A High-Current, Stable Nonaqueous Organic Redox Flow Battery

Abstract

Nonaqueous redox flow batteries are promising in pursuit of high energy density storage systems owing to the broad voltage windows (>2 V) but currently are facing key challenges such as limited cyclability and rate performance. To address these technical hurdles, here we report the nonaqueous organic flow battery chemistry based on N-methylphthalimide anolyte and 2,5-di-tert-butyl-1-methoxy-4-[2′-methoxyethoxy]­benzene catholyte, which harvests a theoretical cell voltage of 2.30 V. The redox flow chemistry exhibits excellent cycling stability under both cyclic voltammetry and flow cell tests upon repeated cycling. A series of Daramic and Celgard porous separators are evaluated in this organic flow battery, which enable the cells to be operated at greatly improved current densities as high as 50 mA cm–2 compared to those of other nonaqueous flow systems. The stable cyclability and high-current operations of the organic flow battery system represent significant progress in the development of promising nonaqueous flow batteries.

Towards Low Resistance Nonaqueous Redox Flow Batteries

“…The implementation of the MeCN-based electrolyte and Celgard 2500 separator is critical in achieving low ASR, but the Celgard 2500 separator is impractical for a NAqRFB device since it offers no selectivity for small redox active molecules. Implementing Celgard 2500 in full flow cell would require mixed active species electrolytes, 21,23,41,83 which would be cost prohibitive, 7,12,23,41 or emerging large polymeric active species, [55][56][57] which may yield high viscosity electrolytes with poor mass transfer characteristics. 84 Additionally, the highly soluble Fc1N112 +/2+ model active species and low viscosity MeCN-based electrolyte facilitates small mass transfer resistances.…”

“…[20][21][22][23][24][25][26] Even fewer studies have incorporated advanced flow cell designs to minimize area specific resistance (ASR) and increase area specific power density.…”

Uncovering the role of flow rate in redox-active polymer flow batteries: simulation of reaction distributions with simultaneous mixing in tanks

“…Such systems can be cheaper and safer, but the electrochemical stability window of aqueous based electrolytes impedes achievement of high energy density. On the other hand, nonaqueous redox flow batteries (NAqRFBs) provide a wider electrochemical stability window (hence high energy density) [12][13][14][15], while NAqRFBs tend to have lower ionic conductivity and higher electrolyte costs as compared to their aqueous counterparts [16].…”

“Wine-Dark Sea” in an Organic Flow Battery: Storing Negative Charge in 2,1,3-Benzothiadiazole Radicals Leads to Improved Cyclability

“…Mixed-reactant electrolytes with a 1:1 molar ratio of BzNSN and DBMMB were used to decrease redox materials crossover. [38][39] Figure 3a 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 Increasing the redox materials concentrations to a more relevant level, e.g. 0.5 M, encounters challenging situations for good cycling, such as greatly increased electrolyte viscosity and redox materials crossover.…”

“…As shown in Figure 3b 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 addition, even more stable cycling with almost no capacity fading for 40 cycles was obtained in a flow cell containing 0.3 M ROMs in 1,2-dimethoxyethane (DME) ( Figure S9 in the Supporting Information), as DME is generally more stable towards organic radical anions 32,39 . So far, the high-concentration cell efficiency and stability are among the best flow cell performance achieved in nonaqueous flow batteries, although further improvement is still needed to make this system practically attractive.…”