Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-06-18
2003-12-02
Kalafut, Stephen (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C029S623500, C427S377000, C427S402000, C204S192120
Reexamination Certificate
active
06656233
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a negative electrode for use in a lithium secondary cell.
2. Description of the Background Art
A solid secondary cell with a thin lithium film has been proposed. Japanese Patent Laying-Open No. 62-44960 discloses a method for manufacturing such a solid cell. The method includes successively forming a thin film of titanium disulfide as a positive electrode, a thin film of Li
2
O—Al
2
O
3
as an electrolyte, and a thin film of Li as a negative electrode on a substrate placed in an ionized cluster beam evaporation system. Japanese Patent Publication No. 5-48582 discloses an electrolytic material for such a solid cell.
On the other hand, advances have been made in commercialization of lithium secondary cells containing an organic solution of electrolytes. Lithium secondary cells are characterized by having a high-energy output per unit area or per unit weight as compared with other cells. Lithium secondary cells have been developed for practical use as a power source in mobile communications equipment, notebook computers, electric vehicles and the like.
An attempt has been made to use lithium metal for a negative electrode for the purpose of improving the performance of the lithium secondary cell containing an organic solution of electrolytes. Such an attempt, however, involves the risk of a dencdroid growth of the lithium metal during charging and discharging. The dendroid growth may form an internal short-circuit to a positive electrode and finally result in an explosion. As a technique for avoiding the risk, an attempt can be made to form a thin film of a sulfide-based inorganic solid electrolyte on the lithium metal.
The lithium metal, the thin film of the sulfide-based inorganic solid electrolyte, and the source materials therefor, however, are highly reactive to water, so that they cause the problem of degradation when exposed to the air. The above-mentioned publications related to the solid cell, however, do not suggest a technique for independently producing a lithium-containing negative electrode itself. The problem of the degradation described above must be resolved for the production of such a freestanding negative electrode containing lithium and the sulfide-based solid electrolyte.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of producing a negative electrode for a lithium secondary cell, in which lithium metal, a source material for a thin film of a sulfide-based inorganic solid electrolyte, and a negative electrode having the thin film of the inorganic air. solid electrolyte formed thereon can be prevented from being degraded by
The present invention is directed to a method of producing a negative electrode for a lithium secondary cell having a thin film made of an inorganic solid electrolyte. The method includes using a negative electrode base material placed in a closed container and an inorganic solid electrolyte source material placed in a closed container. The negative electrode base material has a surface made of a material selected from the group consisting of lithium metal and lithium alloys. In the method, the negative electrode base material placed in the closed container and the inorganic solid electrolyte source material placed in the closed container are placed into a chamber space, which is substantially inactive to lithium and which is insulated from air and provided adjacent to an apparatus for forming a thin film. In the chamber space, the negative electrode base material and the source material are respectively taken out from the closed containers. Then, the negative electrode base material and the source material taken out are transferred into the apparatus for forming a thin film without being exposed to the air. In the apparatus, the materials are used, and a thin film made of an inorganic solid electrolyte is formed on the negative electrode base material. The negative electrode base material having the thin film formed thereon is then transferred without being exposed to the air into a chamber space, which is substantially inactive to lithium and which is insulated from the air and provided adjacent to the apparatus. In the chamber space, the negative electrode base material having the thin film is placed into a closed container. The negative electrode having the thin film placed in the closed container can be taken out from the chamber into the air without being degraded.
The negative electrode base material for use in the method may be prepared by forming a thin film made of a material selected from the group consisting of lithium metal and lithium alloys on a base material by vapor deposition. The thin film made of the material selected from the group consisting of lithium metal and lithium alloys preferably has a thickness of 20 &mgr;m or less. The thickness of the thin film is typically in the range of 0.1 &mgr;m to 20 &mgr;m, and preferably in the range of 1 &mgr;m to 10 &mgr;m.
The present invention is directed to another method of producing a negative electrode for a lithium secondary cell having a thin film made of an inorganic solid electrolyte. The method includes using a first source material placed in a closed container and a second source material placed in a closed container. The first source material is selected from the group consisting of lithium metal and lithium alloys. The second source material is for use in forming the inorganic solid electrolyte. The first and second source materials respectively placed in the closed containers are placed into a chamber space, which is substantially inactive to lithium and which is insulated from air and provided adjacent to an apparatus for forming a thin film. In the chamber space, the first and second source materials are respectively taken out from the closed containers. Then, the first and second source materials taken out are transferred into the apparatus without being exposed to the air. In the apparatus, the first and second materials are used, and a first thin film made of the first source material and a second thin film made of the second source material are formed on a base material. The base material having the first and second thin films formed thereon is then transferred without being exposed to the air into a chamber space, which is substantially inactive to lithium and which is insulated from the air and provided adjacent to the apparatus. In the chamber space, the base material having the first and second thin films is placed into a closed container. The negative electrode having the thin films placed in the closed container can be taken out from the chamber into the air without being degraded.
In the method, the first thin film may be formed by a vapor deposition method. The first thin film preferably has a thickness of 20 &mgr;m or less. The thickness of the thin film formed is typically in the range of 0.1 &mgr;m to 20 &mgr;m, and preferably in the range of 1 &mgr;m to 10 &mgr;m.
The present invention is directed to a further method of producing a negative electrode for a lithium secondary cell having a thin film made of an inorganic solid electrolyte. In the method, a first source material selected from the group consisting of lithium metal and lithium alloys is placed in a closed container, and the first source material placed in the container is placed into a chamber space, which is substantially inactive to lithium and which is insulated from air and provided adjacent to a first apparatus for forming a thin film. In the chamber space, the first source material is taken out from the closed container. Then, the first source material taken out is transferred into the first apparatus without being exposed to the air. In the first apparatus, the first source material is used, and a first thin film made of the first source material is formed on a base material. The base material having the first thin film formed thereon is transferred from the first apparatus without being exposed to the air into a chamber space, which is
Kugai Hirokazu
Ota Nobuhiro
Yamanaka Shosaku
Alejandro R
Fasse W. F.
Fasse W. G.
Kalafut Stephen
Sumitomo Electric Industries Ltd.
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