Mechanistic Insights into Sodium Niobate Surface Coating for Enhanced Cycling Performance of MnCuFe‐Based Layered Oxides for Sodium‐Ion Batteries

Spray‐dried battery active materials exhibit high specific surface area and tap density, enhancing battery performance with superior rate capability and initial capacity. However, this morphological optimization induces severe interfacial side reactions, causing rapid capacity fading. Herein, this study reports a novel wet chemistry coating method using hydrogen peroxide as an activation agent. Inspired by niobium‐based oxide coatings for lithium‐ion battery materials, this method is adapted for the sodium system with P2‐type Na 7/9 Mn 6/9 Cu 2/9 Fe 1/9 O 2 layered sodium oxides. Despite the adverse effect of hydrogen peroxide on active material performance, this coating method retains significant advantages in time efficiency and scalability with uniform coating on the active material surface. Consequently, the surface modified material achieves remarkable capacity retention of 97% after 200 cycles at a current rate of 120 mA g −1 within a voltage window of 1.5–4.2 V with presodiated hard carbon electrode, much higher than that of pristine material (54%). Postmortem analysis of cycled electrodes and electrochemical impedance spectroscopy results confirm the well‐covered material surface with suppressed side reactions, extending the battery cycling life. Additionally, powder X‐ray diffraction and X‐ray photoelectron spectroscopy analyses validate the temperature‐dependent coating and substitution behaviors of the coating material.