Morphology-controlled graphene nanosheets as anode material for lithium-ion batteries

Abstract

Morphology-controlled graphene nanosheets can be easily synthesized as anode material for application in high-capacity lithium-ion batteries. A modified version of an improved method for higher degree of oxidation of graphite oxide (GO) has been developed and characterized. X-ray diffraction analysis shows that GO prepared using this method has a higher degree of oxidation than that of using the improved method. The interlayer d-spacing increases from 0.87 nm (using the improved method) to 0.92 nm (using the modified-improved method). Also, it is confirmed by XPS analysis that the O/C ratio in GO increases from 2.51 (improved method) to 8.27 (modified-improved method). It is hypothesized that GO, which has a higher degree of oxidation, is more reducible to graphene. The more reduced graphene has a larger amount of free pi-bonds and fewer layers, and it can be easily altered to morphology-controlled graphene. Graphene nanosheets prepared using the modified-improved method exhibits discharge capacities of 1079 mAh g(-1) (at a constant current of 40 mA g(-1)) and 1002 mAh g(-1) after 50 cycles. The capacity retention of the synthesized graphene nanosheets is 1070 mAh g(-1) at a current of 40 mA g(-1) after the rate capability test, and their rate capability is 463 mAh g(-1) at a current of 400 mA g(-1). The morphology-controlled graphene nanosheets prepared by the modified-improved method shows better discharge performance compared to graphene prepared by the improved method.