Elucidation of ligand-centered electrochemical reactivity in complex transition metal oxides

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NON-TECHNICAL SUMMARYBatteries store electrical energy through electrochemical reactions at electrodes. In the positive electrode of Li-ion technologies, these reactions involve a change in oxidation state of a transition metal in a solid compound. This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, pushes the limits of these reactions to increase the amount of energy that can be used between charges. The researchers investigate the ability of oxide ions in solids to change their electron count, in addition to the transition metal ions. They advance the understanding of this alternative reactivity by describing changes in exemplary compounds, in view of their stability and cyclability. The viability of this new chemical avenue to tailor materials which effectively store large amounts of electrical energy is established at a fundamental level. Such materials would boost the energy storage of Li-ion batteries, thereby transforming existing and emerging applications in portable electronics, transportation and the smart grid. This project also structures research experiences for undergraduate and high school students from Chicagoland, on topics relevant to modern challenges in chemistry and technology. Recruitment is vigorous among the highly diverse community at the University of Illinois at Chicago, to reach populations that are often recognized as underrepresented in STEM.TECHNICAL SUMMARYCurrent battery electrode materials are unable to reversibly accommodate redox changes of more than one electron per total transition metal content. The formal activity of transition metal centers is traditionally employed to account for chemical changes during these redox reactions. In oxides, recent studies suggest that bands with a large oxygen character can supply additional charge beyond the amount compensated at transition metal centers. The descriptions of the associated modifications of crystal and electronic structure, especially locally, remain deficient, and so is the understanding of the role of the specific transition metal. Furthermore, the reactions involve chemical states that could be unstable, potentially triggering secondary reaction pathways. This project, funded by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, produces a comprehensive picture of the fundamental chemical and structural changes to assess reversibility, stability, and, therefore, viability. The researchers combine a suite of spectroscopic, diffraction and scattering techniques to gather insights into these processes. Their focus is on gathering the greatest chemical detail for model systems showing evidence of this novel reactivity, without constraints from technological applicability. The ability to control anion-only redox activity without irreversible reactions has the potential to unlock families of compounds that transcend existing frontiers in charge storage capacity. The educational component of this project aims at encouraging undergraduates at the University of Illinois at Chicago to pursue research activities in energy applications, an economic sector that continues to witness job growth and demands highly skilled professionals, by providing mentorship in structured experiences with the team. Through outreach activities, the researchers also convey the importance and value of chemistry and energy to K-12 students in 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.