Synthesis and Electrochemical Properties of InVO4 Nanotube Arrays
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0922-U01-06
Synthesis and Electrochemical Properties of InVO4 Nanotube Arrays Ying Wang, and Guozhong Cao Materials Science and Engineering, University of Washington, Seattle, WA, 98195 ABSTRACT A capillary-enforced template-based method is described for the preparation of InVO4 nanotube arrays. Nanotube arrays of InVO4 were prepared by filling the InVO4 sol into pores of polycarbonate membranes and pyrolyzing through sintering. Another type of InVO4 nanotube arrays (InVO4/acac) are obtained from the sol with the addition of acetylene acetone (acac). For comparison purposes, InVO4 films were prepared by drop casting from InVO4 same sol. Films and the two types of nanotube arrays of InVO4 annealed at 500ºC consist of mixed monoclinic (InVO4-I) and orthorhombic (InVO4-III) phases. The nanotubes are perpendicular to substrate surface with the outer diameter of ~200 nm for short InVO4 nanotubes and ~170 nm for long InVO4 nanotubes. InVO4/acac nanotube array has the highest charge capacity (790 mAh/g), followed by InVO4 nanotube array (600 mAh/g) then InVO4 film (290 mAh/g). Such enhanced lithium-ion intercalation properties are ascribed to the large surface area and short diffusion distance offered by nanostructures and amorphisation caused by acetylene acetone. INTRODUCTION Orthovanadate compounds with a general formula M3+VO4 (M3+ = In, Fe, Cr, Al, and rare earths) have aroused much interest due to their lithium ion intercalation properties [1]. Among them, InVO4 is particularly interesting because of its high intercalation capacity and good cyclicity, and is thus a promising candidate for anode material in lithium secondary batteries [1]. The electrochemical properties of InVO4 powders have been thoroughly studied by Denis et al.1 To make thin films of InVO4, a sol-gel route based on vanadium oxoisopropoxide and indium nitrate has been utilized in combination with dip-coating [2]. Addition of acetylene acetone(acac) results in a more stable sol and the resultant InVO4 dip-coated film shows lower crystallinity in comparison with those films obtained from the same sol without acetylene acetone and sintered at the same temperature [3]. Electrochemical and electrochromic properties of the InVO4 films obtained from the sol-gel route have been investigated [3]. Compared to films of pure orthorhombic phase, or mixed monoclinic and orthorhombic phase, InVO4/acac films exhibit the highest capacity (between 30 and 40 mC/cm2), and their electrochemical stability is more than 1000 cycles. This alcoholic sol-gel route has the advantage of providing clear and homogenous sol which gives rise to highly transparent film, however, the resultant films consist of mixed phases if sintered at temperatures lower than 600ºC, although the monoclinic and orthorhombic phases of InVO4 have similar electrochemical and electrochromic properties. Nanomaterials are attracting great interest for electrochemical energy storage, due to their high surface area and short diffusion distance [4]. InVO4 nanoparticles have been synthesized and their photoc
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