A FLAT TYPED SEALED BATTERY WITH HERMETIC SEALING STRUCTURE

Abstract: A flat disc type sealed battery comprises a battery vessel (5) having a bottom wall (5a) with an electrolyte charging opening (12) formed in the central portion thereof, a battery lid member (6) for covering the upper opening of the battery vessel (5). Power generating components are enclosed by sealing the battery vessel (5) and battery lid member (6), and a first sealing member (13) is provided for sealing the electrolyte charging opening (12) after the electrolyte is charged into the battery vessel (5), and a second sealing member (14) is provided for covering the aperture in the side of the lower edge portion of the electrolyte charging opening (12), and the outer peripheral portion of the second sealing member (14) is welded to the bottom wall (5a) of the battery vessel (5) to seal the battery vessel perfectly.

Description: The present invention relates to a flat sealed type battery with an electrolyte charging aperture formed in the central portion of a bottom wall of a battery vessel. In recent years, in various fields there have been used lithium batteries having little self-discharge and a long life with a progress of electronic apparatuses. Therefore, there has been developed a lithium-oxyhalide battery such as a lithium thionyl chloride battery adopting so called a hermetic sealing structure of a cylindrical type with a battery lid made of metal-glass-metal, which is used as a power source for memory back up of C-MOS RAM. Since such a battery has a structure with high sealing function and has a long life of more than ten years, the demand for such a lithium oxyhalide battery is rapidly increased. However, in the market, not only the above mentioned cylindrical type batteries for memory back up but also a small and thinned type batteries for memory back up are demanded because of demand for reduction of consumption of current of IC and for miniaturization and lightening of the apparatuses in size and weight. Although there has been commercialized a flat type lithium battery such as a lithium manganese dioxide battery or lithium graphite fluoride battery in the prior art, the sealing structure of such a battery is made in so called a crimp seal method that there is provided gasket made of plastic resin materials between an opening end portion of a positive electrode can and the outer peripheral portion of a negative electrode can so that the opening end portion of the positive electrode can is fastened inwardly so as to seal the battery vessel (see the Japanese Patent Laid Open Sho 56-167274 for example). Therefore, there is limitation of a period in which the battery is available with a sealing ability, and the battery is available for at most 5 to 7 years and it can not possibly be used for more than ten years. Accordingly, though a flat type sealed battery with high sealing function employing a hermetic seal is demanded by users, the demand of the users is not yet realized due to the difficulty of the sealing techniques after charging the electrolyte. That is to say, in the cylindrical type battery, the size and volume of the battery is large and the total height of the battery is at least more than 25 mm and since the sealing process is performed on the top end portion of a pipe used as an electrolyte charging entrance after the charge of the electrolyte (see the Japanese Patent Laid Open Sho 62-160660 for example), therefore, there can be formed a distance of at least more than 5 mm between the surface of the electrolyte and the sealed portion in the battery vessel, so that the heat applied at the time of the welding for sealing affects a little on the electrolyte. However, in the flat type battery with a total height of the battery of at most 10 mm, since the distance between the surface of the electrolyte and the welded portion for sealing is merely almost 1 to 2 mm, the electrolyte is vaporized due to the heat applied at the time of welding for sealing so that the vaporized gas is spurted out from the inside of the battery, which flies to the welded portion for sealing, so that there occurs a pin hole at the welded portion, resulting in that a perfect sealing structure can not be realized. In the conventional flat type battery, if an electrolyte charging entrance is formed at the edge portion of the battery lid, the welding portion thereof is so near to a glass layer that the glass layer is easy to be broken due to the heat of the welding, and therefore, as shown in Fig. 1, it is attempted that, there is formed a hole at the central portion of the bottom wall 5a of the battery vessel 5 so as to use as an electrolyte charging entrance 12. After the electrolyte is charged into the battery vessel through the electrolyte charging entrance 12, the state of the battery is reversed up and down to the state of the battery shown in Fig. 1 at least from the time of charging the electrolyte and the electrolyte charging entrance 12 is covered with a sealing plate 14 and the outer peripheral portion of the sealing plate 14 is welded with the bottom wall 