Preparation, Characterization, and Electrochemical Performance of Lithium Trivanadate Rods by a Surfactant-Assisted Polymer Precursor Method for Lithium Batteries A. Sakunthala, †,‡ M. V. Reddy,* ,† S. Selvasekarapandian,* ,‡,§ B. V. R. Chowdari,* ,† and P. Christopher Selvin | Department of Physics, National UniVersity of Singapore, Singapore 117542, DRDO-BU, Centre for Life Sciences, Bharathiar UniVersity, Coimbatore 641046, India, Kalasalingam UniVersity, Krishnankoil, Virudhunagar 626190, Tamil Nadu, India, and NGM College, Pollachi, Tamil Nadu, India ReceiVed: January 20, 2010; ReVised Manuscript ReceiVed: March 30, 2010 Lithium trivanadate (LiV 3 O 8 ) compound was prepared under different conditions and characterized by the Rietveld-refined X-ray diffraction, scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area and density techniques. The electrochemical performances of the LiV 3 O 8 compounds prepared under different conditions were compared. LiV 3 O 8 rods prepared by the surfactant-assisted polymer precursor method were found to perform well, delivering a discharge capacity of 230 ((5) mA · h/g at the end of the second cycle, with an excellent capacity retention of 99.52% at the end of the 20th cycle, for a current density of 30 mA/g. LiV 3 O 8 rods delivered a discharge capacity of 135 ((5) mA · h/g at the end of 350 cycles, for a current density of 240 mA/g, and reasonably high capacity values were achieved at the different current rates. Impedance spectroscopic studies during the first and eighth cycles at various voltages are analyzed and discussed. 1. Introduction Nanostructured materials play an important role in advanc- ing electrochemical energy storage and conversion technolo- gies such as lithium ion batteries and fuel cells, offering great promise to address rapidly growing environmental concerns and the increasing global demand for energy. 1 For example, literature studies show that V 2 O 5 nanostrips obtained by the polyol method have an improved initial discharge capacity owing to the nanostructured morphology of the compound. 2 Nanosized and rodlike LiMn 2 O 4 has been found to achieve good electrochemical performance. 3 LiFePO 4 microstructures with self-assembled nanoplates synthesized by a solvothermal method deliver better cell performance than the corresponding commercial material. 4 Li 1+x V 3 O 8 has been investigated as a cathode material for the past 20 years. Its crystal structure 5 consists of a layered monoclinic structure belonging to the space group P2 1 /m. The structure is made up of (V 3 O 8 ) (1+x)- layers in the b-c planes, stacked one above the other along the a axis, which, in turn, consists of two basic structural units, VO 6 octahedra and VO 5 distorted trigonal bipyramids interconnected to each other by corner-sharing oxygen atoms to form V-O layers. Between the V-O layers, there are different octahedral and tetrahedral sites for the lithium ions. Unlike in other layered structures, where the layers are held together only by weak van der Waals forces, in this compound, each layer is held together by Li + ions at the octahedral sites present in the interlayer. The immobile lithium ions play a pinning role between the layers and keep the layers strongly connected. The excess lithium corresponding to the amount x is accommodated at the tetrahedral sites between the layers and takes part in charge/discharge processes. 6-9 Despite its structural advantages, the electrochemical performance of the above compound was found to be mainly influenced by the synthesis method. 10 Synthesis conditions such as temperature and raw materials used and morphological characteristics of the final product such as size, shape, texture (agglomerations), and crystallinity were found to influence its electrochemical performance. 11,12 The compound LiV 3 O 8 has many advantages such as low cost, high energy density, and good safety characteristics. 10,11 The moderate working voltage (2.5-3.5 vs Li) 7 and high-temperature stability of this compound when compared to those of other cathode materials such as LiCoO 2 (4.0 V vs Li), 13 LiMn 2 O 4 (4.0 V vs Li), 1 and LiFePO 4 (3.4 V vs Li) 1 make it more suitable for use in lithium polymer batteries. Intensive research has been carried out on this cathode material as reported by many authors. 10,14,15 The preparation of LiV 3 O 8 by a sol-gel method, other oxides, and electrochemical properties were discussed in detail by Fu et al. 16 The LiV 3 O 8 compound has been prepared and studied by many different methods such as a sol-gel process, 12,17-19 electrospinning combined with a sol-gel process, 20,21 hydro- thermal process, 22-24 freeze-drying, 25 a citric acid and peroxide sol-gel method, 26 spray drying, 11 a rheological phase reaction method, 27 an ultrasonic method, 28 a flame pyrolysis method, 29 a low-heating solid-state method, 30 a microwave sol-gel route, 31 a microwave solid-state synthesis, 14 a low-temperature reaction route, 32 and an ethylenediaminetetraacetic acid (EDTA) sol-gel method. 33 In the present work, LiV 3 O 8 nanostructures were prepared by a simple preparation method within a short calcination time of 2 h. The structural and energy storage properties of the material were analyzed, and detailed electro- chemical impedance spectroscopy studies were performed. * Corresponding authors. E-mail: phymvvr@nus.edu.sg (M.V.R.), sekarapandian@yahoo.com (S.S.), phychowd@nus.edu.sg (B.V.R.C.). Tel.: 65-651662605 (M.V.R.). Fax: 65-67776126 (M.V.R.). † National University of Singapore. ‡ Bharathiar University. § Kalasalingam University. | NGM College. J. Phys. Chem. C 2010, 114, 8099–8107 8099 10.1021/jp1005692  2010 American Chemical Society Published on Web 04/14/2010