Patent Document

This application is a continuation application of U.S. patent application Ser. No. 12/711,618 filed Feb. 24, 2010, now U.S. Pat. No. 8,304,109, issued on Nov. 6, 2012, and is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-055803 filed on Oct. 3, 2009, the entire contents of which being incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a sealed battery such as a nonaqueous electrolyte secondary battery and nickel-hydrogen secondary battery and, in particular, relates to a sealed battery with high reliability which includes a current interruption mechanism inside and a connecting terminal having a structure in which an electrolyte or washing solution hardly enters the current interruption mechanism during the manufacture, and a method for manufacturing the same. 
     BACKGROUND ART 
     As power supplies for driving portable electronic equipment such as cell phones, portable personal computers, and portable music players, alkaline secondary batteries represented by a nickel hydrogen battery and nonaqueous electrolyte secondary batteries represented by a lithium ion battery are widely used. Furthermore, exhaust controls of carbon dioxide gas and the like are being tightened up in view of the recent moves to protect the environment. Thus, in the car industry, not only automobiles using fossil fuels such as gasoline, diesel oil, and natural gas, but also electric vehicles (EVs) and hybrid electric vehicles (HEVs) have been developed actively. In addition, a recent sudden rise in the price of fossil fuels has accelerated the development of EVs and HEVs. 
     The batteries for such EVs or HEVs are required to have high output characteristics, so that each battery is upsized and a number of batteries are connected in series or in parallel to be used. In particular, the sealed batteries used for such applications need to have superior safety as compared with batteries for compact equipment because, in particular, the nonaqueous electrolyte secondary batteries use materials with very high reactivity. Thus, as shown in JP-A-2008-66254 and JP-A-2008-66255, the sealed battery used for EVs or HEVs is equipped with a gas exhaust valve for releasing internal pressure when the pressure in the battery outer can increases as well as with the current interruption mechanism for interrupting the electrical connection between an external terminal and an electrode assembly in the outer can. 
     That is, as shown in  FIG. 6A , JP-A-2008-66254 discloses the invention of a sealed battery  50  which includes an external terminal  53  having a through-hole  52  through which a current interruption mechanism  51  communicates with the outer space of the sealed battery  50 . Therefore, the current interruption mechanism  51  reliably works when the pressure in an outer can  54  increases. Furthermore, as shown in  FIG. 6B , JP-A-2008-66255 discloses the invention of a sealed battery  60  which includes an external terminal  63  having a through-hole  62  through which a current interruption mechanism  61  communicates with the outer space of the sealed battery  60 . Therefore, the current interruption mechanism  61  works when the pressure in an outer can  64  increases. In addition, in the sealed battery  60 , the through-hole  62  is sealed with a resin film stopper  65  in order to prevent deterioration of the current interruption mechanism  61  from entering water or oxygen through the through-hole  62 . 
     Each through-hole of the sealed batteries disclosed in JP-A-2008-66254 and JP-A-2008-66255 is installed in order that the space on the current interruption mechanism at the side corresponding to the outside of the battery communicates with the outside of the battery, so that the current interruption mechanism works easier when the pressure in the outer can increases. Thus, the resin film stopper  65  used in the sealed battery  60  disclosed in JP-A-2008-66255 needs to be thin and is not considered to be a strong stopper. Because of this, in the sealed battery  60  disclosed in JP-A-2008-66255, the film stopper  65  may be broken by any impact from the outside, and moreover, when the film stopper  65  is broken, entering water, oxygen, or the like from the outside may deteriorate the current interruption mechanism  61  as shown in JP-A-2008-66254. 
     However, experiments by the inventors reveal that the action of the current interruption mechanism makes substantially no difference whether the space on the current interruption mechanism at the side corresponding to the outside of the battery is closed or open. That is, even when the pressure in the outer can is increased for some reason, because the pressure of gas generated in the battery under abnormal conditions is very high, the pressure in the closed space on the current interruption mechanism at the side corresponding to the outside of the battery seldom simultaneously increases equally. Thus, there is no problem even when the space on the current interruption mechanism at the side corresponding to the outside of the battery is sealed. 
