Solution Synthesis and Electrochemical Properties of V 2 O 5 Nanostructures
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Solution Synthesis and Electrochemical Properties of V2O5 Nanostructures Katsunori Takahashi1,2, Ying Wang1, Kyoungho Lee1,3 and Guozhong Cao1,* 1 Materials Science and Engineering, University of Washington 302 Roberts Hall Box 352120, Seattle WA 98195, USA * Email: [email protected] 2 Steel Research Laboratory, JFE Steel Corporation Kawasaki-cho, Chuo-ku, Chiba 260-0835, Japan 3 Division of Materials and Chemical Engineering, Soonchunhyang University 646 Eupnae-Ri, Shinchang-Myun, Asan-Si, Chungnam, Korea ABSTRACT We have prepared Ni-V2O5·nH2O core-shell nanocable arrays for Li+ intercalation applications. Ni-V2O5·nH2O nanocables were prepared via formation of Ni nanorod arrays through the template based electrochemical deposition, followed by coating of V2O5·nH2O on Ni nanorods through electrophoretic deposition. Transmission electron microscopy (TEM) micrograph clearly shows the Ni core was covered completely by a V2O5·nH2O shell. Electrochemical analysis demonstrates that in a current density of 1.6 A/g, the Li+ intercalation capacity of Ni-V2O5·nH2O nanocable array is approximately 10 times higher than that of singlecrystal V2O5 nanorod array and 20 times higher than that of sol-gel-derived V2O5 film. Both energy density and power density of such nanocable-array electrodes are higher than the V2O5 film electrode by at least one order of magnitude. Such significant improvement in electrochemical performance is due to the large surface area and short diffusion path offered by the nanostructured V2O5·nH2O. INTRODUCTION Electrochemical intercalation is to store electroactive species based on fast reversible faradic reactions occurring at or near the surface of an intercalation compounds. Electroactive species in electrolyte reduces at the surface and diffuses into the interior of the crystal structure of the intercalation compound, i.e., solid electrode, in response to an externally applied electric field [ 1 ]. Vanadium pentoxide (V2O5) is a typical intercalation compound with a layered structure [2], and thus one of the most promising materials for applications in electrochemical pseudocapacitors and electrochromic smart windows because of its Li+ intercalation ability [3]. In electrochemical pseudocapacitors, the amount of energy stored is proportional to the amount of the electroactive species that can be absorbed by the electrode. Electrochromic property arises from the change of valence state of vanadium through the intercalation process. For these applications, charge/discharge rate and intercalation capacity are the most important parameters. Since the diffusion coefficient of Li ion in V2O5 (10-12-10-13 cm2/s [ 4 , 5 ]) and electrical conductivity of V2O5 (10-2-10-3 S/cm [6,7]) are rather small, intercalation process is slow and only a surface layer is active in intercalation. Nanostructured materials possess large surface area (or a large surface to volume ratio) and a short diffusion distance, and thus offer promises to achieve significantly enhanced intercalation capacity, faster intercala
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