Method of manufacturing an electrochemical device

#The present invention relates in general to an electrochemical device and a method of manufacturing the same. More particularly, the invention is concerned with an improved method of producing an electrochemical device having a laminar structure which includes an electrochemical cell using a planar solid electrolyte body, and is also concerned with an electrochemical device produced by such an improved method.

#There have been known various electrochemical devices using solid electrolyte, for example, oxygen sensors to detect the oxygen concentration of an exhaust gas emitted from internal combustion engines of automotive vehicles. The typical examples of such oxygen sensors include: an oxygen sensor which comprises a tubular body of oxygen-ion conductive solid electrolyte such as zirconia ceramics, and electrodes of platinum or the like provided on both inner and outer surfaces of the tubular solid electrolyte body, and which operates to determine the oxygen concentration according to the principle of an oxygen concentration cell; an oxygen sensor similar to the above, which incorporates a heater which enables the sensor to operate at a relatively low exhaust gas temperature; and a so-called "lean-burn" sensor suitable for detecting the oxygen concentration of an exhaust gas which is produced at lean air-fuel ratios, i.e., an exhaust gas having a larger oxygen content. Also known in the art are electrochemical sensing and pumping devices for detecting or controling hydrogen, nitrogen, carbon dioxide gas, etc.

#In such electrochemical devices, solid electrolyte materials have been generally used in the form of a tubular body which has an elongate bore closed at its one end. In recent years, however, it has been attempted to replace the tubular solid electrolyte body with a solid electrolyte body of planar shape, as disclosed in U.S. Pat. No. 4,334,974, in view of relatively low productivity and high cost of manufacture of the solid electrolyte bodies of tubular shape, and from the standpoint of easy assembling of parts with the solid electrolyte body. When such planar solid electrolyte bodies are employed, suitable electrodes are disposed in contact with the surfaces of a layer or layers of solid electrolyte, and the electrolyte layers and other parts are assembled into a laminar structure constituting an electrochemical cell or cells.

#The foregoing and other objects, features and advantages of the present invention will become more apparent from reading the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which:

#FIGS. 1 through 4 are exploded perspective views of different forms of a sensing element of an electrochemical device of the invention in the form of an oxygen sensor, respectively;

#FIG. 5 is a schematic elevational view in cross section taken along line V--V of FIG. 4;

#Referring more particularly to the accompanying drawings, several arrangements embodying the concept of the present invention will be described in detail for purposes of illustration.

#There is first shown in an exploded perspective view of FIG. 1 a sensing element in one example of an oxygen-concentration detector which is one embodiment of an electrochemical device of the invention. This sensing element of the oxygen-concentration detector or oxygen sensor includes a planar solid electrolyte layer 2 made of zirconia ceramics containing yttria, or the like, a planar spacer layer 4 and a planar support layer 6 which are made of the same solid electrolyte material as the solid electrolyte layer 2. These planar layers 2, 4 and 6 of solid electrolyte constitute a generally planar or sheet-like solid electrolyte body of laminar structure.

#The spacer layer 4 sandwiched by the solid electrolyte layer 2 and the support layer 6 has an elongate recess 8 formed longitudinally thereof so as to serve as a reference-gas passage 8 in which a reference substance is introduced. A porous reference electrode 10 made of platinum, for example, is disposed on one surface of the support layer 6 so that the reference electrode 10 is exposed to the reference substance (reference gas) such as ambient air introduced in the reference-gas passage 8. On the outer surface of the solid electrolyte layer 2, there is disposed a porous measuring electrode 12 which is made of platinum, for example, so that the measuring electrode 12 is exposed to a measurement gas such as an exhaust gas from an engine of a vehicle.