     SUMMARY 
     The present invention is based on the above described experimental results. An advantage of some aspects of the invention is to provide a sealed battery with high reliability including a connecting terminal having a structure in which an electrolyte or washing solution hardly enters a current interruption mechanism during the manufacture and a method for manufacturing the same. 
     According to a first aspect of the invention, a sealed battery includes: an outer can having a mouth; in the outer can, an electrode assembly having a positive electrode plate and a negative electrode plate equipped with a positive electrode collector plate and a negative electrode collector plate, respectively; a sealing plate sealing the mouth of the outer can; and an external terminal attached to the sealing plate and having a connecting terminal. In the sealed battery, the connecting terminal and the electrode assembly are electrically connected; in a conductive pathway electrically connecting the connecting terminal and the electrode assembly, a current interruption mechanism to interrupt current in response to pressure increase in the outer can, is installed; the connecting terminal includes inside a through-hole continuing to a space on the current interruption mechanism at a side corresponding to the outside of the battery; and the through-hole is sealed with a terminal stopper made of an elastic member to form a closed space between the terminal stopper and the current interruption mechanism. 
     The through-hole formed in the connecting terminal is for examining leakage of the current interruption mechanism in the assembly process, but during pouring an electrolyte or washing, the electrolyte or washing water may enter the through-hole of the connecting terminal. When the electrolyte or washing water enters the through-hole, the current interruption mechanism may corrode, which may cause a malfunction. In the sealed battery according to the aspect of the invention, the through-hole is sealed with the terminal stopper made of an elastic member, and moreover, the space enclosed with the through-hole and current interruption mechanism is made a closed space, so that the electrolyte or washing water does not enter the through-hole. Thus, the malfunction due to the corrosion of the current interruption mechanism does not occur, and consequently, a sealed battery with high reliability can be obtained. 
     Furthermore, in the sealed battery according to the aspect of the invention, the through-hole of the connecting terminal is tightly sealed with the terminal stopper made of an elastic member. However, the closed space is formed between the current interruption mechanism and the terminal stopper, and moreover, the pressure of gas generated in the battery under abnormal conditions becomes very high, so that the action of the current interruption mechanism is not adversely affected. The sealed battery according to the aspect of the invention is applicable to any of the following batteries: a battery in which the electrode assembly is for a nonaqueous electrolyte secondary battery; a battery in which the electrode assembly is for an aqueous electrolyte secondary battery such as a nickel-hydrogen secondary battery using an aqueous electrolyte; a battery in which the electrode assembly is a rolled electrode assembly which is formed by rolling a positive electrode plate and negative electrode plate with a separator interposed therebetween; and a battery in which the electrode assembly is a laminated electrode assembly which is formed by laminating a positive electrode plate and negative electrode plate with a separator interposed therebetween. 
     Furthermore, in the sealed battery according to the aspect of the invention, it is preferable that the terminal stopper includes the elastic member and a metal plate, and the metal plate is welded to the connecting terminal. 
     The terminal stopper may fall off by vibration and the like because of being composed of an elastic member. In the sealed battery according to the aspect of the invention, the terminal stopper composed of the elastic member and metal plate is used, and moreover, the metal plate is welded to the connecting terminal by laser welding or the like, so that the through-hole can be sealed more tightly. Here, the diameter of the metal plate is preferably substantially the same as or slightly larger than the head diameter of the terminal stopper. 
     Furthermore, in the sealed battery according to the aspect of the invention, it is preferable that: the through-hole formed in the connecting terminal includes a large diameter portion formed outside of the outer can and a small diameter portion formed inside of the outer can; the terminal stopper includes, at an upper end, a head portion having a diameter larger than that of the small diameter portion of the through-hole and smaller than that of the large diameter portion of the through-hole, at a lower end, a protruding portion having a diameter smaller than that of the head portion and larger than that of the small diameter portion of the through-hole, a locking portion tapering from the protruding portion, and between the head portion and the protruding portion, a connecting portion having almost the same diameter as that of the small diameter portion of the through-hole and having substantially the same length as that of the small diameter portion of the through-hole; and the terminal stopper is attached to the through-hole in which the head portion is placed on a side of the large diameter portion of the through-hole and the locking portion is protruded from an end of the small diameter portion of the through-hole. 
