Enhanced electrochemical properties of ZnO encapsulated in carbon nanofibers as anode material for lithium-ion batteries

Abstract

The amorphous ZnO particles encapsulated in porous nitrogen-doped carbon nanofibers (ZnO@PN-CNFs) are synthesized by electrospinning process and heat treatment. The enhanced electrochemical properties of ZnO@PN-CNFs are based on the porous nanostructure, high length/diameter (L/D) ratio, doped nitrogen, and uniform distributed amorphous ZnO nanoparticles. The results show amorphous ZnO particles in carbon nanofibers avoid the pulverization and alleviated the volume expansion, as well as make the cycling of the anode quickly reach stable. Furthermore, the nitrogen-doped carbon improves electron conductivity while one-dimensional (1D) nanofibers with high L/D ratio own a short diffusion path and high electronic transportation efficiency along the longitudinal direction. Meanwhile, the porous nanostructure from urea pyrolysis produces thinner wall and further shortens the ionic transport distance. Therefore, high capacity and long-cycling life are achieved. And the ZnO@PN-CNF electrode shows a high discharge capacity (1073.2 mAh g−1 at 0.1 A−1) after 100 cycles. Moreover, the ZnO@PN-CNF electrode presents a high discharge capacity of 703.1 mAh g−1 even at 1 A−1 after 400 cycles. In this work, urea not only stops the ZnO from crystallization, leading to uniform distributed amorphous small ZnO particles, but also makes numerous pores in the carbon nanofibers, enlarging the touching area with electrolyte and shortening the transport distance to ZnO particles. It is a promising way by adding urea to alleviate volume expansion and pulverization of the crystal particles and then enhance the performance of electrode.