SUSCHEM: Exploring Specific Heating in Microwave-assisted Synthesis of Hierarchical Hybrid Nanomaterials for Future Sustainable Batteries

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PART 1:   NON-TECHNICAL SUMMARYBatteries are ubiquitous electrical energy storage devices in our life to support anything from portable electronics to electrical grids. A key component that determines the cost and performance of batteries is the electrode materials. This project, funded by the Solid State Materials and Chemistry Program in the Division of Materials Research at NSF, seeks to develop new methods to prepare novel electrode materials that can be used for two types of emerging batteries, i.e. sodium ion batteries and magnesium ion batteries. These new battery-types use earth-abundant sodium and magnesium ions in electrochemical reactions and hence have the potential to significantly lower the cost of energy storage compared to current state-of-the-art Li-ion batteries, making them attractive for large-scale electrical energy storage. However, currently used single-phase electrode materials in these batteries exhibit poor stability and a short lifetime due to hosting the much larger sodium ions and higher-charged magnesium ions. Therefore this project targets hybrid materials which consist of active electrode materials deposited on stable three-dimensional nanostructured carbon scaffolds. The research approach makes use of the relatively strong microwave absorption by the nanocarbon materials to accelerate the synthesis process and create strong hybrid materials that otherwise may be unstable in separated phases. In addition to creating a better understanding of the fundamental properties of hybrid solid state materials and potentially improving the performance of electrical energy storage devices, this project provides cross-disciplinary training to students from diverse backgrounds including underrepresented groups. All three aspects are critical for maintaining our nation's leading role in the strategically important fields of energy conversion and storage.PART 2:   TECHNICAL SUMMARYThis project, funded by the Solid State Materials and Chemistry Program in the Division of Materials Research at NSF, targets the development of well-controlled three-dimensional (3D) hierarchical hybrid electrode materials for two types of emerging batteries, i.e. sodium ion batteries and magnesium ion batteries, by depositing desired active electrode materials (metal oxides and chalcogenides) on nanostructured carbon templates using an innovative microwave-assisted synthesis method. Rapid heating, based on the specific microwave absorption of the nanocarbon templates, induces rapid nucleation and growth of metastable phases which combine into stable hybrid electrode materials that cannot be readily synthesized with conventional methods. Different types of nanocarbons, including dispersed nanoflakes of reduced graphene oxides (rGOs), stacked 3D films of carbon nanotubes (CNTs) or electrospun carbon nanofibers (CNFs), and arrays of vertically aligned carbon nanofibers (VACNFs), are investigated as highly conductive and mechanically robust templates to control the morphology, composition and phases of the deposited active electrode materials. This provides techniques for synthesizing delicate 3D hierarchical core-shell hybrid materials containing metastable materials such as hydrated metal oxides (V2O5·nH2O bilayers) and metal chalcogenides (VS4 chains) which have more opened structures to facilitate reversible storage of large Na+ ions and divalent Mg2+ ions. Such hybrid hierarchical materials may break the intrinsic limits of single-phase electrode materials by enhancing the electrical conductivity and reducing the ion diffusion path length in the solid materials while significantly improving the electrode's stability. The capability of fast heating by microwave irradiation shortens the materials synthesis processes and greatly accelerates materials discovery and optimization. This project also provides cross-disciplinary training to both graduate and undergraduate students in nanomaterials synthesis/characterization, electrochemistry and electrical energy storage technologies. Outreach activities are aimed at interesting K-12 students (particularly girls) in Kansas in STEM education, and engaging an undergraduate student from Xavier University (underrepresented minority) in summer research and further career development each year.