Non-aqueous redox flow batteries (NRFBs) have the potential to surpass current aqueous redox flow batteries for grid energy storage through wider electrochemical stability windows and selection of redox couples. However, the high cost of ion exchange membranes (IEMs) as battery separators remains one of the major challenges to make NRFBs commercially feasible. We utilized relatively inexpensive, commercial off-the-shelf (COTS) porous separators in place of IEMs and redox-active polymers (RAPs) as our electrolyte in non-aqueous solvents. Due to typically low solubility of polymers, this is the first case of RAP electrolyte utilized for redox flow batteries, greater than 2.0 M in acetonitrile. Transport experiments were performed using RAPs to analyze the crossover of RAPs through COTS separators and to elucidate size-based selectivity of charge balancing ions over RAPs through COTS separators. Our results showed that increasing molecular weight of RAPs led to a low amount of RAP crossover through COTS separators. We also observed greater selectivity (~70) of charge balancing ions to RAPs through COTS separators due to increase of molecular weight. The selectivity of charge balancing ions over electrolytes in this system was greater than those reported in aqueous redox flow batteries utilizing IEMs.

Redox active polymers for size-exclusion transport in nonaqueous redox flow batteries

249th National Meeting (2015)

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