Porous FeO _x /carbon nanocomposites with different iron oxidation degree for building high-performance lithium ion...

Transition metal oxides have attracted lots of interest for lithium ion battery (LIB) due to the high theoretical capacity, however, the large specific volume change, low electrical conductivity and slow intrinsic lithiation/delithiation still limit the practical applications. In order to overcome the challenge, a novel type of high temperature annealing treatment for the synthesis of 3D porous FeO _x nanocrystals embedded in a partially carbon matrix as an example for high-performance LIB is reported. The FeO _x /carbon nanocomposites with coral-like architecture achieved at 700 °C (F700) exhibit good long term cyclability with a reversible capacity 1012 mAh g^-1 remain after 500 cycles at 1.0 A g^-1 and the high rate capacity with a reversible capacity of 233 mAh g^-1 even at extremely high current density of 20 A g^-1. These excellent electrochemical performances could be attributed to the 3D porous structure and carbon coating, which could not only provide excellent electronic conductivity and enough elastic buffer space to accommodate volume changes upon lithium insertion/extraction, but also effectively avoid agglomeration of the Fe₃O₄ nanocrystals and maintain the structural integrity of the electrode during the charge/discharge process.