CAREER: Controlling dimensionality and ligand connectivity to tune intercalation properties in transition metal oxychlorides

PART 1: NON-TECHNICAL SUMMARY Improving further rechargeable Li- and Na-ion battery technologies can only be achieved by enhancing simultaneously their energy density and their scalability. To date, nickel- and cobalt-based layered oxides and lithium iron phosphate are regarded as stellar materials, all suffering from geographical sourcing constraints. To reduce the need for critical materials, strategies relying on partial substitution of metals or stabilization of novel polymorphs have classically been deployed. With support from the Solid State and Materials Chemistry Program in NSF’s Materials Research A Section, the principal investigator and his research group evaluate mixed anion materials, namely layered oxychloride materials, as a new class of intercalation materials with tunable chemical and physical properties with the potential to develop a novel material pipeline for battery applications. Despite their technological relevance, these materials have thus far been considered too fragile to be intercalated and used as battery materials. Using suitable liquid electrolytes, layered oxychlorides can be stabilized and their intercalation properties unlocked. By spanning a range of compositions, structure/property relationships are established to inform the development of lithium and sodium battery materials. Besides the fundamental knowledge gathered in this project, the principal investigator organizes outreach activities to engage students in grade 8-12, including first generation students local to the Boston area, through involvement with the Pine Manor Institute for Student Success at Boston College. Additionally, educational opportunities for undergraduate and graduate students are offered through the development of a seminar series and class content, strengthening the pipeline of future researchers in the field of energy applications. PART 1: TECHNICAL SUMMARY This project, with support from the Solid State and Materials Chemistry Program in NSF’s Materials Research A Section, advances the fundamental understanding of mixed anion materials used as intercalation compounds for energy applications. The objective of the proposed research is to reveal the role of structural properties, including network dimensionality and connectivity, on controlling intercalation sites and cationic distribution in layered oxychloride materials. To tackle the innate instability of oxychloride when exposed to liquids, novel highly concentrated electrolytes will be used. By tuning the transition metal to ligand ratio as well as oxygen to chlorine ligands ratio, and comparing one-dimensional, two-dimensional and three-dimensional oxychloride materials, it is hypothesized that both the redox and diffusion properties can be modulated. With the help of crystallographic studies and the development of novel calorimetric techniques, phase diagrams for lithium and sodium orderings are established for these materials, and the activation energy for phase-front diffusion of ordered phases evaluated. By comparing various materials with similar stoichiometry and structure, the role of electrostatic interactions in intercalation behavior can be revealed. Collectively, this work advances the development of Li- and Na-ion battery materials, establishing novel family of intercalation materials made of abundant and geographically disperse precursors. The research efforts are complemented by educational components including a summer elective class for students in grade 8-12 local to the Boston area and classroom exposure to the rich chemistry of mixed anion materials for undergraduate and graduate students. 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.