关键词: 石墨烯, 氧化亚铜, 半导体, 异质结, 锂离子电池, 电子输运

Materials with hybrid metal-semiconductor nanostructures, such as graphene-metal oxides and carbon nanotube-metal oxides, have been intensively exploited as electrode material for lithium ion batteries in recent years. It was found that the structures and properties of the metal-semiconductor herterojunction and the energy level structures of the semiconductor are essential for the conductance of the metal-semiconductor composite. It is thence believed that the conductance, and thus the lithium-storage performance, of the metal-semiconductor composite can be improved by tuning the structures of the metal-semiconductor herterojunction and the energy level structures of the semiconductor. Metal excess defects can occured in metal oxide crystals due to the anion are absent from their its lattice sites or the presence of an extra cations at in an interstitial sites. In the metal excess type metal oxide, the electric transport is mainly by "excess" electrons which are present for maintaining the electrical neutrality, and thus possesses a higher conductance. In this work, graphene-wrapped Cu₂₊₁O/Cu composites were successfully fabricated by using a hydrothermal reaction followed by an in situ thermal reduction. The structures, surface morphologies and the lithium-storage performances of the obtained materials were characterized and investigated by scanning electron microscopy, X-ray diffraction and galvanostatic discharge-charge techniques. In the obtained hybrid material, highly-crystallized Cu₂₊₁O (Cu₂O with metal excess defects) successfully formed during the heat treatment processes, Cu₂₊₁O and Cu particles were homogeneously wrapped by flexible graphene sheets with a well defined core-shell structure. Constant current charge-discharge results showed that graphene-wrapped Cu₂₊₁O/Cu composite had a higher reversible capacity and excellent cycling stability, delivered a higher initial charge-discharge capacity of 773 and 438 mA•h•g^-1 at 50 mA•g^-1 and superb cycling performance of 368 mA•h•g^-1 after 60 cycles, as well as a favorable rate capabilities and high rate cycling performances, indicating the high conductance and the optimized herterojunctions were achieved by the simultaneously introduction of metal excess defects, metallic copper and graphene in graphene-wrapped Cu₂₊₁O/Cu composites.

Key words: graphene, cuprous oxide, semiconductor, heterojunction, lithium ion batteries, electron transport