Quinone-based redox flow batteries (RFBs) have comparable performance to all-vanadium RFBs but with reactants composed of earth-abundant elements, and hold promise for safe, cost-effective, large-scale energy storage. One of the major obstacles to their practical implementation is capacity fade during cycling, which is faster than that observed in all-vanadium systems (65-70% capacity retention after 10,000 cycles) [1]. Unlike in all-vanadium RFBs, the crossover of active species across the membrane leads to capacity loss that is not readily recovered with a simple rebalancing method. We present a study of a strategy for alleviating crossover-induced capacity loss, in which the flux of electroactive species across the membrane is balanced by an opposite flux of the same species in the complementary redox state. A model for balanced species flux across the membrane is developed and implemented in a quinone-based battery with a perfluorinated membrane. Its application results in a replenishment of capacity in the capacity-limiting side of the battery and reduces capacity loss to < 0.02%/cycle over hundreds of cycles at the time this abstract is being written. Criteria for extending this approach to other redox flow battery chemistries, and for enabling the use of inexpensive separators will be discussed.

[1] B. Dunn, H. Kamath, and J.-M. Tarascon, Science, 334 (2011).

Figure 1. Computed fluxes of bromine and bromide ions across a Nafion membrane as a function of state-of-charge (SOC). At 50% SOC, fluxes across the membrane are balanced.