Unveiling The Correlation between Synthetic Parameter and Structural Stability of O-Redox Cathodes via Time-Resolved XRD Analysis on The Solid-State Synthesis

The demand for high-energy-density sodium-based batteries has led to the investigation of the oxygen-redox (O-redox) reaction to increase the theoretical capacities of conventional cathodes. This O-redox reaction is triggered by introducing substitutes or vacancies in the transition metal (TM) layer, which generate the non-bonding electrons of lattice oxygens, thus providing additional capacity [1]. In terms of O-redox stability, the atomic arrangement of substitutes or vacancies in TM layer, which affects the distance between redox-active oxygens and TM migration barrier, is considered crucial for determining O-redox stability [1-2]. However, the construction mechanism of O-redox cathodes during synthesis and its correlation with O-redox stability has not been fully understood.<br/>Herein, we aim to investigate the construction mechanism of O-redox cathodes during solid-state synthesis and evaluate their O-redox stability. Specifically, we monitor the evolving structure of cathode precursors using time-resolved X-ray diffraction (TR-XRD) analysis by controlling the synthetic parameter. Subsequently, in-depth structural studies on the cathodes are conducted using advanced characterization tools such as high-resolution electron microscopy (HR-TEM) and X-ray absorption spectroscopy (XAS). Our structural analyses reveal how the synthetic parameter influence the final cathode structure, and we further correlate these findings with the O-redox stability using the electrochemical tests.