Oxygen Gettering Effect During the Reactive Evaporation of Manganese Oxide Films
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Oxygen gettering effect during the reactive evaporation of manganese oxide films Masaaki Isai,a) Katsuma Yamaguchi, Haruhiko Iyoda, and Hiroshi Fujiyasu Department of Electrical and Electronic Engineering, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8561, Shizuoka, Japan
Yasumitsu Ito Miyakoda Electronics Technical Center, Suzuki Motor Corporation, Shinmiyakoda 1-1-2, Hamamatsu 431-2103, Shizuoka, Japan (Received 6 December 1997; accepted 19 October 1998)
Manganese oxide films for lithium secondary batteries were prepared using a reactive evaporation method. Mn was evaporated from a molybdenum boat by resistive heating and deposited on a glass slide under oxygen atmosphere. These films were examined with x-ray photoelectron spectroscopy (XPS) and x-ray diffraction. The Mn oxide films with a wide valency of Mn were prepared in this study. A rapid change of the back pressure was found as the deposition of Mn was started. This implies that Mn atoms start to react with O2 . This means that in situ detection of reactive evaporation process can be utilized.
I. INTRODUCTION
There has been considerable interest in electric vehicles operating with lithium secondary batteries. There are a lot of potential candidate materials for secondary batteries.1 A combination of manganese (Mn) oxide and lithium (Li) was the focus of this study as the positive and negative electrodes, respectively. Mn oxides are one of the best materials for the positive electrode in the Li secondary batteries.2 Mn is inexpensive because it is found in abundance on earth. The operating voltage of 3–4 V is obtained with this material. But, almost all companies have been using cobalt (Co) or nickel (Ni) oxides for the positive electrode. The positive electrode is composed of an oxide film on the metal electrode. Almost all the oxide powders for positive electrodes are prepared by the sintering method.3–11 Then they are mixed with some binders and applied to the metal electrode. This application method makes the electric contact insufficient. So some ingredients must be added to improve the electric conductivity. This problem could be overcome by using the vacuum deposition process proposed in this paper. Lithium atoms are very active in air and in water vapor. Li secondary batteries should be fabricated in high quality vacuum from the beginning to the end of the fabrication process. From these properties of Li atoms, Mn oxide films, which involve Li atoms, should be carefully prepared in vacuum. One of the best ways is the all solid state batteries which are built up in vacuum at one batch. a)
e-mail: [email protected] J. Mater. Res., Vol. 14, No. 4, Apr 1999
http://journals.cambridge.org
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The Mn oxide films were prepared by the so-called reactive evaporation method.12–14 A rapid change of the vacuum pressure was found as the deposition of Mn was started. This implies that Mn atoms start to react with O2 atmosphere. The purpose of the present work is to clarify the corre
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