MODIFICATION OF DARAMIC, MICROPOROUS SEPARATOR, FOR REDOX FLOW BATTERY APPLICATIONS

Methods to incorporate ion-selective properties in a microporous separator (Daramic) to improve its selectivity, were investigated. Adsorption of a polyelectrolyte/ion-exchange resin on the Daramic separator greatly reduced its hydraulic permeability (K(h)) and only a slight decrease in the diffusion coefficient of the membrane was observed. The Daramic with the highest selectivity and an area resistance less than 3 OMEGA-cm2, was obtained by treatment with Amberlite CG400 and further crosslinking using divinyl benzene (DVB). A coulombic efficiency of greater than 90% was achieved during charge/discharge cycling of a vanadium redox test cell using this membrane, compared with about 77% for the original material. This membrane has been tested for over 8000 hours or 1650 cycles in a vanadium redox cell with no sign of deterioration. Long-term exposure to the vanadium (V) solution has also confirmed the excellent stability of the treated membrane for this application.