Redox flow batteries (RFB) using water-soluble organic redox couples are a new strategy for low-cost, eco-friendly, and durable stationary electrical energy storage. To be useful, these molecules must have extreme (either high or low) oxidation/reduction potentials and high aqueous solubility. Like many molecular design problems, the search space of possible functional derivatives is too large to be completely explored with ab initio calculation, but cheminformatics methods can make the search tractable. In this talk, I'll describe our exploration of 105 possible thiophenoquinone derivatives. By using existing cheminformatics tools from the drug-discovery community to eliminate insufficiently soluble compounds from our pipeline,we reduced the space to a more tractable 103 compounds. Using exhaustive B3LYP/6-311+G(d,p) thermochemical calculations with SMD solvation model—which reproduce experimental reduction potentials to within ±0.04—we computed redox voltages and free energies of solvation for all of these compounds, resulting in 51 new candidates with the high solubility and wide voltage range needed for high performance aqueous RFB applications. This ab initio data-set provided us with the opportunity to develop and test cheminformatics and lead-screening strategies for finding high-performing battery materials. A group-additivity model predicts the redox potential to within ±0.09 V, and can be trained with as few as 200 examples. Surprisingly, the "quantum-free" group-additivity model was more accurate than models that used the ab initio LUMO energy or information from semiempirical Hückel calculations as descriptors. Using these models to perform simulated screening experiments, we found that "active" (high voltage or low voltage species) candidates could be identified with an enrichment factor of 2-6, depending on the model and framework type. Having validated this drug-discovery inspired approach with an exhaustive dataset (where we know the "right" answer), we are now applying this to the much larger space of phenazine derivatives for aqueous redox batteries, and will describe preliminary results on that effort.

Using drug discovery methods to accelerate the search for better battery materials

251st National Meeting (2016)

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