Preparation And Modification Of MnO/C Microsheets And Their Electrochemical Performance

MnO has many advantages, such as high theoretical capacity (756mAh g-1), low cost, environmental benignity, high density (5.43g/cm-3), and low electrochemical motivation force (1.032V vs. Li+/Li), but its poor conductivity and large volume change during discharge/charge makes it poor cycling stability and rate capability as an anode material for Lithium-ion batteries. So far pepole have conducted many modification researches. Many studies indicate that nanosized materials with high specific surface area could offer more active sites for lithium ions, and special nanostructures could accommodate the volume change. Thus, deliberately designing special nanostructures is an effective strategy to improve the electrochemical performance of MnO anode materials.In this study, microsheet-like MnO/C composites are synthesized by sintering polyurethane (PU) sponge grafted with manganese polyacrylate. A distinct structural characteristic of the microsheets is that MnO nanoparticles are embedded homogeneously in carbon sheets with lateral sizes of a few microns, forming hierarchical architectures from micron to nanometer length scales. By investigating the influence of experimental conditions on the structure and electrochemical performance of MnO/C microsheets, it is revealed that the carbon content and morphology of the MnO/C microsheets are strongly dependent on the concentration of Mn(Ac)2solutions, and carbon content has a significant impact on the lithium storage properties of the MnO/C microsheets. Comparing the pyrolysis temperature of800℃with1000℃, the MnO/C microsheets obtained under the former condition have higher capacity. Compared with manganese nitrate, using acetic acid manganese can possess better Lithium storage capacity. In contrast, such as pyrolysis time, ion exchange time, have little effect on the electrochemical properties of the pyrolysis products.MnO/C microsheets synthesized from0.15M of Mn(Ac)2solution have a thickness of about1μm and carbon content of17.1wt%. The MnO/C microsheets exhibit excellent lithium storage performance. At current density of100and2000mA/g, the microsheets delivered a reversible capacity of711.2mAh/g, and after50cycles, a delithiation capacity of797.6mAh/g was still retained. At current densities of0.2,0.4,0.8,1.6, and2.0A/g, the electrode delivers delithiation capacities of598.5(20th),522.8(30th),429.4(40th),342.7(50th), and323.2mAh/g (60th), corresponding to84.1%,73.5%,60.3%,48.2%, and45.4%of the value at0.1mA/g (i.e.711.2mAh/g), respectively. Moreover, the electrode recovers its capacity to760.3mAh/g (70th) when the current density is decreased stepwise to100mA/g, implying that the structural stability of MnO/C microsheets could be keeped at high rate. Finally, Mn-Zn-O composite oxides with various Mn/Zn molar ratios are obtained by sintering polyurethane (PU) sponge grafted with the complex of manganese polyacrylate and zinc polyacrylate at800℃. The Mn-Zn-O/C oxides with a molar ratio of2:1obtain an initial charge capaicty of605.0mAh/g, and a high reversible capacity of612.4mAh/g after50cycles at100mA/g, which exhibits a good cycle stability.