Abstract
Na-ion batteries, with their lower cost and earth abundance, are being actively researched for large-scale applications due to their similar intercalation chemistry to Li-ion batteries. The development of positive electrode materials is an important theme for achieving high-performance Na-ion batteries. Among these, Na layered materials have been studied for several decades, showing diverse crystal structures and high capacities. This presentation reports on the enhanced electrochemical performance achieved by substituting Li in the representative O3 and P2 structures of Fe-Mn based Na layered materials. Analysis of the crystal structure of materials, combining synchrotron X-ray diffraction and neutron diffraction techniques, revealed that Li can be located at the alkali site or transition metal site in the layered structure, depending on the composition of transition metals and the amount of Na. The redox behaviors of transition metals by Li substitution was also investigated using synchrotron X-ray absorption spectroscopy. The structural stability of Li-substituted layered materials during desodiation/sodiation was confirmed through in situ synchrotron X-ray diffraction analysis. Lastly, the improvements in electrochemical performance and structural stability were attributed to changes in Na ion diffusion behavior and honeycomb ordering, as elucidated by density functional theory calculations. These results indicate that Li substitution combined with appropriate structural design is a highly effective strategy for obtaining electrochemically stable electrode materials with layered structures for Na-ion batteries.
Published Version
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