Evolutionary Design of Low Molecular Weight Organic Anolyte Materials for Applications in Nonaqueous Redox Flow Batteries

Abstract

The integration of renewable energy sources into the electric grid requires low-cost energy storage systems that mediate the variable and intermittent flux of energy associated with most renewables. Nonaqueous redox-flow batteries have emerged as a promising technology for grid-scale energy storage applications. Because the cost of the system scales with mass, the electroactive materials must have a low equivalent weight (ideally 150 g/(mol·e(-)) or less), and must function with low molecular weight supporting electrolytes such as LiBF4. However, soluble anolyte materials that undergo reversible redox processes in the presence of Li-ion supports are rare. We report the evolutionary design of a series of pyridine-based anolyte materials that exhibit up to two reversible redox couples at low potentials in the presence of Li-ion supporting electrolytes. A combination of cyclic voltammetry of anolyte candidates and independent synthesis of their corresponding charged-states was performed to rapidly screen for the most promising candidates. Results of this workflow provided evidence for possible decomposition pathways of first-generation materials and guided synthetic modifications to improve the stability of anolyte materials under the targeted conditions. This iterative process led to the identification of a promising anolyte material, N-methyl 4-acetylpyridinium tetrafluoroborate. This compound is soluble in nonaqueous solvents, is prepared in a single synthetic step, has a low equivalent weight of 111 g/(mol·e(-)), and undergoes two reversible 1e(-) reductions in the presence of LiBF4 to form reduced products that are stable over days in solution.

A Membrane‐Free Redox Flow Battery with Two Immiscible Redox Electrolytes

“…This is substantially less than 150 g/(mol e À ) proposed by Sandford and co-workers for achieving grid-cost parity. [33] The immiscible catholyte and anolyte forming the biphasic system (acidic solution of hydroquinone (H 2 Q) and parabenzoquinone (pBQ) dissolved in PYR 14 TFSI) were subjected to cyclic voltammetry (CV) in 3-electrode electrochemical cells, separately. The shape of the CVs in Figure 2 denotes a quasi-reversible redox behavior for both electrolytes.…”

A biomimetic redox flow battery based on flavin mononucleotide

“…While less energy dense, RFBs using organic active materials have received increasing interest because of their promise to satisfy other important requirements such as low cost and sustainability. A variety of unique organic active materials have been reported for use in RFBs3678910111213, a number of which have been inspired by research in Li-ion and Na-ion batteries141516. The number of organic materials that can deliver stable cycling, however, has been very limited.…”

Towards Low Resistance Nonaqueous Redox Flow Batteries

“…6,[8][9][10][11] Furthermore, the use of nonaqueous solvents enables a broader palette of potentially inexpensive active materials, which could significantly lower RFB costs. 7,12 In contrast to their aqueous counterparts, nonaqueous redox flow batteries (NAqRFBs) are a nascent technology, which have yet to realize economically feasible performance.8 To date, most NAqRFB studies have focused on molecular discovery and electrolyte characterization at dilute active species concentrations, [13][14][15][16][17][18][19] with only a few published attempts to engineer higher performance systems with concentrated electrolytes. [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.…”