Recent attention has been focused on the synthesis and application of complex heter ostructured nanomaterials, which can have superior electrochemical performance than singlestructured materials. Here we synthesize the threedimensional (3D) multicomponent oxide, mnmoo 4 /Comoo 4 . Hierarchical heterostructures are successfully prepared on the backbone material mnmoo 4 by a simple refluxing method under mild conditions; and surface modification is achieved. We fabricate asymmetric supercapacitors based on hierarchical mnmoo 4 /Comoo 4 heterostructured nanowires, which show a specific capacitance of 187.1 F g − 1 at a current density of 1 A g − 1 , and good reversibility with a cycling efficiency of 98% after 1,000 cycles. These results further demonstrate that constructing 3D hierarchical heterostructures can improve electrochemical properties. 'oriented attachment' and 'selfassembly' crystal growth mechanisms are proposed to explain the formation of the heterostructures.
Ultralong hierarchical vanadium oxide nanowires with diameter of 100-200 nm and length up to several millimeters were synthesized using the low-cost starting materials by electrospinning combined with annealing. The hierarchical nanowires were constructed from attached vanadium oxide nanorods of diameter around 50 nm and length of 100 nm. The initial and 50th discharge capacities of the ultralong hierarchical vanadium oxide nanowire cathodes are up to 390 and 201 mAh/g when the lithium ion battery cycled between 1.75 and 4.0 V. When the battery was cycled between 2.0 and 4.0 V, the initial and 50th discharge capacities of the nanowire cathodes are 275 and 187 mAh/g. Compared with self-aggregated short nanorods synthesized by hydrothermal method, the ultralong hierarchical vanadium oxide nanowires exhibit much higher capacity. This is due to the fact that self-aggregation of the unique nanorod-in-nanowire structures have been greatly reduced because of the attachment of nanorods in the ultralong nanowires, which can keep the effective contact areas of active materials, conductive additives, and electrolyte large and fully realize the advantage of nanomaterial-based cathodes. This demonstrates that ultralong hierarchical vanadium oxide nanowire is one of the most favorable nanostructures as cathodes for improving cycling performance of lithium ion batteries.
Recently, nanostructured materials have attracted great interest in the field of lithium-ion batteries, essentially because of their substantial advantages, such as short transport path lengths for both electrons and Li + ions, a large amount of contact surface area between the electrode and electrolyte, and large flexibility and toughness for accommodating strain introduced by Li + insertion/extraction. [1][2][3] Among the transition-metal oxides, nanostructured MoO 3 has been extensively investigated as a key material for fundamental research and technological applications in optical devices, smart windows, catalysts, sensors, lubricants, and electrochemical storage. [4][5][6][7] There are two basic polytypes of One might take advantage of the intrinsic structural anisotropy of a-MoO 3 for tuning its properties by interlayer structural modification, annealing, and lithiation. [5,8,9] In this Communication, we report the electroactivity of a-MoO 3 nanobelts after lithiation that show superior performance to nonlithiated a-MoO 3 nanobelts. An X-ray diffraction (XRD) measurement was performed using a D/MAX-III X-ray diffractometer. Fourier-transformed infrared (FTIR) absorption spectra were recorded using the 60-SXB IR spectrometer. Raman spectra were taken using a Renishaw RM-1000 laser Raman microscopy system. Scanning electron microscopy (SEM) images were collected with a JSM-5610 and FES-EM LEO 1530. Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED) were recorded by using a JEOL JEM-2010 FEF microscope. The electrochemical properties were studied with a multichannel battery testing system. Batteries were fabricated using a lithium pellet as the negative electrode; 1 M solution of LiPF 6 in ethylene carbon (EC)/dimethyl carbonate (DMC) as the electrolyte; and a pellet made of the nanobelts, acetylene black and PTFE in a 10:7:1 ratio as the positive electrode. The fabrication of a single nanobelt-based device has been described in detail elsewhere. [10] XRD measurement was first used to study the phase and lattice modification of the nanobelts before and after lithiation (Fig. 1A). The diffraction peaks of the XRD pattern for both samples can be readily indexed to be orthorhombic with lattice constants of a = 3.962 Å, b = 13.85 Å, c = 3.697 Å (International Centre for Diffraction Data (ICDD) No. . No peaks of any other phases were detected, indicating the high purity of the MoO 3 nanobelts. For the non-lithiated MoO 3 nanobelts, the stronger intensities of (020), (040), and (060) peaks than those for the bulk MoO 3 (Fig. S1, Supporting Information) indicates the anisotropic growth of the nanostructure as well as the preferred orientation of the nanobelts on the substrate. Importantly, in comparison to the nonlithiated sample, there is a small shift of the (020) peak toward a lower diffraction angle for the lithiated sample. This is direct evidence of an expanded b-plane interlayer distance for 0.065 Å after lithiation, ...
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