     The through-hole formed in the connecting terminal in the sealed battery according to the aspect of the invention includes the large diameter portion formed outside of the outer can and the small diameter portion formed inside of the outer can, and the cross section is T-shaped. Furthermore, the terminal stopper used in the sealed battery according to the aspect of the invention includes, at the upper end, the head portion having a diameter larger than that of the small diameter portion of the through-hole formed in the connecting terminal and smaller than that of the large diameter portion of the through-hole, at the lower end, the protruding portion having a diameter smaller than that of the head portion and larger than that of the small diameter portion of the through-hole, the locking portion tapering from the protruding portion, and between the head portion and the protruding portion, the connecting portion having almost the same diameter as that of the small diameter portion of the through-hole and having substantially the same length as that of the small diameter portion of the through-hole. Thus, when the terminal stopper is inserted from the locking portion side into the through-hole formed in the connecting terminal, because the terminal stopper is composed of an elastic member, the protruding portion is deformed to pass through the small diameter portion of the through-hole, and protruded from the small diameter portion of the through-hole to recover the original shape. At the same time, the head portion of the terminal stopper is caught by the small diameter portion of the through-hole to fit into the large diameter portion of the through-hole. Therefore, in the sealed battery according to the aspect of the invention, the terminal stopper is tightly fixed to the connecting terminal, and thus an electrolyte or washing water still does not enter the through-hole. 
     Furthermore, in the sealed battery according to the aspect of the invention, it is preferable that the current interruption mechanism is deformed in response to pressure increase in the outer can to interrupt electrical connection between the connecting terminal and the electrode assembly. 
     In the sealed battery according to the aspect of the invention, when the current interruption mechanism is deformed in response to the pressure increase in the outer can, the deformation is not inhibited, because a space is formed between the current interruption mechanism and terminal stopper. Thus, with the sealed battery according to the aspect of the invention, when the pressure in the outer can increases, the current interruption mechanism can be reliably deformed to reliably interrupt the electrical connection between the connecting terminal and electrode assembly. Here, the current interruption mechanism may include a metal plate for sealing so as to form a predetermined space in the through-hole of the connecting terminal, and a collector welded to the metal plate and having a cyclic thin-wall groove around the periphery of the welded part, or metal foil that is welded to the metal plate and to a collector around the periphery of the welded part. Therefore, the current interruption mechanism can employ the structure in which the collector is broken along the cyclic thin-wall groove or the metal foil is broken when the pressure in the outer can increases to deform the metal plate. In this case, the space enclosed with the through-hole of the connecting terminal and the current interruption mechanism is not required to communicate with the outside and may be a closed space. 
     According to another aspect of the invention, a method for manufacturing a sealed battery having an outer can with a mouth, an electrode assembly with a positive electrode plate and a negative electrode plate, a positive electrode collector plate and a negative electrode collector plate attached to the positive electrode plate and the negative electrode plate, respectively, and a sealing plate with an external terminal having a connecting terminal with a through-hole and an electrolyte pouring hole, the method includes a first step of attaching a current interruption mechanism to the connecting terminal to seal one end of the through-hole; a second step of flowing a gas from the other end of the through-hole to examine air leakage between the connecting terminal and the current interruption mechanism; and a third step of inserting a terminal stopper made of an elastic member into the through-hole. 
     In the method for manufacturing a sealed battery according to the aspect of the invention, because the air leakage between the connecting terminal and current interruption mechanism is examined in the second step, batteries with welding defects can be screened out in the assembly process, and moreover, because the terminal stopper made of an elastic member is inserted into the through-hole in the third step, entering an electrolyte into the through-hole can be inhibited during subsequent electrolyte pouring and water washing performed as necessary. Thus, according to the method for manufacturing a sealed battery according to the aspect of the invention, defectives are screened out in the process and a malfunction due to the corrosion of the current interruption mechanism does not occur, and consequently, a sealed battery with high reliability can be manufactured. Here, examples of the gas used for examining air leakage include an inert gas such as nitrogen (N 2 ) gas and dry air. 
     Furthermore, in the method for manufacturing a sealed battery according to the aspect of the invention, it is preferable that, in the third step, the terminal stopper composed of the elastic member and a metal plate is used, the terminal stopper made of the elastic member is inserted into the through-hole, and thereafter the metal plate is welded to the connecting terminal. 
