In situ surface engineering O3-layered oxide cathode via Na3PO4/P3-layered oxide dual coating layers

Transition metal layered oxides have emerged as promising cathodes for sodium-ion batteries (SIBs), yet suffer from sluggish kinetics and serious capacity attenuation due to surface side reactions, microcracks and surface residual alkalies. One effective improvement strategy typically by single surface coating is used to boost electrochemical performances. Here, a dual-surface-coated O3-NaNi 0.4 Fe 0.2 Mn 0.4 O 2 (NFM) cathode is prepared using the in-situ formed Na 3 PO 4 /P3-NFM during the thermal decomposition reaction of NH 4 H 2 PO 4 . The Na 3 PO 4 coating layer, formed by NH 4 H 2 PO 4 and the residual sodium species on the surface of O3-NFM, serves as a protective layer; while the P3-NFM, with layered structure anchored firmly on the O3-NFM surface, facilitates fast Na + diffusion kinetics. The Na 3 PO 4 /P3-NFM coatings rebuild the interface as a stable and fast path for Na + transport, enhance the interface stability, and restrain the adverse factors for interfacial side reactions, intragranular cracks and irreversible phase transformations. Consequently, the optimized cathode exhibits satisfactory rate capabilities (130.6 mAh g −1 at 1C and 90.0 mAh g −1 at 10C), and a favorable cyclability (75.6 % after 300 cycles at 1C), as well as an excellent air stability. These results promise a highly effective improvement strategy for boosting electrochemical performances of promising layered oxide cathodes for SIBs.