5a of the battery vessel 5. However, as described above, since the distance between the welded portion for sealing and the surface of the electrolyte is so short that the electrolyte is vaporized due to the heat of the welding and the vaporized gas goes out to the welded portion, resulting in that the welding is prevented or there occurs a pin hole at the welded portion so as to cause a damage of the sealing structure. US-A 4 398 346 reveals a battery cell having a charging opening in the upper lid. After filling of the cell, the opening is first plugged with a teflon plug, then sealed by a stainless steel cap which is finally welded to the lid. The present invention has been made in order to solve the problem mentioned above and has its object to provide a flat type sealed battery with a high sealing function which can be used for more than ten years, solving difficulties of the sealing technique when producing a flat type sealed battery adopting a hermetic seal as described above, thereby obtaining a good welding of a battery vessel. In order to accomplish the object mentioned above, a flat disc type sealed battery comprises the features of claim 1. Further embodiments of the invention can be found in the dependent claims. Fig. 1 is a sectional view showing a conventional flat type sealed battery, Fig. 2 is a sectional view showing a first embodiment of a flat type sealed battery according to the present invention, Fig. 3(a) is an enlarged sectional view showing an essential part of the battery shown in Fig. 2, Fig. 3(b) is an exploded view of Fig. 3(a), Fig. 4(a) is a sectional view showing a second embodiment of a flat type sealed battery according to the present invention, Fig. 4(b) is an enlarged sectional view showing an essential part A of the battery shown in Fig. 4(a), Fig. 5(a) is a sectional view showing a third embodiment of a flat type sealed battery according to the present invention, Fig. 5(b) is an enlarged sectional view showing an essential part A of the battery shown in Fig. 5(a), Fig. 6(a) is a sectional view showing a fourth embodiment of a flat type sealed battery according to the present invention, Fig. 6(b) is an enlarged sectional view showing an essential part A of the battery shown in Fig. 6(a), Figs. 7 and 8 are sectional views showing the other examples of the first sealing member for use in the flat type sealed battery according to the present invention, Fig. 9 is a sectional view showing a ninth embodiment of a flat type sealed battery according to the present invention, Fig. 10(a) is an enlarged sectional view showing an essential part of the battery shown in Fig. 9, Fig. 10(b) is an exploded view of Fig. 10(a), Fig. 11(a) is a sectional view showing a tenth embodiment of a flat type sealed battery according to the present invention, Fig. 11(b) is an enlarged sectional view showing an essential part A of the battery shown in Fig. 11(a), Fig. 12(a) is a sectional view showing a eleventh embodiment of a flat type sealed battery according to the present invention, Fig. 12(b) is an enlarged sectional view showing an essential part A of the battery shown in Fig. 12(a), Fig. 13(a) is a sectional view showing a twelfth embodiment of a flat type sealed battery according to the present invention, Fig. 13(b) is an enlarged sectional view showing an essential part A of the battery shown in Fig. 13(a), Fig. 14(a) is a sectional view showing a thirteenth embodiment of a flat type sealed battery according to the present invention, Fig. 14(b) is an enlarged sectional view showing an essential part A of the battery shown in Fig. 14(a), Fig. 15 is a schematic bottom plan view of the battery vessel, and Fig. 16 is a sectional view cutting along the line A-A shown in Fig. 15. Before the description proceeds, it is noted that since the basic structure of the battery is similar to that of the conventional battery explained with reference to Fig. 1, like parts are designated by the same reference numerals and the explanation of details thereof is herein omitted for the brevity. In the central portion of a bottom wall 5a of a battery vessel 5 is formed an electrolyte charging opening 12 of a cylindrical shape or taper cylindrical shape in which a first sealing member 13 of generally spherical shape is provided for sealing the battery vessel after charging the electrolyte in the battery vessel and a second sealing member 14 of disc plate is provided for sealing the lower entrance aperture of the electrolyte charging opening 12 and the outer peripheral portion of the upper surface of the second sealing member 14 is welded to the bottom wall 5a of the battery vessel 5 so as to cover the lower aperture of the opening 12, thereby sealing the battery vessel. Further described in detail, in the embodiments of the present invention, since the first sealing member 13 is inserted in the electrolyte charging opening 12 by press fitting to the inner surface of the surrounding wall of the cylindrical or taper cylindrical shaped opening 12, the circumference wall of the electrolyte charging opening 12 is expanded by the press