Regensburg 2025 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 16: Energy Storage and Batteries I
CPP 16.3: Talk
Tuesday, March 18, 2025, 10:15–10:30, H34
XPS study of redox mechanism in Na2.5-xFe1.75(SO4)3 cathode material for high-voltage sodium-ion batteries — Neama Imam1, •Karsten Henkel1, Anna Milewska2, Janina Molenda2, and Jan Ingo Flege1 — 1Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Germany — 2AGH University of Krakow, Faculty of Energy and Fuels, Krakow, Poland
A multiplet splitting model based on the original work by Gupta and Sen has been used to track the redox mechanism and electronic structure of Na2.5-xFe1.75(SO4)3, a high-performance cathode material for sodium-ion batteries (SIBs). This high-purity, off-stoichiometric open-channel cathode material with a tailored sodium-ion distribution, synthesized using an optimized solid-state route, demonstrates a high operating voltage of ~3.8 V, surpassing the values reported for other cathode materials in the literature. X-ray photoelectron spectroscopy (XPS) was employed to analyze the evolution of the material's electronic structure at various charging potentials. Fe2p3/2 spectra decomposition using the multiplet splitting model revealed the gradual oxidation of Fe2+ to Fe3+ during sodium de-intercalation while transitioning from its pristine state with the presence of Fe2+ at the cathode surface only to the fully charged state (Na0.89Fe1.75(SO4)3 at 4.5 V). This result is consistent with the electrochemical analysis.
Keywords: sodium-ion batteries; Na2.5-xFe1.75(SO4)3; polyionic cathode material; XPS; multiplet splitting model