     The terminal stopper may fall off by vibration and the like because of being composed of an elastic member. In the method for manufacturing a sealed battery according to the aspect of the invention, the terminal stopper composed of the elastic member and metal plate is used, and moreover, the metal plate is welded to the connecting terminal, so that the through-hole can be sealed more tightly. When the metal plate is welded, the welding is easier to perform by the laser welding method. 
     Furthermore, in the method for manufacturing a sealed battery according to the aspect of the invention, the current interruption mechanism includes the sealing tab, the inversion plate, and a collector having a breaking portion, wherein the method preferably includes attaching an inversion plate to a sealing tab, and thereafter, flowing a gas from the other end of the through-hole to examine. 
     According to the method for manufacturing a sealed battery according to the aspect of the invention, because the current interruption mechanism including the sealing tab, inversion plate, and collector having the breaking portion is used, the inversion plate is attached to the sealing tab, and thereafter, the air leakage between the sealing tab and inversion plate is examined. Therefore, the battery with welding defects can be screened out more exactly in the assembly process, and consequently, a sealed battery with higher reliability can be manufactured. 
     Furthermore, in the method for manufacturing a sealed battery according to the aspect of the invention, the method preferably includes attaching the breaking portion of the collector to the inversion plate, and thereafter, flowing a gas from the other end of the through-hole to examine. 
     According to the method for manufacturing a sealed battery according to the aspect of the invention, because the breaking portion of the collector is attached to the inversion plate, and thereafter, the air leakage between the inversion plate and the breaking portion of the collector is examined again, the battery with welding defects can be screened out more exactly in the assembly process. As a result of this, a sealed battery with higher reliability can be manufactured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a sealed battery in the embodiment of the invention. 
         FIG. 2  is an exploded perspective view of an external terminal of the sealed battery shown in  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the external terminal of the sealed battery shown in  FIG. 1 . 
         FIG. 4  is a cross-sectional view of a terminal stopper in the embodiment of the invention. 
         FIGS. 5A through 5F  are cross-sectional views showing a successive assembling process of the external terminal of the sealed battery in the embodiment of the invention. 
         FIG. 6A  is a cross-sectional view of an external terminal of a sealed battery of a related art example, and  FIG. 6B  is a cross-sectional view of an external terminal of a sealed battery of another related art example. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, exemplary embodiments of the invention will be described in detail with drawings, and, in the description below, the positive electrode external terminal of the positive electrode plate will be exemplified. In a sealed battery  10  of the present embodiment, as shown in  FIG. 1  and  FIG. 2 , a positive electrode plate and negative electrode plate are rolled and pressed into a flat shape to form a rolled electrode assembly  12 , the rolled electrode assembly  12  is stored in an outer can  11  in a transversal direction with respect to the axis direction of the outer can  11 , and a mouth of the outer can  11  is sealed with a sealing plate  13 . Furthermore, to the sealing plate  13 , a gas exhaust valve  14 , electrolyte pouring hole (not shown in the drawings) and sealing member  15  for the electrolyte pouring hole are installed. The gas exhaust valve  14  opens when the gas pressure is higher than the working pressure of a current interruption mechanism. 
     In addition, to the sealing plate  13 , a positive electrode external terminal  16  and negative electrode external terminal  17  are formed outside of the sealed battery  10 . The positive electrode external terminal  16  and negative electrode external terminal  17  are used with a suitable shaped terminal block, external connecting terminal, or the like (not shown in the drawings) according to whether the sealed battery is used alone, or the sealed batteries connected in series or in parallel are used, and the like. Hereinafter, the structure of the positive electrode external terminal  16  for the positive electrode plate will be described. 
     As shown in  FIG. 2  and  FIG. 3 , a current collecting tab  21  is connected to, for example, a plurality of positive electrode substrates  20  protruded from one end of the rolled electrode assembly  12 . From the current collecting tab  21 , a collector  22  is extended. A connecting terminal  23  has a cylinder portion  23   a , and a through-hole  23   b  is formed inside of the connecting terminal  23 . Then, the cylinder portion  23   a  of the connecting terminal  23  is inserted into each hole formed in a gasket  24 , the sealing plate  13 , an insulating plate  25 , and a sealing tab  26 , and a leading end portion  23   c  is crimped to be fixed integrally. 
