Enhanced rate performance of cobalt oxide/nitrogen doped graphene composite for lithium ion batteries

Abstract

Ultrafine Co₃O₄ nanocrystals homogeneously attached to nitrogen doped reduced graphene oxide (rGO) by the hydrothermal reaction method are demonstrated as anode materials for lithium ion batteries. Transmission electron microscope images revealed that the crystal size of Co₃O₄ in Co₃O₄/N-rGO and Co₃O₄/rGO is 5–10 nm, much smaller than that of bare Co₃O₄, indicating that the reduced graphene oxide sheets with Co₃O₄ nanocrystals attached could hinder the growth and aggregation of Co₃O₄ crystals during synthesis. The graphene sheets can also effectively buffer the volume change of Co₃O₄ upon lithium insertion/extraction, thus improving the cycling performance of the composite electrodes. The doped nitrogen on the reduced graphene oxide can not only improve the conductivity of the graphene sheets, but also introduce defects to store lithium and enhance the connection of the Co₃O₄ nanocrystals to the graphene sheet, leading to better distribution of Co₃O₄ on the graphene sheets, and enhanced rate performance. The nitrogen doping combined with the unique structural features is a promising strategy for the development of electrode materials for lithium ion batteries with high electrochemical performance.