Predicting the Solubility of Organic Energy Storage Materials Based on Functional Group Identity and Substitution Pattern.

Organic electrode materials (OEMs) provide sustainable alternatives to conventional electrode materials based on transition metals. However, the application of OEMs in lithium-ion and redox flow batteries requires either low or high solubility. Currently, the identification of new OEM candidates relies on chemical intuition and trial-and-error experimental testing, which is costly and time intensive. Herein, we develop a simple empirical model that predicts the solubility of anthraquinones based on functional group identity and substitution pattern. Within this statistical scaffold, a training set of 18 anthraquinone derivatives allows us to predict the solubility of 808 quinones. Internal and external validations show that our model can predict the solubility of anthraquinones in battery electrolytes within log S ± 0.7, which is a much higher accuracy than existing solubility models. As a demonstration of the utility of our approach, we identified several new anthraquinones with low solubilities and successfully demonstrated their utility experimentally in Li-organic cells.

Redox-active zinc thiolates for low-cost aqueous rechargeable Zn-ion batteries.

Aqueous zinc-ion batteries (AZIBs) are promising candidates for large-scale electrical energy storage due to the inexpensive, safe, and non-toxic nature of zinc. One key area that requires further development is electrode materials that store Zn2+ ions with high reversibility and fast kinetics. To determine the viability of low-cost organosulfur compounds as OEMs for AZIBs, we investigate how structural modification affects electrochemical performance in Zn-thiolate complexes 1 and 2. Remarkably, modification of one thiolate in 1 to sulfide in 2 reduces the voltage hysteresis from 1.04 V to 0.15 V. While 1 exhibits negligible specific capacity due to the formation of insulating DMcT polymers, 2 delivers a capacity of 107 mA h g-1 with a primary discharge plateau at 1.1 V vs. Zn2+/Zn. Spectroscopic studies of 2 suggest a Zn2+ and H+ co-insertion mechanism with Zn2+ as the predominant charge carrier. Capacity fading in Zn-2 cells likely results from the formation of (i) soluble H+ insertion products and (ii) non-redox-active side products. Increasing electrolyte concentration and using a Nafion membrane significantly enhances the stability of 2 by suppressing H+ insertion. Our findings provide insight into the molecular design strategies to reduce the polarization potential and improve the cycling stability of the thiolate/disulfide redox couple in aqueous battery systems.