In Operando Probing of Sodium-Incorporation in NASICON Nanomaterial: Asymmetric Reaction and Electrochemical Phase Diagram

NASICON-type materials are one of the most promising cathodes for sodium-ion batteries (SIBs) due to their stable structure and the three-dimensional framework for the migration of Na⁺. During the usage of SIBs, they should hold the ability to endure sudden changes in temperature and current density, which have a profound impact on battery life. However, little research focused on the reaction mechanism under the above situations. Here, the phase transformation processes of NASICON-type material, Na₃V₂(PO₄)₃, are investigated by applying high-resolution in situ X-ray diffraction and Raman coupled with electrochemical tests under different temperatures (273 and 293 K) and scan rates (0.5, 2, and 5 mV s^–1). The results demonstrate that the phase evolution process is one-phase solid solution during the desodiation process rather than the traditionally two-phase reaction at a high scan rate or low temperature. An electrochemical phase diagram is also drawn based on thein situ results, which can be used to explain the asymmetric result. This work can help with understanding the phase evolution process of NASICON-type cathodes, as well as guiding the application of SIBs in various working conditions