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

• Graphene nanosheets was manufactured using a simple modified version of a previously improved Hummers method.
• The wrinkle-free graphene was easily manufactured from prepared graphene by post-process treatment.
• Morphology-controlled graphene nanosheets showed excellent discharge performance.
• Morphology-controlled graphene has the potential to be easily applied to graphene-wrapped composite.

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 π-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.

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