Patent Publication Number: US-2015072179-A1

Title: Sealed battery

Description:
TECHNICAL FIELD 
     The present invention relates to a sealed-type secondary battery having a current interrupt device for interrupting a current in emergency. 
     BACKGROUND ART 
     Conventionally, a sealed-type secondary battery (hereinafter referred to as the “sealed battery”) is widely known, the sealed battery including an electrode body made by laminating and winding a pair of sheet-like electrodes (positive and negative electrodes) and separators interposed therebetween, and a case in which the electrode body and an electrolyte are stored. 
     In the sealed battery as mentioned above, in case of being in an overcharge condition, a gas resulting from a decomposition reaction of the electrolyte in the case causes an increase of the pressure in the case. This may cause a problem that the case is damaged for example. 
     In order to solve the above-mentioned problem, proposed is a sealed battery having a current interrupt device (hereinafter referred to as the “CID”) which interrupts a current if the pressure in the case is a predetermined value or more (for example, see Patent Literature 1). 
     The CID, for example, includes an inversion plate which is connected to an external terminal and which is transformed in association with an increase of the pressure in the case, and a collecting plate which is connected to the inversion plate and one electrode of the electrode body. In the CID, the collecting plate connected to the inversion plate is transformed in association with transformation of the inversion plate, and the collecting plate is ruptured if the collecting plate is subjected to stress of a predetermined value or more, thereby a current in the sealed battery being interrupted. 
     Recently, as a lifetime of the sealed battery is prolonged, there is growing concern about time degradation of the CID. 
     The time degradation of the CID is caused by variation of the pressure in the case associated with the use of the sealed battery. The pressure in the case increases and decreases repeatedly due to variation of temperature and the like. Thereby, the collecting plate is fatigued, and may be ruptured even if the pressure in the case does not reach a value required to rupture the collecting plate. In other words, a pressure (the pressure in the case) required to run the CID becomes lower. 
     Since the CID acts as a safeguard, long-term operation guarantee is required for the CID. 
     Therefore, in the sealed battery having the CID, it is greatly expected that the time degradation of the CID is suppressed. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: WO 2010/053100 A1 
       
    
     SUMMARY OF INVENTION 
     Problem to be Solved by the Invention 
     The objective of the present invention is to provide a sealed battery capable of suppressing time degradation of a CID. 
     Means for Solving the Problem 
     A first aspect of the invention is a sealed battery including an electrode body which is impregnated with an electrolyte to function as a power generation element, a case in which the electrode body and the electrolyte are stored, and a current interrupt device which interrupts a current in emergency. The current interrupt device includes an inversion plate which is transformed in association with an increase of a pressure in the case, and a collecting plate having a pair of plate surfaces, which is connected to the inversion plate and which is transformed in association with a transformation of the inversion plate. The collecting plate has a carved part formed in a groove, which is ruptured if the pressure in the case is a predetermined value or more, and a plurality of slits which is formed to penetrate through the pair of plate surfaces. The plurality of slits is arranged in the vicinity of the carved part, and is formed to open when the collecting plate is transformed. 
     Preferably, the plurality of slits is formed to intersect with the carved part. 
     Preferably, each of the plurality of slits is linearly formed, and is arranged to be perpendicular to the carved part. 
     Preferably, the carved part is formed in a perfect circle, and the plurality of slits is radially arranged at equal intervals. 
     Preferably, the collecting plate has a thin part which is formed around a part, connected to the inversion plate, of the collecting plate, and which has a thickness smaller than that of the other part of the collecting plate, the carved part and the plurality of slits are arranged in the thin part, and the thin part is curved in a wavy shape from the middle to the outer edge thereof. 
     Effects of the Invention 
     The present invention makes it possible to suppress time degradation of a CID. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a sealed battery according to an embodiment of the present invention. 
         FIG. 2  shows a thin part of a collecting plate, in which  FIG. 2(   a ) is a sectional side end view thereof, and  FIG. 2(   b ) is a bottom view thereof. 
         FIG. 3  shows how the thin part of the collecting plate is transformed. 
         FIG. 4  shows how slits formed in the thin part of the collecting plate open. 
         FIG. 5  is a schematic view showing how a conventional thin part is transformed. 
         FIG. 6  is a schematic view showing how the thin part according to the embodiment of the present invention is transformed, in which  FIG. 6(   a ) is a side view, and  FIG. 6(   b ) is a plan view. 
         FIG. 7  shows results obtained by analyzing stress generated on a carved part of the thin part by means of CAE. 
         FIG. 8  shows a thin part of a collecting plate according to another embodiment of the present invention. 
         FIG. 9  shows a thin part of a collecting plate according to another embodiment of the present invention. 
