Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-09-15
2001-01-30
Kalafut, Stephen (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C429S006000, C429S006000, C429S006000, C429S006000, C029S623400
Reexamination Certificate
active
06179884
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the improvement of electrochemical cells, such as solid electrolyte fuel cells, water vapor electrolytic cells, oxygen pumps, NOx decomposition cells or the like.
2. Description of the Prior Art
The solid electrolyte fuel cells, i.e. solid oxide fuel cells (SOFC) , are roughly classified into two categories: a so-called planar type, and a tubular type. In the SOFC of planar type, a stack for power generation is constructed by stacking alternately the so-called separators and generator layers. In Japanese Patent Application Kokai No. 05-054,897, generator layers comprising a fuel electrode (anode) and an air electrode (cathode), respectively, are fabricated, interconnectors are also fabricated, and then, amultilayered body is fabricated by stacking alternately the generator layers and interconnectors with interposition therebetween of a membrane comprising ceramic powder and an organic binder. The layered body is then heat-treated to bond the generator layers with the interconnectors.
Alternatively, in Japanese Patent Application Kokai No. 06-068,885, is described that a green shaped body for an interconnector is stacked on a green shaped body for a distributor on the air-electrode side, and this stacked body is monolithically sintered to bond the interconnector with the distributor. In this method, between both the green shaped bodies is applied a material having a thermal shrinkage behavior extremely different from those of the green shaped bodies, whereby a stress relaxation layer is formed to mitigate stress between the green shaped bodies. This stress relaxation layer disintegrates into fine pieces during shrinking upon firing, whereby the stress is mitigated.
The present inventors have studied the manufacture of electrochemical cells of such a planar type SOFC. A typical shape of the such type electric cells is shown in
FIG. 7
a
that is a schematic cross-sectional view. In
FIG. 7
a
, a support of this electrochemical cell is the conjoint body
41
. This conjoint body
41
is a conjugated body of an air electrode (cathode)
42
with a separator
44
. The air electrode
42
has a planar shape. In the separator
44
, a plurality of narrow, long banks
44
d
and
44
e
are formed on a plate member
44
f
and grooves are formed between the banks
44
d
and
44
e
. With each top face
44
c
of the banks
44
d
and
44
e
, the principal face
42
c
of the air electrode
42
is bonded. Additionally,
44
a
is the bottom face of the separator.
The side face
42
b
of the air electrode
42
is contiguous to the side face
44
b
of the separator
44
without difference in level. An oxidant gas flow passage
43
has a rectangular or square cross-sectional shape. The end portions of the oxidant gas flow passage
43
are open to the end faces of the separator
44
. Additionally,
45
is a joint boundary face. Adense solid electrolyte membrane
19
is formed on the conjoint body
41
. In this instance, the main portion
19
a
of the solid electrolyte membrane
19
is formed on the top face
42
a
of the air electrode
42
. Both sides of the main portion
19
a
are extended to form extended portions
19
b
which cover the side faces
42
b
of the air electrode
42
and further the upper portions of the side faces of the separator
44
. Consequently, the oxidant gas flow passages
43
are kept airtight excepting the openings thereof. A fuel electrode (anode) membrane
20
is formed on the solid electrolyte membrane
19
.
However, it has been found that the following problems are posed in the electrochemical cells of SOFC utilizing such a conjoint body. Namely, when these electrochemical cells are subjected to repetition of a heating-cooling cycle between a high temperature exceeding 1,000° C. during electric generation and room temperature, there may happen the case where the internal resistance of the whole conjoint body of the electrode
42
with the separator
44
is increased, and when things are at the worst, the electrode may be separated from the separator. Particularly, with a heating-cooling cycle test as the above conducted under conditions considerably severer than actual use conditions, it has been found that, in some conjoint bodies, fine cracks are developed from near the joint boundary between the electrode and separator. As shown in
FIG. 7
b
, a stress is most likely to be generated at the portion
48
of the interface between the electrode
42
and the separator
44
.
Alternatively, the same problem as the above has been found also in electrochemical cells other than the SOFC. For example, in the case of high temperature water vapor electrolytic cells, the cells are subjected to the heating- cooling cycle between room temperature and 1,000° C., with starting and stopping of the high temperature water vapor electrolytic cells. Therefore, cells having characteristics which would not be deteriorated even under such severe conditions have been expected.
The task of the present invention is, even when electrochemical cells such as SOFCs or the like are subjected to the repetition of a heating-cooling cycle, for example, from operation at high temperatures exceeding 1,000° C. to temperature fall to room temperature, to prevent the layer separation and crack formation on and around the joint boundary between the separator and electrode so that the increase of the internal electric resistance can be restricted. A further task is to obviate a possibility of developing cracks in the surroundings of the joint boundary of the electrode and separator.
Summary of the Invention
The layered sintered body according to the present invention comprises an electrode and a separator of an electrochemical cell, wherein a plurality of gas flow passages are provided, which is characterized in that a plurality of grooves are provided on the electrode on a side thereof adjoining to the separator, a plurality of grooves are provided on the separator on a side thereof adjoining to the electrode, and each of the gas flow passages is formed by coupling one of said grooves formed on the electrode with the one opposite thereto of the grooves formed on the separator.
Further, the electrochemical cell according to the present invention comprises the above-described layered sintered body, a solid electrolyte membrane provided on an electrode, and another electrode membrane provided on the solid electrolyte membrane, which is characterized in that gas in each gas flow passage is hermetically sealed off from external gases by the separator and solid electrolyte membrane.
When the aforementioned layered sintered bodies or electrochemical cells are manufactured, pug for constituting a green shaped body for an electrode and pug for constituting a green shaped body for a separator are continuously and simultaneously fed into a unitary extrusion die, and extruded from the extrusion die in the form of a layered body consisting of a green shaped body for an electrode and a green shaped body for a separator conjugated with each other, which layered body is then monolithically sintered.
Further when the abovementioned layered sintered bodies or electrochemical cells are manufactured, a shaped body for an electrode is stacked on a shaped body for a separator to provide a layered body, with interposition of a bond material layer between the electrode and separator, in such a fashion that through-holes each corresponding to gas flow passages are formed inside the layered body, and then the layered body is monolithically sintered under pressure.
As regards the conjoint bodies which are supports of the aforementioned planar-type electric cells, the present inventors investigated the reasons for the deterioration of boundary conditions between the electrodes and separators due to the above-described heating-cooling cycle during the generation which causes deterioration of electric characteristics such as internal resistances or the like, and the separation of layers, or the development of cracks under severe conditions. As the result
Ito Shigenori
Kawasaki Shinji
Okumura Kiyoshi
Alejandro Raymond
Kalafut Stephen
NGK Insulators Ltd.
Parkhurst & Wendel L.L.P
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