fitting insertion of the first sealing member 13 so that the reactive stress for recovering the peripheral wall of the electrolyte charging opening 12 is applied to the contacted portion of the first sealing member 13, thereby enhancement of the sealing function between the peripheral wall of the electrolyte charging opening 12 and the first sealing member 13. Therefore, when the outer peripheral portion of the second sealing member 14 is welded to the bottom wall 5a of the battery vessel 5 so as to seal the battery vessel, the evaporated gas of the electrolyte does not go out to the welded portion so that the welding of the second sealing member 14 can be performed without any pinhole in the welded portion so that the electrolyte charging opening 12 is perfectly sealed, thereby obtaining a battery with high sealed structure. Although, in the embodiments mentioned below, the explanation is made about a flat type sealed battery of a lithium thionyl chloride group, the present invention is not limited to this. EXAMPLE 1 (comparative) Figs. 2 and 3 show of a flat disc type sealed battery wherein in the sectional views, if the drawing becomes complicated when the outline of the portion positioning in the back side than the section is drawn, the outline of the back portion is omitted. In the example 1, the first sealing member 13 of generally spherical shape and the second sealing member 14 of disc plate are respectively provided separately, which is similar to those in the examples 2 to 8. Referring to the schematic constitution of the flat disc type sealed battery, reference numeral 1 denotes a negative electrode made of lithium, reference numeral 2 denotes a positive electrode made of amorphous carbon porous mold, and reference numeral 3 denotes a separator member made of glass fiber non-woven fabric for separating the negative electrode 1 from the positive electrode 2. Reference numeral 4 denotes electrolyte, reference numeral 5 denotes a battery vessel made of stainless steel. Reference numeral 6 denotes a battery lid member which comprises a ring shaped body member 7 made of stainless steel, a ring shaped insulating layer 8 made of glass and a positive electrode terminal member 9 made of stainless steel, wherein the outer peripheral portion of the body member 7 is welded to the upper end portion of the circumference wall of the top opening of the battery vessel 5. Reference numeral 10 denotes a charge collecting member made of stainless steel mesh which is spot-welded to the bottom surface of the positive electrode terminal 9. Reference numeral 11 denotes an insulating member made of glass fiber non-woven fabric for insulating the positive electrode 2 and the positive electrode charge collector 10 from the body member 7 of the battery lid 6. Reference numeral 12 denotes an electrolyte charging opening of a cylindrical shape with its top end portion 12a projected to the inside of the battery, which is formed in the central portion of the bottom wall 5a of the battery vessel 5 (see Fig. 3). Reference numeral 13 denotes a first sealing member of generally spherical form which is inserted by press fitting in the electrolyte charging opening 12 after the electrolyte 4 is charged in the battery vessel through the electrolyte charging opening 12. Reference numeral 14 denotes a second sealing member of disc plate made of stainless steel of which the central portion covers the entrance aperture at the side of the lower edge 12b of the electrolyte charging opening 12 and the outer peripheral portion of the second sealing member 14 is welded to the bottom wall 5a of the battery vessel 5 as shown in Fig. 3(a). The battery is a small and thinned flat disc type with an outer diameter of 33 mm and total height of 6.5 mm. With detailed description of the essential members of the battery, the negative electrode 1 is made in a manner that a lithium sheet molded in a ring disc shape is pressed onto the inner surface of the bottom wall 5a of the battery vessel 5 and is made of only lithium material which is negative electrode active material. The positive electrode 2 is made of porous mold of substantially including amorphous carbon consisting of mainly acetylene black and additive graphite and polytetrafluoroethylene added, which is so called amorphous carbon porous mold. The electrolyte 4 is made of thionyl chloride solution consisting of thionyl chloride having aluminum lithium tetrachloride of 1 mol/lit. solved, wherein the thionyl chloride is the solvent of the electrolyte and is also used as the positive electrode active material. As is apparent from the fact that the thionyl chloride is used as the positive electrode active material, the positive electrode 2 is not reacted but it is disposed for providing the place for the reaction between the thionyl chloride as the positive electrode active material and the lithium ion which is ionized and solved from the negative electrode 1 into the electrolyte 4. The battery vessel 5 is formed in a flat disc vessel of stainless steel plate of 0.5 mm thick, with an outer diameter of 33 mm and total height