Hollow hierarchical microsphere structure endows the P2-type Na0.67Ni0.33Mn0.67O2 cathode material with excellent Na+ diffusion kinetics and cycling stability

P2-Na 0.67 Ni 0.33 Mn 0.67 O 2 is considered a promising cathode material for sodium-ion batteries. However, its practical application is still hindered by sluggish Na + diffusion kinetics and structural degradation caused by repeated Na + intercalation/deintercalation during cycling. Herein, by transforming the precursor structure from olive-like hierarchical structure to the peanut-like hierarchical structure, and finally to a microsphere-like hierarchical structure, a P2-Na 0.67 Ni 0.33 Mn 0.67 O 2 cathode material with a hollow hierarchical microsphere structure was obtained. This unique structure shortens Na  +  diffusion pathways, facilitates electrolyte infiltration, and effectively buffers volume variation during cycling. ICP-MS results indicate that the optimized sample has a relatively higher Na content, which may contribute to a higher charge capacity. SEM and XRD analyses after cycling reveal that the hollow hierarchical microsphere cathode suppresses particle fragmentation and structural degradation, while ex-situ XRD confirms its improved structural reversibility during charge/discharge. Intermittent current titration and multi-sweep cyclic voltammetry further demonstrate higher Na + diffusion coefficients. As a result, the optimized cathode delivers 79.3 mA h g −1 at 10C, corresponding to 76% of the capacity at 0.1C, and 75% higher than that of the olive-like cathode. It also achieves stable cycling for 2000 cycles at 5C, with capacity retentions of 87.51%, 76.83%, and 63.67% after 500, 1000, and 2000 cycles.