Synthesis of ZnO@Graphene composites as anode materials for lithium ion batteries

Zinc oxide (ZnO) nanocrystals attached to graphene nanosheets (GNs) have been fabricated by an efficient method, consisted of (i) microwave heating, (ii) modified Hummers' method, and (iii) homogenizing dispersion. Highly-crystalline ZnO nanocrystals, having a size of 80-100nm, are uniformly dispersed over the both sides of GNs and inserted into the interspacing layers, forming ZnO@GN framework. The ZnO@GN hybrids serve as anode material for the investigation of Li+ insertion/extraction at different rates. The as-prepared ZnO@GN anodes exhibit improved performance in terms of Li-storage capacity (850 mAh g(-1) at 0.1 C), high Coulombic efficiency (82.1% at 1st cycle), excellent rate capability (capacity retention similar to 60% at 5 C), and good cycling stability (capacity decay similar to 8% after 50 cycles), as compared with the fresh GN anode. The enhancement of performance can be attributed to the fact that well-dispersed ZnO nanocrystals serve as not only spacer to support the stereo GN framework but also redox site for enhancement of Li-storage capacity and ionic diffusion rate. (C) 2013 Elsevier Ltd. All rights reserved.