     Furthermore, a periphery of an inversion plate  27  is welded to a leading end portion of the sealing tab  26 , and the collector  22  is welded to a central part of the inversion plate  27  by laser welding. A collector holder  28  made of resin is placed on peripheral parts of the collector  22  and inversion plate  27  for positioning of the collector  22  and inversion plate  27  and for electrical insulation of the peripheral parts. Therefore, the positive electrode substrate  20  is electrically connected to the connecting terminal  23  through the current collecting tab  21 , collector  22 , inversion plate  27 , and sealing tab  26 . In addition, such connecting terminal  23 , gasket  24 , sealing plate  13 , insulating plate  25 , sealing tab  26 , inversion plate  27 , collector holder  28 , and collector  22  form the positive electrode external terminal  16  of the embodiment. 
     Here, the inversion plate  27  and collector  22  form a current interruption mechanism  18  according to an embodiment of the invention. That is, on the collector  22 , a cyclic groove  22   a  is formed around the laser welded portion, and whereby, a portion with thin thickness is circularly formed. The inversion plate  27  is made to swell toward the through-hole  23   b  of the connecting terminal  23  when the pressure in the outer can  11  increases, and the collector  22  is welded to the central part of the inversion plate  27 . Therefore, the collector  22  is broken at the cyclic groove  22   a  when the pressure in the outer can  11  exceeds a predetermined value, and accordingly, the electrical connection between the inversion plate  27  and collector  22  is interrupted. The current interruption mechanism  18  may employ another structure in which metal foil is welded to the inversion plate  27 , then, the periphery of the welded part is welded to the collector to be used, and the metal foil is broken when the pressure in the outer can  11  increases to deform the inversion plate  27 . 
     Furthermore, the through-hole  23   b  formed in the connecting terminal  23  has a large diameter portion  23   d  outside of the outer can  11  and a small diameter portion  23   e  inside of the outer can  11 . As shown in  FIG. 3 , the through-hole  23   b  of the connecting terminal  23  is tightly sealed with a rubber terminal stopper  30 . As shown in  FIG. 4 , the terminal stopper  30  includes, at the upper end, a head portion  31  having a diameter larger than that of the small diameter portion  23   e  of the through-hole  23   b  of the connecting terminal  23  and smaller than that of the large diameter portion  23   d , at the lower end, a protruding portion  32  having a diameter smaller than that of the head portion  31  and larger than that of the small diameter portion  23   e  of the through-hole  23   b , a locking portion  33  tapering from the protruding portion  32 , and between the head portion and the protruding portion, a connecting portion  34  having almost the same diameter as that of the small diameter portion  23   e  of the through-hole  23   b  of the connecting terminal  23  and having substantially the same length as that of the small diameter portion  23   e . Then, the terminal stopper  30  is attached to the through-hole  23   b  so that the head portion  31  would be placed on a side of the large diameter portion  23   d  of the through-hole  23   b  of the connecting terminal  23  and the locking portion  33  would be protruded from the end of the small diameter portion  23   e  of the through-hole  23   b  of the connecting terminal  23 . Here, in order to strengthen the head portion  31  even when the thickness is made thin, a metal plate  35  made of aluminum or the like is installed on the surface of the head portion  31  of the terminal stopper  30 . 
     The metal plate  35  can be welded to the connecting terminal  23  by, for example, laser welding. The terminal stopper  30  may fall off by vibration and the like because of being composed of an elastic member. However, when the metal plate  35  is welded to the connecting terminal  23 , the through-hole  23   b  can be sealed more tightly with the terminal stopper  30 . 
     The successive assembling process of the positive electrode external terminal  16  will be described with  FIG. 5 . First, the gasket  24  and connecting terminal  23  are arranged on the sealing plate  13 , the cylinder portion  23   a  of the connecting terminal  23  is inserted into each mouth formed in the gasket  24  and sealing plate  13 . Then, the cylinder portion  23   a  of the connecting terminal  23  is inserted into each mouth formed in the insulating plate  25  and sealing tab  26  from the opposite side of the gasket  24 . After that, the leading end portion  23   c  of the cylinder portion  23   a  of the connecting terminal  23  is crimped to be fixed with the connecting terminal  23 , gasket  24 , sealing plate  13 , insulating plate  25 , and sealing tab  26 , integrally ( FIG. 5A ). 
