In Situ X-Ray Diffraction and In Situ X-Ray Absorption Spectroscopy for Investigation of Intercalation Batteries: Applic
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IN SITU X-RAY DIFFRACTION AND IN SITU X-RAY ABSORPTION SPECTROSCOPY FOR INVESTIGATION OF INTERCALATION BATTERIES: application to the alkaline H+/y-KnO2 system. 3
Lhvy-Clfment , C. Mondolonil, C. Godart2 and R. CortaS . Laboratoire de Physique des Solides de Bellevue, CNRS, 1, place A. Briand, 92195 MEUDON, FRANCE. 2. Laboratoire de M~tallurgie des terres rares, CNRS, 1, place A. Briand 92195 MEUDON, FRANCE. 3. LURE, 91405 ORSAY, FRANCE and Laboratoire d'Electrochimie et Phys. des liquides- Rue Vauquelin- 75005 PARIS, FRANCE. C.
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ABSTRACT
This paper presents applications of in situ X-ray diffraction and absorption techniques to the study of H+/MnO 2 alkaline batteries. The two complementary in situ techniques are described. Investigation of the electrochemical insertion and deinsertion of H+ has been made through its influence on the evolution of the crystallographic structure of 'Y-MnO2 , while investigation of the transfer of e- has been undertaken through the variation of the oxidation state of the manganese during the discharging and charging process of a battery. New insights in the understanding of the mechanisms of proton insertion and charge transfer into -'-MnO2 are discussed.
INTRODUCTION
MnO2 is one of the most popular electrode materials in galvanic cells. Many articles report on synthesis, structure, solid-state properties of various MnO 2 modifications, and on their complex electrochemistry in aqueous electrolytes (1]. Primary cells (saline-Lechanch6 cells and alkaline) are based on the electrochemical insertion of ?. protons into the y-MnO2 variety 3+ Oz2[] 3 (more precisely described by Ruetchi as Mn (l-,-y) Mn ÷y 0(2-4z-y)OH'( 4 z+y)[2]) which is consequently reduced following the simplified reaction:
y-Mnno + xH+ + xe" ---- > HxMnO 2 or MnO 2 .,(OH)x, in which e" represents an electron and x the amount of inserted H+/MnO 2 . A major difference between saline and alkaline type cells concerns the electrolytes used, which are NH4 Cl and concentrated KOH, respectively. Commercial batteries use for the positive electrodes two types of 'y-MnO2 . The EMD type, used in saline and alkaline batteries, is obtained by electrochemical oxidation of manganese (II) while the chemically synthesized CMD type is only used in a mixture with the EMD in some alkaline batteries. It is generally admitted that their crystallographic structure is based on intergrowth domains of two MnO 2 varieties which are the pyrolusite (also designed 0-MnO2 ) and the ramedellite (3]. X-ray diffraction patterns of yMnO 2 , generally poorly crystallized, may look different from one sample to the other without being related to real structural differences. The different types of y-MnO2 are mainly classified by their way of preparation (41. Mechanisms of the insertion of H÷ with the concomitant transfer of e', published only for the EMD type, are still the object of controversial studies. Most of the studies have been concentrated on the saline cells and less on the alkaline types. In the beginning of the discharging, it is Mat. Res.
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