Sn4P3@Porous carbon nanofiber as a self-supported anode for sodium-ion batteries

Sn4P3 is a promising anode material for sodium ion battery (SIBs). However, Sn4P3 suffers from a large volume expansion during cycling, which leads to electrode fragmentation and a bad cycling performance. To solve this issue, Sn4P3 nanodots was encapsulated into a porous, free-standing, carbon nanofiber (designated as Sn4P3@CNF) using electrospinning combined with a thermal treatment. Good capacity and long-term stability are achieved and are attributed to the unique fiber structure and the ultra-small Sn4P3 particle size (≈8 nm). The porous structure allows electrolyte to easily penetrate into the fiber, enhancing the number of electrochemical reactions sites. Furthermore, the voids in the porous fiber effectively accommodate the volume expansion during sodiation and desodiation. Based on this rational structure, a high reversible capacity above 710 mA h g−1 was achieved after 200 cycles. A full SIBs using the Sn4P3@CNF anode and a Na3V2(PO4)3 cathode showed a good average operating voltage of 3 V and a high energy density of 252 Wh kg−1. This work demonstrates the great potential of Sn4P3@CNF as a promising anode for the next generation of SIBs.