²³Na Solid-State NMR Analyses for Na-Ion Batteries and Materials

Sodium-ion batteries (NIBs) have received considerable attention as next-generation batteries that complement or replace the current demand for lithium-ion batteries. For the development of NIBs, elucidating the states of sodium ions and understanding the charging-discharging mechanism on the electrodes is indispensable for achieving high capacity, high efficiency, long life, and reasonably safe performance. Solid-state nuclear magnetic resonance (SS-NMR) is a powerful tool for obtaining direct information on nuclei as it can detect information on sodium and distinguish different electronic circumstances. In this minireview, recent progress on NMR analyses of NIB electrode materials (cathode and anode) is outlined. ²³Na NMR signals of NaMnO₂-type cathodes, which are usually affected by the strong effect of paramagnetic species and other cathode materials, are introduced. Additionally, NMR analyses of hard carbon, graphite, and other inorganic anode materials are summarized.