Porous Carbon Spheres Doped with Fe3C as an Anode for High-Rate Lithium-ion Batteries

Abstract

The search of advanced anodes has been an important way to satisfy the ever-growing demands on high rate performance lithium-ion batteries (LIBs). It was observed that the capacity of Fe3C as an anode is larger than its theoretical one, which might be attributed to the pseudocapacity on the interface between the carbide and electrolyte. In this work, a novel carbon sphere doped with Fe3C nanoparticles was fabricated and tested as the anode in LIBs. In the first place, iron precursors were embedded in the cross-link polymer resorcinol-formaldehyde (RF) spheres via a facile hydrothermal reaction, in which RF served as the carbon source and ethanol as a dispersant agent. Consequently, the hydrothermal products were carbonized successively at 700°C under inert atmosphere to obtain porous carbon spheres doped with Fe3C. When the composite severed as an anode in LIBs, its discharge capacity increased to the largest during the first 250-400 cycles, then dropped down to a similar level of that after 1000 cycles at different current rates. The discharge capacity of the composite increased from ∼300mAhg−1 to ∼540mAhg−1 at the current of 100mAg−1 during the initial hundreds cycles, and even a discharge capacity of ∼230mAhg−1 at the current of 2000mAg−1. Moreover, it was observed that a discharge plateau gradually appeared between 0.7∼1.1V during the first hundreds of cycles. The electrochemical behaviors of the anode before 1000 discharge/charge cycles were compared with that after 1000 discharge/charge cycles by cyclic voltammetry and electrochemical impedance spectroscopy to find out the differences between their features. The high rate performance of LIBs might result from the decomposition of electrolyte and the pseudocapacity behavior presented on the interfacial (surface) lithium storage of the active materials.