         FIG. 10  shows a thin part of a collecting plate according to another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     With reference to  FIGS. 1 to 4 , described below is a battery  1  as an embodiment of a sealed battery according to the present invention. 
     The battery  1  is what is called a cylindrical battery. 
     For convenience, a top-bottom direction in  FIG. 1  is defined as a top-bottom direction of the battery  1 . 
     Moreover, in the following description, an upper side and a lower side generally mean the outer side and the inner side of the battery  1 , respectively. 
     As shown in  FIG. 1 , the battery  1  is a sealed-type secondary battery, and includes an electrode body  10  which is impregnated with an electrolyte to function as a power generation element, a case  20  in which the electrode body  10  and the electrolyte are stored, and a CID  100  which interrupts a current in emergency. 
     The electrode body  10  is made by laminating and cylindrically winding a pair of sheet-like electrodes (positive and negative electrodes) and separators interposed therebetween. The electrode body  10  acts as a power generation element when being impregnated with the electrolyte. 
     The case  20  is a substantially cylindrical member forming an exterior of the battery  1 . 
     The case  20  includes a storage part  21 , and a lid part  22 . 
     The storage part  21  is a bottomed cylindrical member whose top end is open, and is made of an electrically conductive material such as aluminum or iron. Inside the storage part  21 , the electrode body  10  and the electrolyte are stored. The bottom part (lower end part) of the storage part  21  is electrically connected to the negative electrode of the electrode body  10  through a negative-electrode collecting member with electrical conductivity (not shown). The storage part  21  acts as a negative electrode terminal of the battery  1 . 
     The lid part  22  is a substantially disk-like member for closing the opening of the storage part  21 , and is made of an electrically conductive material such as aluminum or iron. The lid part  22  is arranged to cover the opening of the storage part  21 . The upper end part of the storage part  21  and the outer circumferential part of the lid part  22  are fixed to each other through an insulative gasket  23 . The central part of the lid part  22  upward protrudes. The lid part  22  is electrically connected to the positive electrode of the electrode body  10  through a positive-electrode lead  24  with electrical conductivity, and members (specifically, an after-mentioned inversion plate  110  and an after-mentioned collecting plate  120 ) constituting the CID  100 . The lid part  22  acts as a positive electrode terminal of the battery  1 . 
     The lid part  22  has a plurality of vents  22   a  penetrating through both the plate surfaces thereof. 
     Therefore, the space in the storage part  21  is not sealed by the lid part  22 . In other words, the plurality of vents  22   a  provides communication between the inside and the outside of the case  20 . 
     The CID  100  is a current interrupt device which interrupts a current if the battery  1  is in an overcharge condition and a pressure in the case  20  of abnormally increases. 
     The CID  100  includes the inversion plate  110  and the collecting plate  120 . 
     The inversion plate  110  and the collecting plate  120  are substantially disk-like members with electrical conductivity. An insulator  130  is interposed between the inversion plate  110  and the collecting plate  120 . 
     The insulator  130  is an annular member with electrical insulation property. The insulator  130  is configured to come in contact with the outer circumferential part of the inversion plate  110  and the outer circumferential part of the collecting plate  120 . Thus, the insulator  130  interrupts electrical conduction between the outer circumferential part of the inversion plate  110  and the outer circumferential part of the collecting plate  120 . 
     The inversion plate  110  and the collecting plate  120  are, similarly to the lid part  22  of the case  20 , fixed to the storage part  21  of the case  20  through the gasket  23 . 
     Specifically, the lid part  22 , the inversion plate  110 , the insulator  130  and the collecting plate  120  are concentrically laminated from above in the order mentioned, and are fixed in the upper end part of the storage part  21  with the outer circumferential parts of these members grasped by the gasket  23 . Thus, the outer circumferential parts of the lid part  22  and the inversion plate  110  are electrically connected to each other, and the gasket  23  interrupts electrical conduction between the storage part  21 , and the lid part  22 , the inversion plate  110  and the collecting plate  120 . 
     The inversion plate  110  is a member for forming an enclosed space inside the case  20 . The inversion plate  110  is formed to gradually come into proximity with the collecting plate  120  (to gradually dent downward) toward the central part thereof. 
     As mentioned previously, since the lid part  22  has the plurality of vents  22   a , the lid part  22  cannot form the enclosed space inside the case  20 . However, since the inversion plate  110  is arranged below the lid part  22  so as to close the opening of the storage part  21 , the inversion plate  110  forms the enclosed space inside the case  20 . 
     A carved part  111  in the shape of a groove is formed on the upper surface of the inversion plate  110 . 
     The carved part  111  is formed in such a manner that the upper surface of the inversion plate  110  is downward carved, and is continuously formed in a circumferential direction of the inversion plate  110 . In other words, the carved part  111  is formed in a continuous circle on the upper surface of the inversion plate  110 , and is arranged concentrically with the inversion plate  110 . 
