| High energy consumption on our daily life is depending on the exploration of green renewable resources and effective energy storage equipments which are the key for the replacement of fossil fuels and traditional energy sources. As energy storage devices, rechargeable Li-ion batteries (LIBs) recently become focus of intense research due to their advantages including lower weight, high gravimetric and volumetric energy density, high power density, long cycle life and low self-discharge property. Much research studies have been carried out in order to achieve high performance rechargeable LIBs. Among all the contents for LIBs, anode materials are a key factor to influence the cycling stability and specific capacity of the battery. In order to improve the energy density, rate of charge and discharge, and cycling stability of LIBs, a variety of efforts have been undertaken to explore new functional materials.Recently, there has been much interest relating to the study of mixed transition metal oxides (MTMOs) because of their high electrochemical activities owing to the complex chemical compositions and their synergetic effects, which make them owing high capacities typically 2～3 times higher than those of the graphite/carbon-based electrode materials. MTMOs are becoming more appealing than ever for the high-performance electrochemical energy storage/conversion devices such as lithium ion batteries (LIBs), electrochemical capacitors (ECs), metal-O2 batteries (MOBs), and fuel cells (FCs). Among different MTMOs, Mn-base oxides are the preliminary choice for use as an anode material, due to their obvious advantages including high specific capacities and low toxicity, cost, and operating voltage compared to the iron, cobalt and nickel-based oxides. The major drawback of Mn oxides as the anode material in LIBs is the large volume changes, low conductivity, and low coulombic efficiency observed in the first cycle. Thus, it is really serious challenge for chemical and material researchers to design rational route for synthesis of MTMOs anode materials with good structural stability and excellent electrochemical performances.In this paper, a general route has been developed to fabricate hierarchical porous Mn-based oxides (AxMn3-xO4,0≤x<3; A=Co, Zn, Ni, Cu, Fe) with twin-microsphere structure via a multiple strategy consisting of modified polyol avenue and subsequent thermal process. Monodisperse quasi-mesocrystal carbonate twin microspheres were firstly synthesized via an Oriented Attachment accompanied by Ostwald ripening. Then twin microsphere-structured oxides were fabricated by annealing the above precursors at 500％ for 4 h in laboratory air. When evaluated as anode materials for LIBs, Mn3O4, ZnMn2O4, and CoMn2O4 twin-microspheres exhibit high specific capacity with excellent rate capability and enhanced cycling stability, making them potential substitute for LIBs electrode materials.1. When used as LIBs anode material, Mn3O4 twin microspheres manifest good cycling stability and a higher specific capacity compared to other nano-structure manganese oxides. Its specific capacity can maintain 470 mAh/g after 90 cycles under a current density of 500 mA/g and still keep a steady trend. While tested at various current densities, the specific capacity of 572 mAh/g also can be remained during nearly 100 cycles.2. ZnMn2O4 twin microspheres as electrode show good cycling performance under a current density of 0.5 A/g in the voltage range of 0.01-3 V vs. Li+/Li. The initial charge and discharge capacities of the ZnMn2O4 twin microspheres electrode are 732 and 1106 mAh/g, respectively, corresponding to a coulombic efficiency (CE) of 66%. Starting from the second cycle, CE increases to more than 99%, and meanwhile the reversible capacity of ZnMn2O4 twin microspheres gradually increases to 815 mAh/g after 70 cycles and retains a high reversible capacity of 860 mAh/g after 130 cycles.ZnMn2O4 twin microspheres electrode also own good rate capacity. As the current densities increase from 0.2 to 0.5,1, and 2 A/g, the electrode shows capacity retention varying from 772 to 695,618, and 484 mAh/g, respectively. When the rate is further increased to 5 A/g, ZnMn2O4 twin microspheres still deliver a favorable capacity of 329 mAh/g. Remarkably, when the rate turns back to 0.2 A/g, the capacity can be retained as high as 1084 mAh/g over more than 190 cycles without any loss, and the Coulombic efficiency is almost 100%.3. CoMn2O4 twin microsphere electrode also displays a stable cycling performance with high coulombic efficiency, wherein it still retains a reversible capacity of 890 mAh/g and nearly 100% capacity retention after more than 70 cycles. Even at a high current density of 1000 mA/g, a reversible discharge capacity of 573 mAh/g is retained after continuous cycling for more than 50 cycles.The rate capability is further evaluated at different current densities ranging from 200 to 2000 mA/g. The specific capacities are 790,740,664,580, and 500 mAh/g at the current densities of 500,800,1000,1500, and 2000 mA/g, respectively. Noticeably, when the current rate turns back to 200 mA/g, the capacity can recover as high as 908 mAh/g even after 120 cycles without any loss. |
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