Intercalation Processes in Cobalt Substituted Nickel Oxyhydroxides
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INTERCALATION PROCESSES IN COBALT SUBSTITUTED NICKEL OXYHYDROXIDES Claude DELMAS Laboratoire de Chimie du Solide du CNRS and Ecole Nationale Sup6rieure de Chimie et Physique de Bordeaux, 351, cours de la Libdration - 33405 Talence Cedex, France. ABSTRACT Chimie douce reactions (hydrolysis and reduction) from layered oxides : NaNiO 2 , NaxC002 and NaNi l Cox02 lead to numerous oxyhydroxides and hydroxides which differ by -he composition ohf'e intersheet space. According to the experimental conditions of the hydrolysis reaction, the oxyhydroxides can be unhydrated or intercalated with one or two layers of water molecules. From the most hydrated phases, the other ones can be obtained by chemical, thermal and even mechanical treatment. The reduction of Co-substituted nickel oxyhydroxides leads to hydroxides in which nickel and cobalt ions are respectively divalent and trivalent. In order to compensate the excess of positive charge in the (Ni, Co)0 2 sheet, anions (OH-, C0 3 2-, S042-, NO 3D) are inserted in the Van der Waals gap. For the highest anion amounts, well ordered a*-type materials are obtained. Water molecules are simultaneously inserted in the interslab space. Their structure is strongly related to the hydrotalcite one. When the amouit of anions in the intersheet space is not sufficient, interstratified materials are obtained. In this case the (Ni,Co)(OH) 2 slabs are separated by a layer of C0 3 2 - anions and water molecules (a*-type) or by an empty Van der Waals gap (P(Il)-type). The amount of a*-type planes in the structure increases with the cobalt amount. All these materials have been characterized by IR spectroscopy which allows to detect the existence of two types of 0-H bonds (free in cc*-type plane or hydrogen bonded in (IlI)-type plane). INTRODUCTION During the past fifteen years, a very important research effort has been devoted to the study of positive intercalation electrodes for lithium batteries. Among them, the LixMO2 (M = 3d element) type materials seem to constitute one of the most promising group for they lead to high energy density batteries [1,2,3]. Moreover, these materials exhibit high intercalation kinetics and reversibility. The case of homologous materials with sodium as mobile ion is very interesting for the basic point of view as a lot of reversible phase transitions involving sheet gliding occur [4,5]. If the mobile ion is a proton, these materials have been intensively studied in the case of nickel as the 3d element. Hydrogen intercalation in NiOOH: NiOOH + H+ + e-
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Ni(OH)2
occurs in the positive electrode during the discharge of Ni-ed or Ni-H 2 alkaline batteries (known for one century) [6]. Therefore, this reaction can be considered as the first intercalation reaction involved in an electrochemical generator. Nevertheless, only little insight occurred in the study of this reaction front a solid state chemistry viewpoint, as the materials are generally poorly crystallized. Moreover, since their electrochemical activity decreases when the particule size increases, all the ef
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