphical abstract