     The collecting plate  120  is electrically connected to the positive electrode of the electrode body  10  through the positive-electrode lead  24 . 
     Specifically, one end of the positive-electrode lead  24  is connected to the lower surface of the collecting plate  120 , and the other end of the positive-electrode lead  24  is connected to the positive electrode of the electrode body  10 . 
     A thin part  121  whose thickness (distance between the surface of the collecting plate  120  facing to the electrode body  10  and the opposite surface thereof) is smaller than that of the other part of the collecting plate  120  is formed in the central part of the collecting plate  120 . 
     The thin part  121  is formed around the part of the collecting plate  120  connected to the inversion plate  110 . Specifically, the thin part  121  is formed from the part of the collecting plate  120  connected to the inversion plate  110  toward the middle part of the collecting plate  120  in a radial direction thereof. The thin part  121  is formed in substantially a disk, and is arranged concentrically with the collecting plate  120 . 
     Details for structure of the thin part  121  are described later. 
     A fitting hole  122  penetrating through both the plate surfaces of the thin part  121  in the top-bottom direction is formed in the central part of the thin part  121 . 
     The fitting hole  122  is a through hole in which the central part of the inversion plate  110  is fit. 
     The part of the inversion plate  110  in contact with the thin part  121  of the collecting plate  120 , and the part of the thin part  121  in contact with the inversion plate  110  are joined by means of welding or the like with the central part of the inversion plate  110  fit in the fitting hole  122 . Thereby, the inversion plate  110  and the collecting plate  120  are electrically connected to each other, and consequently the lid part  22  and the positive electrode of the electrode body  10  are electrically connected to each other. 
     Thus, the collecting plate  120  is connected to the inversion plate  110  in the vicinity of the center of the collecting plate  120 . Moreover, as mentioned previously, the outer circumferential part of the collecting plate  120  is separated from the outer circumferential part of the inversion plate  110  by the insulator  130 . 
     Therefore, a predetermined space is formed between the inversion plate  110  and the collecting plate  120 . 
     A plurality of communicating holes  120   a  is formed in the part of the collecting plate  120  situated radially outward of the thin part  121 . 
     The plurality of communicating holes  120   a  is formed to penetrate through both the plate surfaces of the collecting plate  120  in the top-bottom direction. 
     Therefore, if a gas results from a decomposition reaction of the electrolyte in the space below the collecting plate  120 , the gas enters the space between the inversion plate  110  and the collecting plate  120  through the plurality of communicating holes  120   a.    
     As shown in  FIGS. 2(   a ) and  2 ( b ), the thin part  121  is formed in a perfect circle, and is formed from the fitting hole  122  toward the middle part of the collecting plate  120  in the radial direction. A carved part  123  in the shape of a groove is formed on the surface of the thin part  121  facing to the electrode body  10 . 
     The carved part  123  is substantially similar in configuration to the carved part  111  of the inversion plate  110 , and is formed in such a manner that the surface of the thin part  121  facing to the electrode body  10  is carved. The carved part  123  is continuously formed in the circumferential direction of the thin part  121 , and is arranged concentrically with the thin part  121 . In other words, the carved part  123  is formed in a perfect circle. 
     In  FIG. 2(   b ), for convenience, the parts of the collecting plate  120  other than the thin part  121  are omitted. 
     As shown in  FIG. 2(   a ), the thin part  121  is curved in a wavy shape from the central part to the outer circumferential part thereof. 
     Specifically, the thin part  121  is curved in the top-bottom direction from the central part to the outer circumferential part thereof, and is formed so that all the shapes of the cutting surfaces thereof along the radial direction are substantially same. In other words, the thin part  121  has a shape in which an annular plate is bent along the radial direction. The thin part  121  having such a shape may be formed by means of press working or the like. 
     As shown in  FIG. 2(   b ), the thin part  121  has a plurality of slits  124  (twelve slits  124  in the present embodiment). 
     The plurality of slits  124  is radially arranged at equal intervals around the fitting hole  122 . 
     The slit  124  penetrates through both the plate surfaces of the thin part  121 , and is linearly formed from the vicinity of the fitting hole  122  of the thin part  121  to the vicinity of the outer circumferential part of the thin part  121 . The slit  124  is formed to intersect with the carved part  123 , and to be perpendicular to the carved part  123 . In other words, the slit  124  is formed in the radial direction of the thin part  121  so as to perpendicularly intersect with the carved part  123 . 
