Three-dimensional hollow nitrogen-doped carbon shells enclosed monodisperse CoP nanoparticles for long cycle-life sodium storage

Transition metal phosphides are emerging as promising anode materials of sodium ion batteries (SIBs) due to their high performance in terms of capacity and operational stability. Highly isolated CoP nanoparticles encapsulated in 3D hollow nitrogen-doped carbon networks (CoP/HNC composite) are designed via polymerization of poly-dopamine (PDA) on ZIF-67 and the subsequent in-situ phosphorization. Ultrafine CoP nanoparticles (10 ± 2 nm) are decorated in nitrogen-doped carbon polyhedral shells in a porous 3D hollow architecture. Benefiting from the unique construction, the CoP/HNC electrode delivers a high reversible long cycle-life capacity of 223 mA h g⁻¹ for sodium storage at 500 mA g⁻¹ after 700 cycles. DFT simulations indicate that Na atoms strongly bound to CoP surfaces, and significantly concentrate near CoP surfaces, beneficial for the Na ions storage in this composite material. These results suggest the CoP/HNC composite can be a promising anode material for SIBs. Besides, the designed strategy of CoP/HNC composite could be applied to fabricate other metal phosphides for electrochemical storage devices.