Stepwise Hollow Prussian Blue Nanoframes/Carbon Nanotubes Composite Film as Ultrahigh Rate Sodium Ion Cathode

Prussian blue and its analogues (PBAs) have been proposed as promising cathode materials for sodium-ion batteries (SIBs) due to high theoretical capacity and low cost, but they often suffer from poor electronic conductivity and structural instability. Herein, a stepwise hollow cubic framework structure is first designed and a hybridized hierarchical film synthesized from single-crystal PBA nanoframes/carbon nanotubes (CNTs) composite is demonstrated as a binder-free ultrahigh rate sodium ion cathode. This hierarchical configuration offers improved tolerance for lattice expansion, reduced sodium ion diffusion path, enhanced electronic conductivity, and optimized redox reactions, thereby achieving the excellent rate capability, high specific capacity, and long cycle life. As expected, the developed FeHCFe nanoframes/CNTs electrode film exhibits a super high rate capacity of 149.2 mAh g(-1)at 0.1C and 35.0 mAh g(-1)at 100C. Moreover, it displays an excellent cycling stability with about 92% capacity retention at 5C after 500 cycles. This work will pave a new way to engineer advanced electrode materials for ultrahigh rate SIBs.