Lily Robertson1,2,Ilya Shkrob1,2,Shi Li1,2,Haimeng Wang1,2,Garvit Agarwal1,2,Yuyue Zhao1,2,3,Ryan Walser-Kuntz1,4,Melanie Sanford1,4,Rajeev Assary1,2,Lei Cheng1,2,Lu Zhang1,2
Joint Center of Energy Storage Research1,Argonne National Laboratory2,Indiana University-Purdue University3,University of Michigan4
Lily Robertson1,2,Ilya Shkrob1,2,Shi Li1,2,Haimeng Wang1,2,Garvit Agarwal1,2,Yuyue Zhao1,2,3,Ryan Walser-Kuntz1,4,Melanie Sanford1,4,Rajeev Assary1,2,Lei Cheng1,2,Lu Zhang1,2
Joint Center of Energy Storage Research1,Argonne National Laboratory2,Indiana University-Purdue University3,University of Michigan4
Redox flow batteries (RFBs) are proposed to fill the supply-demand gap in the renewable energy market. Nonaqueous RFBs are of special interest due to their wider electrochemical windows compared to aqueous systems and compatibility with redox-active organic molecules (redoxmers). However, engineering stability in these systems is highly dependent on redoxmer, electrolyte salt, and solvent. Here, we examine 2,1,3-benzothiadiazole (BzNSN), a negative charge carrier for nonaqueous RFBs. Our previous work revealed significant solvation effects in acetonitrile depending on the cation of the electrolyte, where lithium cations strongly coordinate the BzNSN radical anion and shift its half-wave potential 150-200 mV positive depending on counter-anion. This shift is accompanied by decreased redoxmer stability as shown by spin resonance and symmetric H-cell cycling experiments. We hypothesized that a solvent with strong lithium binding would alleviate the redoxmer-cation chelation effect. For this task, <i>N</i>,<i>N</i>-dimethylacetamide (DMA) was explored as preliminary calculations showed that it should interact strongly. Comparing lithium vs. tetraalkylammonium electrolytes showed no shift in half-wave potential in this solvent. Further, there was little change in radical anion stability by spin resonance experiments. Finally, we compared symmetric H-cell cycling of BzNSN in the two solvents in lithium-based electrolyte and found that DMA had successful cycling while the acetonitrile experiment barely cycled. This study reveals the importance of solvation effects in evaluating new materials for nonaqueous RFBs.<br/><br/>The research was financially supported by the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.