Yolk-shell Prussian blue nanoparticles with fast ion diffusion for sodium-ion battery

•A template-free method was proposed for PBAs to obtain a yolk-shell structure.•The YSPB electrode delivers a high capacity of 140 mA h g−1.•The cycling stability is enhanced by the yolk-shell structure.•The yolk-shell structure helps accelerating the sodium ion diffusion. Prussian blue analogues as cathode material for sodium-ion batteries suffer from poor cycling stability and inferior rate performance because of crystal defects and sluggish ion diffusion kinetics. The Na1.02Fe[Fe(CN)6]0.95·□0.05 Prussian blue nanoparticles with few lattice vacancies and a yolk-shell structure are designed and synthesized to address these two problems. The hierarchical structure endows yolk-shelled Prussian blue nanoparticles with large specific surface area, large pore volume and short ion pathways. As a result, the yolk-shell Prussian blue nanoparticles exhibit a high discharge capacity (140 mA h g−1 at 0.1C), high-rate performance (51 mA h g−1 at 10C) and excellent cycling stability (95.8% capacity retention after 500 cycles at 1C).