Li x Co 0.4 Ni 0.3 Mn 0.3 O 2 electrode materials: Electrochemical and structural studies Abdelfattah Mahmoud a , Mayumi Yoshita b , Ismael Saadoune a, *, Joachim Broetz c , Kenjiro Fujimoto b , Shigeru Ito b a LCME, FST Marrakech, University Cadi Ayyad, BP549, Av. A. Khattabi, Marrakech, Morocco b Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, Yamazaki 2461, Noda Chiba 278-8510, Japan c Institute for Materials Science, Darmstadt University of Technology, Petersenstraße 23, 64287 Darmstadt, Germany 1. Introduction Lithium rechargeable batteries are the most advanced power sources for modern portable electronic devices. Since the development of the first commercial lithium rechargeable batter- ies by Sony Corp., a variety of efforts have been undertaken to improve the electrochemical performance of battery materials. Most studies in the field of rechargeable batteries deal with the search for new formulations and structures of active electrode materials or with the optimization of already known compositions [1–4]. LiCoO 2 has served as an archetype electroactive cathode material for rechargeable Li-ion batteries ever since its discovery by Goodenough’s group in 1980 [5–8]. However, LiCoO 2 exhibits a low reversible capacity, a high toxicity and is quite expensive. Indeed, the low reversible capacity of LiCoO 2 was attributed to the dissolution of Co 4+ in the electrolyte at high voltage. Furthermore, cobalt compounds are toxic and less available, thus LiCoO 2 is a relatively high-cost material for lithium batteries [9]. These inherent shortcomings have prevented more widespread use of LiCoO 2 cathode material in rechargeable lithium batteries. There have been increasing demands for development of alternative cathode materials for rechargeable lithium batteries. It has already been suggested by several authors that the dissolution of Co into electrolyte could be suppressed by doping with other transition metal ions LiCoO 2 [10–13]. On the other hand, LiNi 0.5 Mn 0.5 O 2 cathode material has the same structure with LiCoO 2 . The alternating layer arrangement provides a very suitable two- dimensional conduction pathway for the Li ions. This material showed excellent cycleability with a stable discharge capacity of 130 mAh g 1 in the 2.5–4.3 V potential windows [14]. However, the Ni-rich materials have poor thermal stability due to oxygen release from the highly delithiated Li y [Ni 1x M x ]O 2 host structure, which can lead to a severe thermal runaway with explosion [15,16]. One approach to improve the electrochemical and thermal properties of this electrode material and to reduce the above mentioned drawbacks of LiCoO 2 and LiNi 0.5 Mn 0.5 O 2 was to use the solid solution between these two end members, that could be formulated to as Li(Co 12x Ni x Mn x )O 2 with 0  x  ½. Indeed, this solid solution contains the best cathode materials in the Materials Research Bulletin 47 (2012) 1936–1941 A R T I C L E I N F O Article history: Received 11 February 2012 Received in revised form 22 March 2012 Accepted 17 April 2012 Available online 24 April 2012 Keywords: A. Oxides A. Layered compounds B. Electrochemical properties C. Electrochemical measurments C. X-ray diffraction A B S T R A C T LiCo 0.4 Ni 0.3 Mn 0.3 O 2 layered oxide in a member of the LiCo 12x Ni x Mn x O 2 solid solution between LiCoO 2 and LiNi 0.5 Mn 0.5 O 2 . Compositions from this solid solution have attracted much attention and have been extensively studied as promising cathode candidates to replace the most popular LiCoO 2 cathode material used in the commercial lithium-ion batteries (LiBs). LiCo 0.4 Ni 0.3 Mn 0.3 O 2 positive electrode material was prepared via the combustion method followed by a thermal treatment at 900 8C for 12 h. This material was characterized by a high homogeneity and a granular shape. The Rietveld refinement evidenced that the structure of this compound exhibits no Ni/Li disorder revealing that the LiCo 12x Ni x Mn x O 2 system presents the ideal structure for LiBs application when x < 0.4. The electrochemical performances of the LiCo 0.4 Ni 0.3 Mn 0.3 O 2 sample were measured at different current rates in the 2.7–4.5 V potential range. Its discharge capacity reached 178, 161 and 145 mAhg 1 at C/20, 1C and 2C, respectively. Structural changes in LiCo 0.4 Ni 0.3 Mn 0.3 O 2 upon delithiation were studied using ex situ X-ray diffraction. A continuous solid solution with a rhombohedral symmetry was detected in the whole composition range. This structural stability during the cycling combined with the obtained electrochemical features make this material convenient for the LiBs applications. ß 2012 Elsevier Ltd. All rights reserved. * Corresponding author at: University Cadi Ayyad, ECME, FST Marrakech, Av. A. Khattabi, BP 549, Marrakech, Morocco. Tel.: +212 5 24 43 46 88; fax: +212 5 24 43 31 70. E-mail address: saadoune1@yahoo.fr (I. Saadoune). Contents lists available at SciVerse ScienceDirect Materials Research Bulletin jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/mat res b u 0025-5408/$ – see front matter ß 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2012.04.031