Electrospun hetero-CoP/FeP embedded in porous carbon nanofibers: enhanced Na kinetics and specific capacity.

The practical application of transition metal phosphides has been hampered by the inferior rate capability and large volume change during charging and discharging processes. To address this, the construction of metal phosphide heterostructures combined with a porous carbon skeleton is a promising strategy for providing fast charge transfer kinetics. Herein, hetero-CoP/FeP nanoparticles embedded in porous carbon nanofibers (CoP/FeP@PCNFs) are obtained by coaxial electrospinning and low-temperature phosphorization processes. By employing CoP/FeP@PCNFs as the anode for sodium-ion batteries, a large reversible specific capacity (459 mA h g-1 at 0.05 A g-1), excellent rate performance (46.4% capacity retention rate at 10 A g-1 relative to 0.05 A g-1) and long-term cycling stability (208 mA h g-1 at 5 A g-1 over 1000 cycles and 73.5% capacity retention) can be obtained. By virtue of the porous structure and heterogeneous structure, the electrochemical performance of the CoP/FeP@PCNF sample was greatly improved. The porous structure can promote the ion transport and accommodate the volume expansion. Density functional theory calculation confirms that the constructed heterostructure can generate a built-in electric field and facilitate the reaction kinetics of Na+. This work provides the basic guidance for the future development of energy storage materials by designing heterostructures with a porous structure.