Preparation of copper-doped LiV 3 O 8 composite by a simple addition of the doping metal as cathode materials for lithium-ion batteries Lifang Jiao a , Haixia Li b, ⁎, Huatang Yuan a, ⁎, Yongmei Wang a a Institute of New Energy Material Chemistry, Nankai University, Tianjin 300071, PR China b Department of Materials Science and Engineering, Xiamen University, Xiamen, Fujian 361005, PR China ABSTRACT ARTICLE INFO Article history: Received 31 March 2008 Accepted 9 May 2008 Available online 23 May 2008 Keywords: Lithium trivanadate Copper lithium trivanadate Composite materials Crystal structure Electrochemical performance The copper-doped LiV 3 O 8 was first prepared by mixing copper powder with solid-state synthesized LiV 3 O 8 in distilled water. The electrochemical performance of the copper-doped LiV 3 O 8 was compared with that of the undoped one. It was found that the electrochemical performance of the copper-doped sample is significantly improved, with an initial capacity of 265.0 mAh/g and a stabilized capacity of 227.7 mAh/g after 100 cycles. It indicates that the copper-doped LiV 3 O 8 could be easily prepared by a simple addition of the doping metal. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Lithium trivanadate, LiV 3 O 8 , has been investigated as both a cathode and an anode material for rechargeable lithium batteries during the past decade because of its high specific capacity, facile preparation, and stability in air [1–11]. The electrochemical perfor- mance, such as discharge capacity, rate capability, and cycle ability, are strongly influenced by the preparation method. For improving the electrochemical performance of LiV 3 O 8 , many methods have been proposed, including a rapid cooling [1], ultrasonic treatment [2], sol–gel synthesis [3], soft chemistry synthesis [4], microwave solid-state synthesis [5], intercalation of inorganic molecules such as NH 3 ,H 2 O, and CO 2 between layers [6], substitution of V(V) with Mo (VI), Cr(VI) or Mn(IV) [7], substitution of lithium with other monovalent cations such as Na and K [8] and a simple addition of silicon [9]. However, the electrical conductivity of LiV 3 O 8 is extremely low. Therefore, new methods must be proposed to solve the problem for improving the electrochemical properties. In case of V 2 O 5 , two ways have been mainly used to get a high electrical conductivity. One way is a simple addition of the doping metal (Cu, Ag, etc) [12,13], and the other way is intercalation of the polymers (polypyrrole (Ppy) and polyaniline (PANI)) between the layers [14,15]. The strong oxidizing character of V 2 O 5 induces the redox reactions. While the doping metals and polymers are partially oxidized during the process, the V 2 O 5 itself suffers a partial reduction of V 5+ into V 4+ [16]. The forma- tion of V 4+ is correlated with a higher electronic conductivity. Recent study has reported that the electrochemical performance of LiV 3 O 8 could be improved by coating Ppy within the material [17]. To the best of our knowledge, the copper-doped LiV 3 O 8 has not been prepared and also has not been used as a cathode material in lithium- ion batteries. On considering that the transition metal (V) in the LiV 3 O 8 material is in its highest oxidation state, i.e. in its V 5+ valency, LiV 3 O 8 could also be partially reduced by copper powder and would show good electronic conductivity. The purpose of this study is to prepare the copper-doped LiV 3 O 8 powder by a simple addition of the doping metal and to investigate the effect of the copper on the lithium insertion behavior in order to ascertain the validity of our assumption. 2. Experimental 2.1. Synthesis of the samples The stoichiometric mixture of LiOH H 2 O and V 2 O 5 were heated at 500 °C for 16 h, and the solid-state reacted sample was termed LiV 3 O 8 (s) in this paper for convenience. The copper-doped LiV 3 O 8 sample was prepared by mixing the stoichiometric copper powder and LiV 3 O 8 (s) in a proper amount of water. The mixtures were vigorously stirred in distilled water until the copper powders were completely oxidized. The absence of any peak of XRD patterns associated with metallic copper was taken as evidence of complete reaction [12]. Excessive water was then removed at 50 °C. The doped products were termed Cu x LiV 3 O 8 (w) (x = 0, 0.05). It was found that the samples could reabsorb water from humid air on standing, so the composite cathodes would be dried at 100 °C for Materials Letters 62 (2008) 3937–3939 ⁎ Corresponding authors. Yuan is to be contacted at Tel.: +86 22 23498089; fax: +86 22 23502604. Li, Tel.: +86 0592 2187703; fax: +86 0592 2187703. E-mail addresses: lihaixia@xmu.edu.cn (H. Li), yuanht@nankai.edu.cn (H. Yuan). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.05.030 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/matlet