Fabrication and Lithium-Storage Performances of Graphene-Wrapped Cu₂₊₁O/Cu Composites

Abstract

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 anions are absent from their lattice sites or the presence of extra cations at 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 Cu 2 ＋ 1 O/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 Cu 2 ＋ 1 O (Cu 2 O with metal excess defects) successfully formed during the heat treatment processes, Cu 2 ＋ 1 O 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 Cu 2 ＋ 1 O/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 Cu 2 ＋ 1 O/Cu composites.

Bottom-up synthesis of nitrogen-doped graphene sheets for ultrafast lithium storage

“…2,3 By virtue of its extraordinary physicochemical properties, including large surface area, high conductivity, structural exibility and chemical stability, graphene has been intensively explored as an electrode material and/or a substrate of hybrid materials for high performance lithium ion batteries (LIBs). [4][5][6][7][8][9][10][11][12][13][14] It is commonly estimated that graphene might be more suitable for reversible lithium storage than commercial bulk graphite, because the graphene sheets could double the sorption capacity by binding the lithium ion on both sides of the graphene plane and by shortening the lithium diffusion distance. 4,5,[15][16][17][18][19][20] However, it is recently concluded that the lithium coverage on the surface of single layer graphene is actually smaller, because of the lower binding energies of lithium to carbon and the strong Coulombic repulsion of the lithium atoms on the opposite sides of graphene as well as the small charge transfer between lithium and graphene.…”

Cu2+1O/graphene nanosheets supported on three dimensional copper foam for sensitive and efficient non-enzymatic detection of glucose

“…In Fig. 2 23 successfully formed during hydrothermal the process, and Cu foam as 3D conducting scaffold were homogeneously coated by exible graphene sheets. Fig.…”