Microwave irradiation synthesis of Co3O4 quantum dots/graphene composite as anode materials for Li-ion battery

• Co3O4 quantum dots/graphene composites are fabricated via microwave irradiation method.
• Uniform Co3O4 nanocrystals of 3-8 nm are homogeneously dispersed on graphene nanosheets.
• Reversible capacity of the composite retains 1785 mAh g−1 after 90 cycles at 0.1 C.
• Co3O4 quantum dots/graphene can tolerate high current cycling and have good retention of capacity.
• Enhanced performances could result from quantum and size effects of quantum dots.

Co3O4 quantum dots/graphene composites were synthesized by a facile and efficient microwave irradiation method, and they were analyzed using XRD, TEM, HRTEM, and TG. Uniform Co3O4 nanocrystals of about 3-8 nm with a high density are homogeneously dispersed on graphene nanosheets. When used as anode materials for Li-ion batteries, the Co3O4 quantum dots/graphene composites show a significantly enhanced cycling performance (1785 mAh g−1 at 0.1 C after 90 cycles) as well as high rate capability (485 mAh g−1 at 5 C). The reversible capacity is found to be much higher than the theoretical value. The superior performance could be attributed to the interfacial lithium-storage and the quantum and size effects of quantum dots that lead to high activity during the lithiation/delithiation process. In addition, the flexible and conductive graphene nanosheets and well dispersed Co3O4 nanodots as well as the synergetic effect between them also benefit the electrochemical performance by endowing a superior high surface area and shortening the diffusion pathway of lithium ions.

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