Chemical Bonding in Redox-Active Oxyfluorides

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NON-TECHNICAL SUMMARYRedox intercalation reactions are reactions during which electrons (negative charges) are transferred from one chemical building to a different one. In solid materials these reactions are essential to create battery technologies currently on the cusp of transforming human mobility. Ideally new electrode materials allow large changes of charge, which maximizes energy storage, but these changes must also be reversible for extensive cycling and long battery lifetimes. This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, seeks to build comprehensive descriptions of the chemical bond in oxyfluoride materials that are emerging as alternatives to pure oxides in cathodes for Li-ion batteries with high energy density. The researchers investigate the role of fluoride ions to manipulate the underlying redox reaction, with especial attention to its participation in charge compensation. The research not only assesses the viability and design rules of oxyfluoride materials as practical battery electrodes, but also amplifies existing general theories of bonding in inorganic crystalline solids. The research has the potential to inform the discovery and design of mixed-anion materials with groundbreaking properties, even beyond battery applications. The research topic provides the driver for an educational plan with the unified goal to guide students toward energy applications, an area of the job market where growth and demand are still just onsetting. Professor Cabana’s portfolio of education and outreach activities spans from elementary to graduate school, from local institutions to national events, with an emphasis in diversity by targeting members of Hispanic communities.TECHNICAL SUMMARYThe capacity of transition metal oxides as battery cathodes is maximized when high oxidation states can be achieved, but these states are not stable, leading to irreversibility and failure. Oxyfluorides have recently been explored as alternatives, but the resulting synergies between anions remain to be ascertained, particularly the role of the halide when metals reach high formal oxidation states. This project, funded by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, leverages and expands methodologies of X-ray spectroscopy to uncover the balance of burden of metals and anions in redox compensation of oxyfluorides. The research spans to phases with late metals because their high formal oxidation states are known to place the most stringent chemical demand on the anions, while also providing relevance to modern trends in batteries. This research aims to define fresh avenues to tailor materials to effectively and reversibly store large amounts of electrochemical energy, building new knowledge of the chemical bond that has the potential to transcend current boundaries of both chemistry and battery research. A tightly integrated educational component promotes materials chemistry and energy topics among the next generations. It includes outreach to local elementary schools and a national Summer workshop on the frontiers of research in electrochemistry. The researchers also recruit undergraduates to conduct projects in support of this research, including through partnerships with Hispanic organizations at the University of Illinois at Chicago.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.