Polydopamine-derived porous nanofibers as host of ZnFe 2 O 4 nanoneedles: towards high-performance anodes for lithium-ion batteries

In this work, highly mesoporous carbon nanofibers in free-standing mat form are successfully fabricated by single-spinneret electrospinning of polystyrene (PS) followed by coating the porous PS nanofibers via in situ polymerization of dopamine and subsequent annealing. The pores inside the nanofibers are mainly in the range of 10–50 nm and interconnected to each other, forming nanochannels. ZnFe 2 O 4 crystals can then be grown from the nanofibers via a solution route. Strikingly, ZnFe 2 O 4 nanoneedles are formed, which have diameter and length of about 8 nm and 70 nm, respectively, and are located evenly not only on the surface of the nanofibers but also inside the nanochannels. The ZnFe 2 O 4 /carbon composite nanofibers exhibit excellent cyclability and rate performance as anodes of lithium ion batteries (LIBs), in which the ZnFe 2 O 4 nanoneedles are the major active component with normalized capacity of 1000–1700 mA h g −1 at 0.1 A g −1 and 560 mA h g −1 at 5 A g −1 , respectively. The excellent properties can be ascribed to the very small diameter of the nanoneedles that ensures complete conversion reactions and alloying/de-alloying between Zn and lithium, the good contact of the nanoneedles with polydopamine-derived N-doped graphitic carbon that offer efficient electrical conduction, and the nanochannels that allow facile transport of the electrolyte and lithium ions.