of 6 mm, wherein in the central portion of the bottom wall 5a is formed a cylindrical electrolyte charging opening 12 whose surrounding wall has a top end portion 12a projected inwardly having an inner diameter of 2.1 mm and height of generally 1.5 mm. The cylindrical electrolyte charging opening 12 means that, when the electrolyte 4 is charged into the battery vessel, the entrance aperture through which the electrolyte is charged is formed to be cylindrical shape. The battery lid 6 comprises the lid body member 7 made of stainless steel, the ring shaped insulating layer 8 made of glass and the positive electrode terminal 9 made of stainless steel, wherein the outer surface of the insulating layer 8 is welded to the inner surface of the lid body 7 and the inner surface of the insulating layer 8 is welded to the outer surface of the positive electrode terminal 9 so as to hold the hermetic seal structure formed of metal-glass-metal, and moreover, the outer peripheral of the lid body member 7 is welded to the upper end portion of the circumference wall of the upper opening of the battery vessel 5 as mentioned above, thereby obtaining the perfect sealing structure of the battery. In this example, the first sealing member 13 has a spherical body of 2.3 mm diameter made of polytetrafluoroethylene and the diameter of the first sealing member 13 is made a little larger than the inner diameter of the electrolyte charging opening 12 so that the first sealing member 13 is inserted in the electrolyte charging opening 12 by press fitting to the surrounding wall of the opening 12 after the electrolyte is charged into the battery vessel. Therefore, the reactive stress of the surrounding wall member of the electrolyte charging opening 12 is applied to the contacted portion of the first sealing member 13 so that the contact ability is enhanced between the first sealing member 13 and the surrounding wall of the electrolyte charging opening 12, whereby the electrolyte charging opening 12 is sealed by the first sealing member 13 at least during the period until the second sealing member 14 is welded to the bottom wall 5a so as to seal the battery vessel. The second sealing member 14 is made of stainless steel plate of a disc shape of 0.3 mm thick and 5 mm diameter whose central portion covers the entrance aperture at the side of the bottom end 12b of the electrolyte charging opening 12 and the peripheral portion of the second sealing member 14 is welded to the bottom wall 5a of the battery vessel 5. That is to say, the electrolyte charging opening 12 is temporarily sealed by the press fitting insertion of the first sealing member 13 therein and is perfectly sealed by welding the outer peripheral portion of the second sealing member 14 to the bottom wall 5a of the battery vessel 5. The flat disc type sealed battery as mentioned above is produced in a manner as follows. First, the electrolyte charging opening 12 is formed in the central portion of the bottom wall 5a of the battery vessel 5 as described above. Subsequently, the charge collecting member 10 on the positive electrode 2 is spot-welded to the lower surface of the positive electrode terminal 9 of the lid member 6 and the insulating member 11 is installed between the lid body 7 and the charge collecting member 10. Next, the ring shaped lithium sheet is pressed to be bonded onto the inner surface of the bottom wall 5a of the battery vessel 5 to form the negative electrode 1 on which the separator member 3 is disposed. Subsequently, the positive electrode 2 is installed on the separator member 3 and the battery lid member 6 is fitted in the peripheral edge wall of the upper opening of the battery vessel 5 so that the outer peripheral portion of the lid body 7 of the battery lid 6 is welded to the peripheral edge wall of the upper opening of the battery vessel 5 by using a carbonic acid gas laser. At the time of sealing by welding as mentioned above, the output power of the carbonic acid gas laser is 700W and the welding speed is 60mm/sec. Subsequently, the battery under assembling is reversed up and down to the state shown in Fig. 2 and after the electrolyte is charged into the battery vessel 5 through the electrolyte charging opening 12 by a vacuum charging method, the first sealing member 13 is inserted by press fitting into the electrolyte charging opening 12 and the entrance aperture surrounded by the base edge portion 12b of the electrolyte charging opening 12 is covered by the second sealing member 14 and after the second sealing member 14 is spot-welded to be fixed to the bottom wall 5a of the battery vessel 5, the outer peripheral portion of the second sealing member 14 is welded to the bottom wall 5a of the battery vessel 5 by the carbonic acid gas laser so as to seal the opening 12 perfectly, thereby obtaining a desired battery with a sealed structure. At this time, the welding is performed under the condition that the output power of the laser is 400W and the welding speed is 20mm/sec. EXAMPLE 2 (comparative) Fig. 4 shows a second flat disc type sealed battery. In this example, the