Engineering principles for sustainable organic electrode materials

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Lithium-ion batteries have become one of the leading electrochemical energy storage systems driving the progress of modern electronic technologies. However, the production of conventional lithium-ion batteries relies on finite and unsustainably sourced transition metals, such as lithium and cobalt, which will inevitably restrict their application in the long term. In this research project, the investigators seek to develop new organic electrode materials as alternative energy storage media in batteries. These new battery materials are made of abundant elements, such as carbon, nitrogen, oxygen, and sulfur, and can provide a more economical and sustainable route to renewable energy storage. These research activities are integrated with the training of graduate and undergraduate students in addressing scientific challenges at the interface of electrochemistry, synthetic chemistry, and machine learning. The educational aims include developing a laboratory exercise for an undergraduate general chemistry course that will introduce students to connections between electrochemistry and environmental water quality testing and a mentoring program for these students which connects them with peer tutors. Organic electrode materials (OEM) are promising alternatives to unsustainably sourced transition metals as energy storage media in lithium-ion batteries. Current OEMs (primarily redox organic polymers), however, suffer from (a) poor conductivity (30% carbon loading required), (b) poor cycling stability (ca. 100 cycles), and (c) sloping/multiple-stage voltage profiles. The overall goal of the research project is to discover, elucidate, and apply engineering principles to improve the rechargeability of OEMs. First, a wide array of novel small-molecule OEMs featuring strong intermolecular interactions are prepared. In-situ and ex-situ spectroscopic studies are performed to understand how the intermolecular interactions between charge storage units change as a function of state-of-charge. These tasks will explore the hypotheses that complementary hydrogen bonding and pi-pi stacking improve the stability of quinone-fused aza-phenazine OEM materials. It is predicted that additional intermolecular disulfide bonds between sulfur-rich thiazyl charge storage units can improve conductivity and facilitate high-rate cycling of OEMs. These results and new fundamental understanding will be used to develop new design principles for optimizing the conductivity, stability, voltage profile of OEMs through modification of molecular structure. In the second part of the proposal, the research project seeks to develop machine learning-based models that can (a) predict the long-term cycling life of OEMs using data collected from short-term high-throughput tests and (b) recommend new highly stable OEMs based on physical organic descriptors. This systematic study will ultimately reveal unintuitive design principles that enable more focused research efforts in place of extensive trial-and-error screening.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.