CAS-Climate:Collaborative Research:Understanding How Electrochemical Cation Trapping in Metal Oxides Enhances Subsequent Reversible Insertion of Anions in Forming Metal Oxyhalides

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Non-technical Abstract: Greater adoption of renewable energy sources necessitates economical and scalable electric-energy storage solutions. Novel battery chemistry holds the key to much-needed next-generation electric energy storage technologies to enable a sustainable society. Conventional batteries utilize cation-focused battery chemistry, which means positively charged ions migrate during the charge and discharge of a battery. With this project, supported by the Ceramics program in the Division of Materials Research, researchers at Oregon State University and Vanderbilt University investigate a possible mechanism for anion-based batteries (with migrating negatively charged ions instead of positively charged ones) for grid storage. Anion batteries have a great potential to replace current cation batteries for scalable energy storage, but fundamental mechanistic understanding is lacking. The project generates knowledge about what chemical environment in the metal-oxide battery material is more suitable for the transport and storage of anions during battery operation. Only sustainable, earth-abundant elements are investigated in the project for the electrodes, including manganese- and iron-based oxides, halide ions, and hydroxide; they are coupled with inexpensive and safe aqueous electrolytes. The new battery chemistry, if developed successfully, will greatly benefit our society by providing a low-cost, environmentally friendly energy-storage solution in the future. As part of the project the PIs introduce state-of-the-art materials research of novel battery chemistry to students from underserved communities and disseminate the knowledge to the public through institutional tools such as an online course.Technical Abstract:The knowledge of electrochemical anion insertion in hosts remains limited, particularly when the hosts are metal oxides. Anion insertion in metal oxides is inherently challenging because the interstitials are lined with oxides that repulse incoming anions. This project, supported by the Ceramics program in the Division of Materials Research, precisely tackles this problem by transforming the local structures of metal oxides with trapped cations. Researchers at Oregon State University and Vanderbilt University elucidate a new ion insertion mechanism whereby the irreversible insertion of cations in metal oxides promotes the reversible anion storage to form metal oxyhalides. Their research tests the central hypothesis that cation trapping transforms the structure of metal oxides and the chemical environment such that the subsequent anion insertion is greatly enhanced. They elucidate how the cation trapping alters the local structures of metal oxides and how the anions interact with the trapped cations and advance our understanding of the chemical environment and the changes caused by cation trapping and the anion insertion. Utilizing the synergy of expertise in electrochemical and structural characterization and first principles predictive modeling, the researchers establish mechanistic understandings of this new mechanism by investigating the model structure of spinel Mn3O4, in which the trapped Zn-ions enhances chloride storage. The project also develops a general principle of the new mechanism across different cations to be trapped, metal oxides as hosts, and anion charge carriers. Additionally, the integrated experimental and computation studies lay the foundation for a promising new research field using anion insertion to form metal oxyhalides.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.