difference point from the first example is in that the shape of the electrolyte charging opening 12 is formed to be taper cylindrical shape and the other structures are generally similar to those in the example 1. Therefore, the explanation is made only about the electrolyte charging opening 12 and the reference portions associated therewith. The battery vessel 5 is made of stainless steel plate of 0.5 mm thick, having an outer diameter of 33 mm and total height of 6 mm. The electrolyte charging opening 12 of a taper cylindrical shape is formed in the central portion of the bottom wall 5a of the battery vessel 5 having the top edge portion 12a of the opening 12 projected toward the inside of the battery as shown in Fig. 4(b). The taper cylindrical shape of the electrolyte charging opening 12 means that the space of the aperture for charging the electrolyte into the battery vessel is formed to be a taper cylindrical shape. In the electrolyte charging opening 12, the maximum inner diameter surrounded by the base edge portion 12b of the bottom wall 5a is made 3 mm, and the minimum inner diameter surrounded by the top end portion 12a of the bottom wall 5a is made 2.1 mm. After the electrolyte is charged into the battery vessel by a vacuum charging method through the electrolyte charging opening 12, the first spherical sealing member 13 of 2.3 mm diameter, which is made of polytetrafluoroethylene, is inserted in the electrolyte charging opening 12 by press fitting to the end portion 12a of the surrounding wall thereof. Because of the press fitting insertion of the first sealing member 13 of a spherical shape with a diameter slightly larger than the minimum inner diameter of the electrolyte charging opening 12, the reactive stress of the surrounding wall of the bottom wall 5a of the electrolyte charging opening 12 is applied to the first sealing member 13 due to the press fitting insertion of the sealing member 13 so that the fitting ability is enhanced between the first sealing member 13 and the surrounding wall of the electrolyte charging opening 12. Therefore, since the electrolyte charging opening 12 is sealed by the first sealing member 13 at least during the period until the second sealing member 14 is completely welded to the bottom wall 5a of the battery vessel 5, it is avoided that, at the time of welding the second sealing member 14, the evaporated gas of the electrolyte goes out to the welding portion to prevent the welding due to the occurrence of pinholes in the welding portion. The second sealing member 14 of a disc shape is made of stainless steel plate of 0.3 mm thick and 5 mm diameter, and the central portion thereof covers the entrance aperture of the electrolyte charging opening 12 under the condition that the outer peripheral portion thereof is welded to the bottom wall 5a of the battery vessel 5 by the carbonic acid gas laser. The condition of the welding of the second sealing member 14 is similar to that in the first example. EXAMPLE 3 (comparative) Fig. 5 shows a third a flat disc type sealed battery. In the example 3, the central portion of the bottom wall 5a of the battery vessel 5 is projected toward the inside of the battery so as to form a convex portion 5a₁ (i.e., seeing from the outer surface of the bottom wall of the battery, the central portion thereof is recessed inwardly so as to form a concave portion 5a₁) and the electrolyte charging opening 12 of a cylindrical shape is formed in the central portion of the convex portion 5a₁. After the electrolyte is charged into the battery vessel, the first sealing member 13 of generally spherical shape is inserted in the cylindrical electrolyte charging opening 12 by press fitting as described in the example 1. The second sealing member 14 is attached in the concave portion 5a₁ from the outside of the bottom wall 5a so that the level of the bottom surface of the second sealing member 14 is made generally equal to that of the bottom surface of the main bottom wall 5a, whereby the increment of the total height of the battery due to providing the second sealing member 14 can be reduced. Other structures of the example 3 are similar to those in the example 1. EXAMPLE 4 (comparative) Fig. 6 shows a fourth flat disc type sealed battery , which is a combination of the examples 2 and 3. In the example 4, the central portion of the bottom wall 5a of the battery vessel 5 is projected toward the inside of the battery so as to form a convex portion 5a₁ (i.e., seeing from the outer surface of the bottom wall of the battery, the central portion thereof is recessed inwardly so as to form a concave portion 5a₁) and the electrolyte charging opening 12 of a taper cylindrical shape is formed in the central portion of the convex portion 5a₁. After the electrolyte is charged into the battery vessel, the first sealing member 13 is inserted in the taper cylindrical electrolyte charging opening 12 by press fitting as described in the example 2. The second sealing member 14 is fitted in the concave portion 5a₁ from the outside of the bottom wall 5a so that the level of the bottom