| In recent years, the demand for lithium ion batteries (LIBs) in electric and hybrid vehicles is increasing. Exploring high capacity, long cycle life and high safety of lithium ion battery anode materials has attracted more and more attention. With the emergence of global environmental problems, developing low cost, rich and environmentally friendly materials is more and more important. At present, due to its high specific capacity, transition metal oxides have been widely studied. Among them, iron oxides with high specific capacity, abundant resources and low cost, green environmental protection and other advantages, is a new type of lithium ion battery anode material with a good prospect of application. However, due to the large volume change in the process of cell cycle, poor conductivity of itself, the iron oxides in the commercial use have been limited.Recently, the plant wastes as widespread and inexpensive materials, attracted the attention of many scholars in all ages. Its large specific surface area, the porous nature of the advantages is as lithium material needs, so the application of plants in the anode materials for lithium ion batteries rapidly rises.To improve the poor stability and the low initial coulombic efficiency of iron oxides, we make full use of the natural plant waste. The plant here is used as the template and (or) carbon source in the process of material synthesis. On the one hand, it can increase the conductivity of the material; on the other hand, it can buffer the volume expansion of iron oxides during charging and discharging, so as to achieve the purpose of improving the electrochemical performance of the material. Specific research contents and results are as follows:1. We used a natural plant flower spikes of Typha orientalis, as the bio-templates and organizers to prepare a novel two-dimensional (2D) porous print fabric-like α-Fe2O3 sheet. The material contains two kinds of pore structures, one is the pore with diameter of about 30 nm, and the other is the pore channel with aspect ratio of ca.4. The results show that pre-treatment by ammonium for flower spikes has a great effect on the microstructure and electrochemical performance of the products. As the anode material for lithium ion batteries (LIBs), the as-obtained porous print fabric-like α-Fe2O3 sheets show an initial discharge capacity of 2264 mA h g-1 and the specific capacity of 1028 mA h g-1 after 100 cycles at a current density of 500 mA g-1, which is higher than the theoretical capacity of α-Fe2O3 (1007 mA h g-1). This highly reversible capacity is attributed to the very thin large-area sheet structure, many pores or pore channels among the interconnected nanosheets, which could increase lithium-ion mobility, facilitate the transport of electrons and shorten the distance for Li+ diffusion, and also buffer large volume changes of the anodes during lithium insertion and extraction at the same time. The synthesis process is very simple and broadly applicable, providing a green and mass production approach toward high-performance energy storage materials.2. The natural plant flower spikes of Typha orientalis as the template and the carbon source were employed to synthesize γ-Fe2O3/C composite nanorods by hydrothermal method and the subsequent calcination. When used as anode materials for lithium ion batteries, the composite shows the initial discharge capacity of 1089 mA h g-1 at a current density of 500 mA g-1, and the specific capacity decreased to 470.5 mA h g-1 at the 170th cycle. After that, with the cycle of material increasing, the capacity slowly rises, the discharge capacity of the material reaches 621.8 mA h g-1 at the 267th cycle. The charge-discharge cycle results show good capacity and rate performance of the battery. The special performance of the composite material is due to its special porous nanorod structure, which can shorten the transmission path of the ions and electrons in axial and radial directions. Furthermore, the outer wrapping of the carbon source can effectively increase of electrical conductivity and the specific surface area, so that the composite presents good electrochemical performance.3. We put forward a new strategy for using the discarded disposable peanut shell as template and carbon source to prepare one-dimensional Fe3O4/ porous carbon (PSC) nanocomposite pillars. The used disposable peanut shells were converted into uniform porous carbon as well as combined with the Fe3O4 nanoparticles formed in situ simultaneously. The result shows that the diameter of the nanopillar is about 40 um, with aspect ratio of ca.15. The specific surface area of composite is 244.32m2/g and pore size distribution is mainly in the range of 5-40 nm. The content of carbon in the composite is 80%. When Fe3O4/PSC composite was used as anode material for lithium-ion battery, the initial discharge capacity of the battery reached 2255.613 mA h g-1 at the current density of 100 mA g-1, while it was still 718 mA h/g after 100 cycles. The charge-discharge cycle test result shows good capacity and rate performance of the battery. Our strategy presents a scalable route for transforming peanut shells waste into Fe3O4/PSC, offering a very promising way to make sustainable anodes for LIBs and economical multi-functional carbon-based hybrids available for other practical applications. |
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