Structural complexity in prussian blue analogue k-ion cathode materials John Cattermull 1,2 , Andrew Goodwin 2 , Mauro Pasta 1 1 Materials, University of Oxford, UK, 2 Inorganic Chemistry, University of Oxford, UK Prussian blue analogues (PBAs) are a framework material that are of great interest for use as cathode materials in Na- and K-ion batteries. Whilst Na-ion PBA batteries have been commercialized for use in stationary storage and are now in development for use in electric vehicles, the high operating potential of K-ion PBAs offers the exciting prospect of use in electric vehicles where high specific energy density is necessary. Attempts to maximise the specific capacity of PBA cathodes have been made by eliminating [Fe(CN) 6 ] vacancies [1] . Whilst making these low-vacancy materials has been made possible by altering the synthesis, optimising the electrochemical performance has proved more challenging. Accessing the full capacity with high retention on cycling is one problem, and achieving the same excellent rate capability of the high-vacancy PBAs is also non-trivial. High-vacancy PBAs have an apparent simple cubic structure, but the low vacancy PBAs with high K-ion content have structural distortions [2] . The subsequent phase transitions on cycling these low-vacancy materials are believed to be responsible for poor capacity retention and rate capability. We report the structure of PBA cathode materials along with their thermal and electrochemical response [3] . Their structure-property relationships are illustrated, which lead to ideas for materials design for the optimization of their performance as cathode materials in a K-ion battery. References 1. Bie, X.; Kubota, K.; Hosaka, T.; Chihara, K.; Komaba, S. J. Mater. Chem. A 2017, 5, 4325. 2. Cattermull, J.; Pasta, M.; Goodwin, A. L. Mater. Horizons 2021, 8, 3178. 3. Cattermull, J.; Sada, K.; Hurlbutt, K.; Cassidy, S. J.; Pasta, M.; Goodwin, A. L. Chem. Mater. 2022, 34, 5000.
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