surface of the second sealing member 14 is made generally equal to that of the bottom surface of the main bottom wall 5a, so that the increment of the total height of the battery due to providing the second sealing member 14 can be reduced. Other structures of the fourth example are similar to those of the example 3. EXAMPLEs 5 to 8 (comparative) In the examples 5 to 8, a spherical member made of stainless steel is used as the first sealing member 13. In the fifth example, as the first sealing member 13, there is used a spherical member made of stainless steel with a diameter of 2.3 mm and the other structures are similar to those in the example 1. In the example 6, as the first sealing member 13, there is used a spherical member made of stainless steel with a diameter of 2.3 mm and the other structures are similar to those in the example 2. In the example 7, as the first sealing member 13, there is used a spherical member made of stainless steel with a diameter of 2.3 mm and the other structures are similar to those in the example 3. In the example 8, as the first sealing member 13, there is used a spherical member made of stainless steel with a diameter of 2.3 mm and the other structures are similar to those in the example 4. In these examples 1 to 8, the outer peripheral portion of the second sealing member 14 is welded to the bottom wall 5a of the battery vessel 5 by the carbonic acid gas laser under the same condition as that in the example 1, that is, the output power of the laser is 400W and the welding speed is 20 mm/sec. EXAMPLE 9 Figs. 9 and 10 show a first embodiment of a flat disc type sealed battery according to the present invention, wherein the first sealing member 13 and the second sealing member 14 are connected as one sealing member, which is similar to those in the examples 10 to 13. And since other main structures thereof and the method for producing the battery are similar to those in the examples 1 to 8, the explanation thereof is omitted. The first sealing member 13 with an oval shape comprises a top portion 13a of a spherical shape having the diameter gradually increasing to the maximum at the middle portion thereof and decreasing to the lower portion thereof and the maximum diameter is made 2.3 mm, which is slightly larger than the inner diameter of the electrolyte charging opening 12, so that the first sealing member 13 is inserted in the electrolyte charging opening 12 by press fitting as described above so as to seal the electrolyte charging opening 12. However, the shape of the first sealing member 13 is not limited to the oval form and the other types may be used as shown in Figs. 7 and 8. The second sealing member 14 which is the base plate connected to the first sealing member 13 as one body has a diameter of 5 mm and a thickness of 0.3 mm, so that the sealing plate 14 covers the entrance of the opening 12 at the side of the base edge portion 12b and the outer peripheral portion of the sealing plate 14 is welded to the bottom wall 5a as described above. EXAMPLE 10 Fig. 11 shows a second embodiment of a flat disc type sealed battery according to the present invention. In this example, the difference point from the example 9 is in that the electrolyte charging opening 12 is formed to be taper cylindrical shape and the first sealing member 13 is made column shaped with its top portion 13a formed to be coniform and the other structures are generally similar to those in the ninth example as shown in Fig. 9. Therefore, the explanation is made only about the electrolyte charging opening 12 and the reference portions associated therewith. The battery vessel 5 is made of stainless steel plate of 0.5 mm thick, having an outer diameter of 33 mm and total height of 6 mm. The electrolyte charging opening 12 of a taper cylindrical shape is formed in the central portion of the bottom wall 5a of the battery vessel 5 having its top edge portion 12a of the opening 12 projected toward the inside of the battery as shown in Fig. 11(b). The taper cylindrical shape of the electrolyte charging opening 12 means that the space of the aperture for charging the electrolyte into the battery vessel is formed to be a taper cylindrical shape. In the electrolyte charging opening 12, the maximum inner diameter of the entrance aperture surrounded by the base edge portion 12b of the bottom wall 5a is made 3 mm, and the minimum inner diameter surrounded by the top end portion 12a of the bottom wall 5a is made 2.1 mm. After the electrolyte is charged into the battery vessel by a vacuum charging method through the electrolyte charging opening 12, the taper column sealing member 13 with a maximum diameter of 2.3 mm is inserted in the electrolyte charging opening 12 by press fitting to the end portion 12a of the surrounding wall thereof. Because of the press fitting insertion of the taper column sealing member 13 having a diameter slightly larger than the minimum inner diameter of the electrolyte charging opening 12, the reactive stress of the surrounding wall of the bottom wall 5a of the electrolyte charging opening 12 is applied to