Design And Preparation Of Nano-structured Manganese Oxide Electrodes For Lithium Storage Application

Lithium ion battery (LIB) is the most promising energy storage device in the fields of electric vehicles (EVs) and hybrid electric vehicles (HEVs) for its high voltage, high energy density and long life. In order to develop high-performance LIBs for EVs and HEVs, it is essentially to develop electrodes with high rate capability. Novel nanostructures of metal oxides have attracted much attention as improved anode materials because of their high capacities and possible high rate capability, which were attributed to their large specific surface area and the short electronic and ionic transport length in nanoscale.Currently, most commercial lithium-ion battery anode materials are graphite material, which possess lower charge-discharge potential and lower cost. However, there is a critical defect for graphite material, which is the low theoretical capacity (372 mAh/g). Meanwhile, due to the low density of the graphite material, the same quality of graphite occupies more space than other materials, which leads to a low energy density. These defects of graphite material greatly limit its application in EVs energy field and so on. In 2000, Tarascon et al reported a transition metal oxide with charge and discharge performance for lithium-ion batteries. Since then, the study of this novel class of lithium-ion battery anode materials attracted more and more attention.Among all the transition metal oxide, manganese oxide material (MnO and MnO2) stand out from the crowd. This is not only because of the high capacity (MnO:755 mAh/g, MnO2:1230 mAh/g, theoretical), non-toxicity and environmental friendliness, but also because of the lower charge-discharge potential, which is known to be the lowest charge and discharge potential in transition metal oxide materials. This paper mainly focuses on preparing manganese oxide electrode with superior lithium storage properties by specific and novel morphology and electrode structure.The main contents and results are listed below:1. A simple approach to fabricate MnO electrodes with a distinctive morphology of interconnected porous nanoflakes for high power LIB applications. It can deliver a high reversible capacity up to 648.3 mAh/g after 100 cycles at a current density of 246 mA/g, and a capacity up to 708.4 mAh/g in the 200th cycle after cycling with various current densities from 246 to 2460 mA/g. Even at the current density as high as 2460 mA/g, the electrode can deliver a capacity higher than 376 mAh/g.2. A facile approach was fabricated the porous MnO microspheres for application as a high-performance anode material of LIBs. It can deliver a high reversible capacity up to 1234.2 mAh/g after 300 cycles at 0.2 C, and a capacity of 690.0 mAh/g in the 500th cycle at 2 C. The high reversible capacity can be attributed to the formation of PGF and the gradual activation of the active material. The excellent electrochemical properties of the porous MnO microspheres come from their unique structure and morphology with a short transport path for Li-ions and a large active material/electrolyte contact area.3. A facile approach to fabricate the electrode consisted of the interconnected MnO2 nanoflakes on the 3D nanostructured SS palte for high-power LIB applications. The representative electrode delivers a reversible capacity up to 1387.1 mAh/g after 100 cycles at a rate of 0.2 C, and a capacity higher than 492.9 mAh/g at a rate as high as 5 C. Such a superior electrochemical performance indicates that the 3D nanostructured SS plate is a promising current collector for enhancing the areal capicity of the eletrodes.4. We have fabricated NiO/MnO2 nanoflakes array as a high-performance anode material which exhibited excellent lithium storage performance. The structure of the interconnected porous NiO/MnO2 nanosheets can accommodate the volume change during discharge/charge processes The NiO/MnO2 nanoflakes array electrode delivered a high reversible capacity up to 1000 mAh/g after 160 cycles at a rate of 1.0 C. It exhibited an excellent rate performance of a capacity about 787 mAh/g at 5.0 C.