| Summary: | 博士 === 國立成功大學 === 材料科學及工程學系 === 107 === We investigate the lithium storage properties of two kinds of materials as anode for LIB: graphene oxide (GO) and self-assembled hollow-sphere zinc oxide/reduced graphene oxide (ZnO/rGO) nanocomposite. GO is obtained by Hummers method controlled by the various process parameters. The ZnO/rGO hollow sphere nanocomposite is synthesized by a low temperature (95 °C) chemical solution reaction. For ZnO/rGO composite, the capacity is increased remarkably as compared to GO sheets, and this is due to the synergistic effects of both the components in the composite. The GO acts as a conductive buffer layer that promotes the conductivity, and suppresses the volume expansion of ZnO during the charge/discharge process. ZnO/rGO hollow sphere structure nanocomposite has higher capacity 605.36 mAh g-1, which is 4.5 times higher than GO (133.82 mAh g-1), after 20 cycles. The capacity variation with the charge-discharge rate of ZnO/rGO nanocomposite showed a higher capacity (299.95 mAhg-1 at 1700 mAg-1) than GO (20.09 mAhg-1 at 1488 mAg-1) after 32 cycles.
In the second part of the study, we synthesized the high performance of the MnO2/rGO nad Mn3O4/rGO nanocomposite as an anode electrode of a lithium-ion battery. The composite is synthesized by a low temperature (83 °C) chemical solution reaction, and shows relatively high specific capacities (660 mAh g-1) after 50 cycles. For MnOx/rGO composites, the cycling stability is increased remarkably as compared to that seen with individual MnOx, and this is due to the synergistic effects of both the components in the composite. The rGO acts as a conductive buffer layer that suppresses the volume change of MnOx, and simultaneously promotes the conductivity of MnOx. The functional groups of graphene oxide facilitate the formation of MnOx at low temperature and connecting with MnOx, thus improving the capacity and cyclic stability.
In this study, zinc oxide/manganese oxide and reduced graphene oxide were combined to prepare composites with nanostructures and applied to lithium ion battery anodes. When the transition metal oxide is combined with the reduced graphene oxide, the reduced graphene oxide acts as a buffer layer and a conductive layer, supressing the volume change of the manganese oxide during the lithiation/delithiation process and improving the conductivity of the material. And the transition metal oxide can increase the overall capacity and supress the phenomenon of re-stacking situation of reduced graphene oxide. MnO2/rGO nanocomposite and Mn3O4/rGO nanocomposite can not only maintain the capacity of 387.15 mAh g-1 and 631.49 mAh g-1 after 250 cycles charge/discharge test, respectively, but also maintaining 443.05 mAh g-1 and 549.35 mAh g-1, respectively when charge/discharge with high charge current density 2464 mAg-1 due to the synergistic effect.
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