the taper column sealing member 13 due to the press fitting insertion of the sealing member 13 so that the fitting ability between the taper column sealing member 13 and the surrounding wall of the electrolyte charging opening 12 is enhanced. Therefore, since the electrolyte charging opening 12 is sealed by the taper column sealing member 13 at least during the period until the base sealing plate 14 is completely welded to the bottom wall 5a of the battery vessel 5, it is avoided that, at the time of welding the base sealing plate 14, the gas of the evaporated electrolyte goes out to the welding portion so as to prevent the welding due to the occurrence of pinholes in the welding portion. The base sealing plate 14 of disc shape is made of stainless steel plate of 0.3 mm thick and 5 mm diameter, and the center portion thereof covers the entrance aperture of the electrolyte charging opening 12 under the condition that the outer peripheral portion thereof is welded to the bottom wall 5a of the battery vessel 5 by the carbonic acid gas laser. The condition of the welding of the base sealing plate 14 is similar to that in the ninth example, i.e., the output power of the laser is 400W and the welding speed is 20 mm/sec. EXAMPLE 11 Fig. 12 shows a third embodiment of a flat disc type sealed battery according to the present invention, which is a combination of the examples 3 and 9. And since other main structures thereof and the method for producing the battery are similar to those in the examples 3 and 9, the explanation thereof is omitted. EXAMPLE 12 Fig. 13 shows a fourth embodiment of a flat disc type sealed battery according to the present invention, which is a combination of the examples 4 and 10. And since other main structures thereof and the method for producing the battery are similar to those in the examples 4 and 10, the explanation thereof is omitted. EXAMPLE 13 Fig. 14 shows a fifth embodiment of a flat disc type sealed battery according to the present invention. In this example, the difference point from the example 12 is in that the electrolyte charging opening 12 of a taper cylindrical shape is formed in the central portion of the bottom wall 5a of the battery vessel 5 having a portion 5a₂ bent vertically to form a small cylindrical shape and its edge portion 12a of the opening 12 projected downwardly (toward the outside of the battery) as shown in Fig. 14(b). In this modification, the corner edge 12a₁ of the edge portion 12a is welded to the upper surface of the second sealing plate 14 with the other corner 12a₂ pressed to the cylindrical surface of the first sealing member 13. And since other main structures thereof and the method for producing the battery are similar to those in the example 12, the explanation thereof is omitted. COMPARISON Next, the table 1 shows the results of occurrence of the inferior welding in the batteries due to the occurrence of the pinholes when the second sealing member 14 is welded by the carbonic acid gas laser, comparing the examples of the battery according to the present invention with the comparative example of the conventional battery shown in Fig. 1. BATTERY NUMBER OF BATTERIES HAVING INFERIOR WELDING CAUSED EXAMPLE 1 0 / 20 EXAMPLE 2 0 / 20 EXAMPLE 3 0 / 20 EXAMPLE 4 0 / 20 EXAMPLE 5 0 / 20 EXAMPLE 6 0 / 20 EXAMPLE 7 0 / 20 EXAMPLE 8 0 / 20 EXAMPLE 9 0 / 20 EXAMPLE 10 0 / 20 EXAMPLE 11 0 / 20 EXAMPLE 12 0 / 20 EXAMPLE 13 0 / 20 COMPARATIVE 1 20 / 20 In the table 1, the denominators of the numerals in the column representing the number of the batteries having an occurrence of the inferior welding represent the number of all of the batteries submitted to the test of the welding and the numerators thereof represent the number of the batteries having the occurrence of the inferior welding. As shown in the table 1, in the batteries of the comparative example 1, there occur inferior welding in all of the batteries but in the batteries of the examples of the present invention, there is no occurrence of the inferior welding. Moreover, in the examples 1 to 13, all the batteries have sufficient sealing function representing 10⁻⁹atom cc/sec of helium gas in the leak examination. Although, in the examples 1 to 8, as the first sealing member 13 there is used a spherical member, it is not limited to this and there may be used such as a column sealing plug member with its top portion 13a of a spherical shape as shown in Fig. 7 or may be used a coniform member with its top portion 13a rounded as shown in Fig. 8. In other words, as the first sealing member 13, there may be used a member having a top portion with a diameter smaller than the minimum inner diameter of the electrolyte charging opening 12 and having a portion whose diameter is slightly larger than the minimum inner diameter of the electrolyte charging opening 12. Moreover, in the examples 1 to 8, although the first sealing member 13 is made of polytetrafluoroethylene material, it is not limited to this and there may be used a member which is made of ethylene-tetrafluoroethylene common polymeric material of fluorine-contained