A novel method for preparing lithium manganese oxide nanorods from nanorod precursor
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- Liu, H. & Tan, L. J Nanopart Res (2010) 12: 301. doi:10.1007/s11051-009-9614-1
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Lithium manganese oxide nanorods were prepared from manganese dioxide nanorods precursor. The structure and morphology were confirmed by X-ray diffraction (XRD) and transmission electron microscope (TEM). The data of the Rietveld refinement indicate that the nanorods preferentially grow along the  direction. After charge–discharge test at 1.0 mA cm−2 in 3.0–4.4 V, the nanorods LiMn2O4 showed the 134.5 mAh g−1 initial discharge capacity and only lost 1.1% of initial capacity after 30 cycles, which is better than that of bulk particles LiMn2O4 prepared by traditional solid-state reaction method. This effective and simple route to synthesis nanorods LiMn2O4 from one-dimensional (1D) precursor could also be extended to prepare 1D other nanomaterials with special electrochemical properties.
Over the past several decades, the spinel LiMn2O4 has been extensively studied as the most promising positive electrode material to replace LiCoO2 for lithium-ion batteries because of several advantages such as low cost, less toxicity, easy preparation, safe to handle, etc. (Blyr et al. 1998; Liu et al. 2007; Lim 2008). Nevertheless, the reversible capacity and the cycling stability of this compound have to be improved for the Jahn–Teller distortion, manganese dissolution, and decomposition of the electrolyte (Thackeray 1997; Amatucci et al. 1997).
Recently, nanostructured LiMn2O4 cathode shows better electrochemical properties than conventional electrodes because the distance over which Li+ diffuse is decreased dramatically (Kang and Goodenough 2000; Kang et al. 2001). Furthermore, the larger surface area of the nanostructured electrode makes higher experiment capacity (Che et al. 1998; Li et al. 2000). Among various nanomaterials with different morphologies, one dimensional (1D) nanostructures (nanotubes, nanowires, and nanorods) LiMn2O4 show a great advantage over that of other morphologies (Li et al. 2000; Nishizawa et al. 1997). One-dimensional nanostructure offers the shortest distance and the largest surface for Li+ transport in the solid state. In addition, by controlling the dimensions of the nanostructres, the unwanted oxidation of water during the charge process can be eliminated and good cyclability can be obtained (Li and Dahn 1995).
Much effort, such as the template method (Nishizawa et al. 1997), hydrothermal solid-state synthetic method (Li et al. 2000), a self-seeded, surfactant-directed growth process (Zhang and Yu 2003), has then been devoted to developing new approaches to prepare 1D LiMn2O4 cathodes. However, to the best of our knowledge, the synthesis of a 1D nanostructure of LiMn2O4 with nanorods structure has not been reported to date.
We here for the first time report a novel method for preparing lithium manganese oxide nanorods from nanorod precursor, which may provide the possibility of detecting the theoretical capacity limits of LiMn2O4 with the smallest dimension structures, and also could be extended to prepare other 1D nanomaterials with special electrochemical properties.
The starting material of nanorods MnO2 used in this work can be prepared as described previously (Xun and Yadong 2002). LiOH · H2O with analytical grade and the as-prepared nanorods MnO2 in quantities corresponding to 0.1 mol stoichiometric LiMn2O4 were mixed thoroughly in a mortar and heated at 700 °C for 8 h, followed by air cooling to room temperature to obtain the final products. As a contrast to nanorods LiMn2O4 in this work, the bulk particles LiMn2O4 prepared by traditional solid-state reaction method were also characterized.
Phase identification and evaluation of lattice parameters of the product were carried out by powder X-ray diffraction (XRD, Bruker D8-advance, Germany). The XRD patterns were collected by steps of 0.02° in the range of 10° ≤ 2θ ≤ 70° with a constant counting time of 0.1 s per step at room temperature, and the Rietveld analysis used the TOPS R refinement software. The morphology was observed with a transmission electron microscope (TEM, FEI, TECNAI G220 S-Twin, America). The simulate cells were assembled by using lithium foil as anode and reference electrode in an argon–filled glove box, the as-prepared powders mixed with 12% acetylene black and 8% polytetrafluoroethylene (PTFE) as the cathode and 1 M LiPF6 in a 1: 1(V/V) mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) as the electrolyte, Celgard 2300 membrane as the cell separator. The charge–discharge cycle was performed at a constant current density of 1.0 mA/cm2 in a potential range of 3.0 and 4.4 V using the simulate cells. All the electrical measurements were carried out by a battery testing system (BTS-5 V/3A, Neware technology limited corporation, China) at room temperature.
Results and discussion
Lithium manganese oxide nanorods were prepared from manganese dioxide nanorods precursor. The phase has been characterized by XRD. The structure refinement data indicated that the nanorods preferentially grew along the  direction. The product morphology was further confirmed using TEM. After charge–discharge test at 1.0 mA cm−2 in 3.0–4.4 V, the nanorods LiMn2O4 showed the 134.5 mAh g−1 initial discharge capacity and only lost 1.1% of initial capacity after 30 cycles.
This work was supported by Hubei Provincial Natural Science Foundation of China (No. 2007ABA345).