     Then, the periphery of the sealing tab  26  is welded to the inversion plate  27  so as to totally seal the periphery of the inversion plate  27  ( FIG. 5B ). Here, for the inversion plate  27 , a thin aluminum plate is shaped so as to protrude downward to be used. The welding method between the sealing tab  26  and inversion plate  27  may employ laser welding method or ultrasonic welding method. Then, a gas, for example, an inert gas such as N 2  gas or dry air, with a predetermined pressure is introduced from the top of the connecting terminal  23  into the through-hole  23   b  to examine the sealing of the welded part between the sealing tab  26  and inversion plate  27  ( FIG. 5C ). The product that is determined to have incomplete sealing by the examination is excluded. 
     With regard to the product that is determined to have the passed welded part between the sealing tab  26  and inversion plate  27 , the collector holder  28  made of resin is brought into contact with the inversion plate  27 , the collector holder  28  and insulating plate  25  are latched, and then, a region surrounded by the groove  22   a  of the collector  22  and the inversion plate  27  are welded by the laser welding method or ultrasonic welding method ( FIG. 5D ). Thus, the current interruption mechanism  18  of the embodiment is completed. 
     Because the welding may adversely affect the welded part between the sealing tab  26  and inversion plate  27 , a gas with a predetermined pressure is once again introduced from the top of the connecting terminal  23  into the through-hole  23   b  to examine the sealing of the welded part between the sealing tab  26  and inversion plate  27  ( FIG. 5E ). The second examination provides the higher reliability of the positive electrode external terminal  16  of the embodiment. However, the second examination is not always a necessary step, and may be carried out as necessary. 
     Then, the terminal stopper  30  is inserted into the through-hole  23   b  of the connecting terminal  23  ( FIG. 5F ), as necessary, the metal plate  35  of the terminal stopper  30  is welded to the connecting terminal  23  by, for example, laser welding to complete the positive electrode external terminal  16  for the positive electrode plate of the embodiment. The positive electrode external terminal  16  for the positive electrode plate may be used without any modification, but may be used with a suitable shaped terminal block, external connecting terminal, or the like (not shown in the drawings) attached according to whether the sealed battery  10  is used alone, or the sealed batteries  10  connected in series or in parallel are used, and the like. 
     Here, the structure of the positive electrode external terminal  16  for the positive electrode plate is described, but the structure may be employed to the negative electrode external terminal  17  for the negative electrode plate. However, when the structure having the current interruption mechanism  18  as described above is employed as the positive electrode external terminal  16  for the positive electrode plate, the negative electrode external terminal  17  for the negative electrode plate is not required to employ the current interruption mechanism. Therefore, the negative electrode external terminal  17  for the negative electrode plate can employ a simpler structure. 
     In order to complete the sealed battery  10  of the embodiment, the rolled electrode assembly  12  attached to the positive electrode external terminal  16  is inserted into the outer can  11 , the sealing plate  13  is fitted to the mouth of the outer can  11 , the fitted portion is sealed by laser welding, next, a predetermined amount of electrolyte is poured from the electrolyte pouring hole (not shown in the drawings), and then the electrolyte pouring hole is sealed with a sealing member  15 . When pouring the electrolyte at this time, because the electrolyte may adhere to the surfaces of the outer can  11 , sealing plate  13 , and the like, the surfaces need to be cleaned by water washing. However, in the sealed battery  10  of the embodiment, because the terminal stopper  30  is tightly inserted into the through-hole  23   b  of the connecting terminal  23 , the electrolyte or washing water cannot enter the through-hole  23   b  of the connecting terminal  23 , whereby, the action of the current interruption mechanism  18  is not adversely affected. 
     In addition, in the sealed battery  10  of the embodiment, the space on the current interruption mechanism  18  at the side corresponding to the outside of the battery is totally sealed. However, even when the pressure in the outer can  11  is increased by any reason, because the pressure of gas generated in the battery under abnormal conditions is very high, the pressure in the closed space on the current interruption mechanism  18  at the side corresponding to the outside of the battery seldom simultaneously increases equally. Thus, there is no problem even when the space on the current interruption mechanism  18  at the side corresponding to the outside of the battery is sealed.

Technology Category: 5