polymers, metallic material such as stainless steel or nickel. Moreover, in the examples 9 to 12, although there is used a sealing member with a head portion 13 of an oval shape as shown in Figs. 9 and 12 or with a head portion 13 of a column shape with a coniform top portion 13a as shown in Figs. 11, 13 and 14, it is not limited to these shapes and other types may be used so long as the diameter of the top portion 13a of the sealing member 13 is slightly smaller than the minimum inner diameter of the electrolyte charging opening 12 and the maximum diameter of the sealing member 13 is slightly larger than the minimum inner diameter of the electrolyte charging opening 12. Moreover, in the examples 5 to 8, although there is used a sealing member made of stainless steel, the material of the sealing member is not limited to this and other material such as nickel may be used. Moreover, in the embodiments of the present invention, although the insulating layer 8 is made of glass, it is not limited to this and the insulating layer 8 may be made of other material such as ceramics. Although, in the embodiments mentioned above, the explanation is made about a flat type sealed battery of a lithium thionyl chloride group using lithium as the negative electrode active material and thionyl chloride as the positive electrode active material and as the solvent of the electrolyte, the present invention is not limited to this, and the negative electrode active material may be made of other alkaline metal such as sodium or potassium and also the positive electrode active material may be made oxyhalogenide (oxyhalide) such as sulfuryl chloride or phosphoryl chloride which is liquid at a normal temperature (25°C), and not only the oxyhalide mentioned above but also organic electrolyte may be used as the solvent of the electrolyte. MODIFIED EXAMPLE In the flat disc type sealed battery according to the present invention, there is provided an explosion preventing mechanism mentioned later in the bottom wall 5a of the battery vessel 5. That is to say, when the flat type sealed battery is put in such an abnormal condition that the battery is exposed in a high temperature heating condition or the battery is charged with high voltage, the internal pressure of the battery is abnormally raised and the battery is ruptured under the high pressure, resulting in occurrence of so called a battery explosion with a big explosive and the contents of the battery are scattered in all directions so as to contaminate and damage the apparatus using the battery. Therefore, in order to prevent the battery explosion, there is formed an annular thinned groove 15 in the bottom wall 5a of the battery vessel 5 as shown in Fig. 15. The diameter of the annular thinned groove 15 is made to be 19 to 87 % of the outer diameter of the bottom wall 5a of the battery vessel 5, whereby the explosion of the battery can be perfectly prevented. Besides this, as shown in Fig. 16, when the annular thinned groove 15 is provided with its thickness t of 0.05 to 0.20 mm, the similar effect can be obtained. Moreover, upon combining the above two kinds of explosion preventing mechanisms according to the object of the usage of the battery, the effects of the both mechanisms are synergistically enhanced so as to obtain a more perfect explosion preventing mechanism.

Claims: A flat disc type sealed battery comprising; a battery vessel (5) having a bottom wall (5a) with an electrolyte charging opening (12) formed in the central portion thereof, a battery lid member (6) for covering the upper opening of said battery vessel, power generating components which are enclosed by sealing said battery vessel (5) and battery lid member (6), a first sealing member (13) for sealing said electrolyte charging opening (12) after the electrolyte (4) is charged into said battery vessel (5), and a second sealing member (14) for covering the lower edge portion (12a₁, 12b) of said electrolyte charging opening (12), the outer peripheral portion of said second sealing member (14) being welded to the bottom wall (5a) of the battery vessel (5), wherein said first and second sealing members are connected as one body of rivet shape and the first sealing member (13) has an outer diameter greater than the inner diameter of the electrolyte charging opening (12). The flat disc type sealed battery according to Claim 1, wherein said first sealing member (13) is spherical shaped and said second sealing member (14) is metallic plate. The flat disc type sealed battery according to Claim 1, wherein said electrolyte charging opening (12) is formed to be cylindrical shaped. The flat disc type sealed battery according to Claim 1, wherein said electrolyte charging opening (12) is formed to be taper cylindrical shaped. The flat disc type sealed battery according to claims 1 to 4 comprising an annular thinned groove (15) in the bottom wall (5a) of the battery vessel (5).

Inventors: IKENARI, SHIGERU, SATO, KIYOSHI, YOKOYAMA, KENICHI, YOSHIKAWA, HIROKAZU
Applicants: HITACHI MAXELL LTD.
Application year: 1989
Main classification: H01M2
IPC codes: H01M2