ARTICLES Local Crystal Structure around Manganese in New Potassium-Based Nanocrystalline Manganese Oxyiodide Seong-Ju Hwang, † Chai-Won Kwon, † Josik Portier, † Guy Campet,* ,† Hyo-Suk Park, ‡ Jin-Ho Choy,* ,‡ Pham V. Huong, § Masahiro Yoshimura, | and Masato Kakihana | Institut de Chimie de la Matie ` re Condense ´ e de Bordeaux (ICMCB) du CNRS, 87 AV. du Dr. A. Schweitzer, 33608 Pessac, France, National Nanohybrid Materials Laboratory, School of Chemistry, Seoul National UniVersity, Seoul 151-747, Korea, Laboratoire de Physico-Chimie Mole ´ culaire, UniVersite ´ Bordeaux I, 351 Cours de la Libe ´ ration, 33405 Talence, France, and Department of Materials Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226, Japan ReceiVed: July 13, 2001; In Final Form: January 17, 2002 A new nanocrystalline potassium-based lithium manganese oxyiodide has been prepared by using Chimie Douce route at room temperature. According to the electrochemical measurements, this nanocrystalline sample shows a large initial capacity up to ∼340 mAh/g at a constant current density of 0.2 mA/cm 2 , which is much larger than that of sodium-based homologue. The X-ray diffraction analysis demonstrates that the amorphous character of the nanocrystalline compounds is maintained before and after chemical lithiation reaction. The local crystal structure around manganese in these materials has been determined by performing the combinative micro-Raman and X-ray absorption spectroscopy. From the Mn K-edge X-ray absorption near-edge structure and micro-Raman results, it becomes certain that manganese ions are stabilized in the rhombohedral layered lattice consisting of edge-shared MnO 6 octahedra, and the crystal symmetry is changed into a monoclinic symmetry upon reaction with n-BuLi. The Mn K-edge extended X-ray fine structure analysis reveals that the structural distortion caused by lithiation process is less significant for these nanocrystalline compounds than for the spinel lithium manganate. In this context, the great discharge capacity of the nanocrystalline materials is attributable for the pillaring effect of larger alkali metal ion than lithium ion, providing an expanded interlayer space available for Li insertion. In addition, the I L I -edge X-ray absorption near-edge structure results presented here make it clear that iodine is stabilized as iodate species on the grain boundary or the surface of the nanocrystalline manganese oxyiodide, which helps to maintain the nanocrystalline nature of the present materials before and after Li insertion. Introduction Recently, special attention has been paid for lithium man- ganese oxides as promising cathode materials for lithium rechargeable batteries, which is due to the low toxicity, rich abundance, and low price of manganese. 1 In this context, various types of lithium manganates have been explored for the purpose of developing new cathode materials with better electrochemical performance. 2-4 However, most of lithium manganates experi- ence a common structural modification to a spinel-type cation ordering in the course of electrochemical cycling. 5,6 This thermodynamically stable spinel phase has been well-known to suffer from capacity fading during repeated charge-discharge cycling. 1 The capacity loss of this cathode material is closely related to the structural transition from cubic spinel to tetragonal one, leading to a structural breakdown and to a formation of electronically isolated zones. 7 In fact, this sort of problem originating from the phase transition is considered to be more or less inevitable for well-crystallized lithium metal oxides. Such a speculation gives an impetus to develop amorphous phases as alternative cathode materials, since this type of compounds would be much more tolerable for the repeated Li insertion- deinsertion process. For example, very recently we have found that nanocrystalline spinel compound exhibits an enhanced electrochemical performance for 3 V region corresponding to Li insertion into 16c site in the spinel phase, which would be understood by the grafting mechanism of lithium on the surface of nanocrystalline material. 8 In addition, there have been some reports on nanocrystalline lithium manganese oxides showing superior electrochemical properties over well-crystalline homo- logues. 9-12 Among these nanocrystalline materials, sodium- based manganese oxyiodides possess a quite large discharge capacity and the best cyclability, and moreover their electro- chemical performances can be improved by ball-milling pro- cess. 9 On the other hand, Whittingham, M. S. et al. reported * To whom correspondence should be addressed.Guy Campet: Phone: +33-5-56-84-62-97. Fax: +33-5-56-84-27-61. E-mail: campet@ icmcb.u-bordeaux.fr. Jin-Ho Choy: Phone: +82-2-880-6658. Fax: +82-2-872-9864. E-mail: jhchoy@plaza.snu.ac.kr. † Institut de Chimie de la Matie `re Condense ´e de Bordeaux (ICMCB) du CNRS. ‡ Seoul National University. § Universite ´ Bordeaux I. | Tokyo Institute of Technology. 4053 J. Phys. Chem. B 2002, 106, 4053-4060 10.1021/jp012704g CCC: $22.00 © 2002 American Chemical Society Published on Web 03/30/2002