Short communication On the growth of nanostructured iron hydroxy-fluorides for Li-ion batteries B. Guitián a , S. Lascaud b , X.R. Nóvoa a, * , L. Ribeaucourt b , E. Vidal b a ENCOMAT Group, Universidade de Vigo, EEI, Campus Universitario, 36310 Vigo, Spain b EDF R&D, Av. des Renardières, Ecuelles, 77818 Moret-sur-Loing cedex, France highlights graphical abstract  Electrochemically grown nano- structured hydroxyl fluorides.  Impedance-based methodology for in-situ characterization.  Conversion reaction for material preparation and energy recovering. article info Article history: Received 20 October 2012 Received in revised form 24 April 2013 Accepted 28 April 2013 Available online 15 May 2013 Keywords: Conversion reaction Cathode material Rechargeable lithium batteries Iron hydroxyfluoride abstract Lithium ion battery applications such as transportation or renewable energies require cost effective, environmentally friendly and high capacity materials. Conversion reaction with iron based materials at positive electrode is a promising route to reach this target. In this work, iron hydroxyl-fluoride conversion coatings are prepared by an electrochemical way. The structure of the produced coatings is nano-porous with a pore diameter of about 75 nm. An impedance- based methodology is proposed for in-situ characterisation of the conversion coatings during the preparation procedure and enables to optimize the process parameters to get a 3D nano-porous struc- ture. The cycling tests performed in coin-cell versus lithium reference electrode show a promising cycling behaviour for the prepared nano-porous coatings. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction In order to improve the technical and economical perfor- mance of energy storage, most of the research in this field is focused on the development of new electrode materials for batteries. Particularly, lithium-ion batteries have important ca- pacity limitations due to the electrode materials mainly at the positive electrode. An alternative proposed to increase the capacity could be the use of nanostructured materials, such as nanostructured iron fluorides for positive electrode. These ma- terials enable to obtain high specific capacity [1,2] on the order of 700 mAh g 1 . Most papers dedicated to the study of electrode materials are based on the use of powders whose characterization is done a posteriori, on the compacted sample, by X-ray diffraction, XRD, and Scanning electron Microscopy, SEM, examination and com- posite electrodes (including the powders mixed with a binder and a conducting agent spread on a metallic sheet) are made to evaluate the electrochemical properties as battery material. Nevertheless, the approach reported in the present paper is * Corresponding author. Tel.: þ34 986812213. E-mail addresses: rnovoa@uvigo.es, xramonnovoa@gmail.com (X.R. Nóvoa). Contents lists available at SciVerse ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour 0378-7753/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jpowsour.2013.04.145 Journal of Power Sources 241 (2013) 567e571