The present study enlightens a path towards empowering stable sodium batteries through incisive diagnostics of the multiscale fading mechanism in layered oxide materials (O3-NaNi1/3Fe1/3Mn1/3O2). With a suite of spatially resolved and ensemble-averaged spectroscopic and imaging studies, we reveal that the ubiquitous fading pathway of layered oxide primary particles involves a coupled anisotropic surface reconstruction and metal dissolution process that is initiated at the surface and gradually propagates into the subsurface. Upon extended cycling, we observe a significant buildup of intragranluar nanocracks that is attributable to the metal dissolution and phase change. Furthermore, we analyze the chemical evolution of each transition metal as a function of states of charge (SOCs) and cycling conditions. The surface Ni reduction occurs at all SOCs, whereas the surface Mn reduction primarily occurs at deeply discharged states. Additionally, the Fe and Mn dissolved from the cathode particles are detected by the X-ray photoelectron spectroscopy and the dissolution phenomenon is much more severe than expected. Finally, we develop surface passivation and elemental substitution approaches that can effectively alleviate the interfacial fading process and improve the battery performance. Therefore, our study sets a refined example for improving sodium cathode chemistry through the knowledge obtained from the advanced spectroscopic and imaging analysis.

Deciphering the cathode–electrolyte interfacial chemistry to stabilize sodium layered cathode materials

256th National Meeting (2018)

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