Ion Transport in Prussian Blue Cathode Materials for Na-Ion Batteries

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Large-scale harvesting of renewable forms of energy requires innovative energy storage solutions. Electrochemical energy storage in the form of Na-ion batteries (NIBs) offers a promising low-cost, clean, and safe choice for grid-scale storage. A central challenge that NIB materials currently face is that due to the larger ionic radius of the Na-ion compared to the Li-ion, ionic transport is often slowed down, decreasing charging rates and power densities. To improve the charging rates of established battery materials and search for new materials exhibiting fast ion transport, a sound understanding of the atomic-scale processes underlying ionic transport is indispensable. Such knowledge, deeply rooted in the defect chemistry of the materials, however, to date is lacking for many NIB materials. Information on the defect chemistry will also shed light on an experimentally observed phenomenon of decreasing electrochemical performance of several cathode materials with increasing water content. In this project, ionic transport will be explored in Prussian Blue, a model material for NIB cathodes with open-framework structures. These materials are good candidates for cathode materials with fast ion transport. Ionic transport will be investigated both at the atomic and at the macroscopic level with a powerful multi-disciplinary approach encompassing computational techniques as well as electrochemical investigations and solid-state nuclear magnetic resonance (NMR) spectroscopic studies. The transport mechanism of the inserted Na-ions will be analysed and the impact of water on the Na-ion transport will be elucidated. This will contribute to rendering ion transport in Prussian Blue-based materials more robust against the influence of water and searching systematically for new cathode materials with fast ion transport in the future.