| As the energy shortage and environmental pollution problems increasingly serious, developing renewable clean energy has gradually been established. It will play a vital role in reducing energy consumption and protecting ecological environment. In the field of renewable energy, rechargeable lithium-ion batteries(LIBs) have been widely used in portable electronic devices, electric vehicles, electric grids, by virtue of its high energy density, high working voltage, long cycle life, no memory effect. However, as a crucial part of LIBs, the commercial graphite anode has an inherent shortage of capacity(372 mA h g-1), which is inadequate to meet the growing requirements of high energy batteries. Therefore, to develop the alternative anode materials with high energy density is imperative. In 2000, transition metal oxide anode based on conversion mechanism was put forward and shows attractive merits as a potential candidate due to its high theoretical capacity(500-1000 mA h g-1), abundance, low cost, nontoxic, and ecofriendliness.In this paper, in order to explore green, low cost, synthesis simple anode material with excellent clectrochemical performance for LIBs, the transition metal oxide anode with high energy density was researched. And its structure design and preparation process was optimized through the methods of nanoarchitecture construction and combination with carbon materials. Moreover, the synthesis strategy, surface morphology, microstructure, and chemical composition of the as-prepared composite were examined in detail through XRD, SEM, TEM, XPS, Raman spectroscopy, N2 adsorption/desorption methods. As anode material, their lithium storage properties and reaction mechanism were thoroughly investigated.The contents are as following:(1) A nanostructured composite with Fe3O4 nanocrystals(~10 nm) highly dispersed on ordered mesoporous carbon(here, CMK-3) is successfully synthesized by a facile wet impregnation method. CMK-3 matrix takes a role in confining the particles growth and preventing particles agglomeration, because of its characteristic of homogeneous porous channels, high conductivity, large surface area. The composite Fe3O4@CMK-3 exhibits a large reversible capacity and good cycle stability with a retention value of 910 mA h g-1 at a current density of 200 mA g-1 over 50 cycles, as well as a capacity of 670 mA h g-1 even up to 100 cycles at 1000 mA g-1.(2) A novel foamlike Fe3O4/C composite is prepared via a sol-gel type method through a unique self-expanding process with gelatin as the carbon source and ferric nitrate as the iron source. With the interaction between ferrous nitrate and gelatin, the foam structure was achieved. The Fe3O4/C composite possesses abundant porous structure along with highly dispersed Fe3O4 nanocrystal embedment in the carbon matrix. In the constructed architecture, the 3D porous network property ensures electrolyte accessibility; meanwhile, nanosized Fe3O4 promotes the structure stability. As a result, this composite electrode demonstrates an excellent cycling stability with a reversible capacity of 1008 mA h g-1 over 400 cycles at 200 mA g-1, as well as a superior rate performance with reversible capacity of 660 and 580 mA h g-1 at 3C and 5C, respectively.(3) A porous hollow Fe3O4/C microsphere composite is prepared through one-pot spray drying method followed by a post-calcination treatment. It is found the carbon source plays an important role in the structure of composite. When the sucrose and polyvinylpyrrolidone is chosen as carbon source, a solid and hollow Fe3O4/C microsphere composite is achieved, respectively. Among them, the hollow one presents superior lithium storage performance. On this basis, large amounts of inorganic water-soluble NaCl salt are introduced as a template to realize the construction of porous structure on carbon shell. In the architecture, the interconnected porous channel structure ensures electrolyte accessibility; meanwhile, nanosized Fe3O4 highly dispersed on carbon shell shortens lithium ion diffusion path, releases the volume strain and promotes the structure stability. As anode materials for LIBs, all three kinds of composite electrodes demonstrate an excellent cycling stability with large reversible capacity. The solid and hollow Fe3O4/C microsphere composite electrodes demonstrate a reversible capacity of 613 and 813 mA h g-1 even up to 600 cycles at 200 mA g-1, respectively. The porous hollow Fe3O4/C microsphere composite delivers a capacity of 980 mA h g-1 at a current density of 200 mA g-1 over 300 cycles, as well as a capacity of 520 mA h g-1 even up to 1000 cycles at 1000 mA g-1.(4) A delicate structure of graphitic carbon-encapsulated α-Fe2O3 nanocomposite is in situ constructed via “Absorption – Catalytic graphitization – Oxidation” strategy, taking use of biomass matter of degreasing cotton as carbon precursor and iron(Ⅲ) acetylacetonate acts as iron source. With the assistance of the catalytic graphitization effect of iron core, onion-like graphitic carbon(GC) shell is made directly from the biomass at low temperature(650 ○C). The constructed architecture helps enhance the electrical conductivity and stability of the composite. As a result, the as prepared α-Fe2O3@GC composite displays an outstanding cycle performance with a reversible capacity of 1070 mA h g-1 after 430 cycles at 0.2C, as well as a good rate capability of ~ 950 mA h g-1 after 100 cycles at 1C and ~ 850 mA h g-1 even up to 200 cycles at a 2C rate.(5) The porous and highly-ordered 1D nanowire and 2D nanosheet NiCo2O4 arrays on nickel foam substrate are controllably prepared with different precipitation additives via mild solvothermal method, following a low temperature post annealing treatment. Furthermore, the morphology evolution of these two different kinds of precursors based on reaction time is also effectively investigation, and a possible growth mechanism is proposed to understand the formation of wire/sheet arrays. When directly studied as anode for LIBs, the NiCo2O4 nanowire arrays electrode exhibits a reversible capacity of 967 mA h g-1, and the nanosheet one delivers a larger reversible capacity of 1450 mA h g-1 after 400 cycles at 200 mA g-1. And the NiCo2O4 nanosheet arrays electrode also displays an excellent rate performance, it exhibits a capacity above 500 mA h g-1 even at a current density of 5000 mA g-1 over 500 cycles. Furthermore, the clectrochemical performance of NiCo2O4 nanosheet arrays electrode and conventional slurry-cast electrode are compared. The nanosheet arrays one shows obvious advantage on both the reversible capacity and cycle stability. |
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