     As shown in  FIG. 3 , if the pressure in the case  20  (specifically, the pressure in the space between the storage part  21  and the inversion plate  110 ) is increased by the gas resulting from a decomposition reaction of the electrolyte, the gas enters the space between the inversion plate  110  and the collecting plate  120  through the plurality of communicating holes  120   a  of the collecting plate  120 , and thereby the inversion plate  110  is upward pressed and transformed. Consequently, the part, connected to the inversion plate  110 , of the thin part  121  of the collecting plate  120  is upward pulled, and the thin part  121  is transformed. 
     At this time, as shown in  FIG. 4 , the plurality of slits  124  formed in the thin part  121  opens in association with transformation of the thin part  121 . 
     This makes it possible to suppress interfering with circumferential transformation of the thin part  121 , and to reduce stress generated on the carved part  123  of the thin part  121 . 
     Therefore, it is possible to minimize fatigue of the carved part  123  which is to be accumulated in the case where the pressure in the case  20  increases and decreases at a relatively low level due to variation of temperature of the battery  1  in use, and the like. Consequently, it is possible to suppress time degradation of the CID  100 . 
     Moreover, as shown in  FIG. 3 , if the pressure in the case  20  increases, and the part, connected to the inversion plate  110 , of the thin part  121  of the collecting plate  120  is upward pulled, the wavy part of the thin part  121  is stretched. In other words, since the thin part  121  is curved in a wavy shape (see  FIG. 2(   a )), the curved part thereof is stretched and transformed if the part, connected to the inversion plate  110 , of the thin part  121  of the collecting plate  120  is upward pulled in association with an increase of the pressure in the case  20 . 
     This makes it possible to reduce stress which is generated on the thin part  121  if the part, connected to the inversion plate  110 , of the thin part  121  of the collecting plate  120  is upward pulled in association with the increase of the pressure in the case  20 . Specifically, even if the part, connected to the inversion plate  110 , of the thin part  121  of the collecting plate  120  is upward pulled in association with the increase of the pressure in the case  20 , the thin part  121  is not subjected to relatively large stress as long as the wavy part of the thin part  121  is not completely stretched. Thus, the stress generated on the thin part  121  can be reduced. 
     Therefore, it is possible to minimize fatigue of the carved part  123  which is accumulated in the case where the pressure in the case  20  increases and decreases at a relatively low level due to variation of temperature of the battery  1  in use, and the like. Consequently, it is possible to suppress time degradation of the CID  100 . 
     If the pressure in the case  20  further increases, and the carved part  123  of the thin part  121  is subjected to stress of a predetermined value or more, the carved part  123  is ruptured. Thereby, electrical conduction between the inversion plate  110  and the collecting plate  120  is interrupted, and consequently a current in the battery  1  is interrupted. 
     If the pressure in the case  20  much further increases, the inversion plate  110  is further upward pulled, and the carved part  111  of the inversion plate  110  is ruptured. Thereby, communication between the spaces above and below the inversion plate  110  in the case  20  is provided, and the gas resulting from a decomposition reaction of the electrolyte is discharged to the outside of the case  20  through the plurality of vents  22   a  of the lid part  22 . 
     This makes it possible to prevent the case  20  from breaking if the gas resulting from a decomposition reaction of the electrolyte increases the pressure in the case  20 . 
     With reference to  FIGS. 5 and 6 , described below is how the thin part  121  of the collecting plate  120  is transformed if the pressure in the case  20  increases. 
       FIG. 5  is a schematic view showing how a conventional thin part in which the plurality of slits  124  is not formed and which is not curved in a wavy shape (is formed in a flat plate) is transformed. 
       FIG. 6  is a schematic view showing how the thin part  121  according to an embodiment of the present invention is transformed. 
     In  FIGS. 5 and 6 , a point at which the inversion plate and the thin part of the collecting plate are connected to each other is indicated by A, and in the order of time series, A0, A1 and A2 are illustrated. 
     Moreover, any point on the conventional thin part is indicated by B, and in the order of time series, B0, B1 and B2 are illustrated. 
     Moreover, any point on the thin part  121  is indicated by C, and in the order of time series, C0, C1 and C2 are illustrated. 
     As shown in  FIG. 5 , in the conventional thin part, the locus of the point A and the locus of the point B are substantially parallel. 
     In order for the point B to move nonparallel to the locus of the point A, the distance (radial length) from the center of the thin part to the point B needs to change, and the circumferential length of the thin part at the point B needs to change. Realizing this needs a large amount of energy. 
     In general, since transformation makes progress so that energy therefor is a minimum, the conventional thin part is transformed so that the locus of the point A and the locus of the point B are substantially parallel. 
     As shown in  FIGS. 6(   a ) and  6 ( b ), in the thin part  121  according to an embodiment of the present invention, the opening and closing of the plurality of slits  124  formed in the thin part  121  absorb circumferential distortion of the thin part  121 , and thereby the point C can move radially outward of the thin part  121 . In other words, the opening and closing of the plurality of slits  124  formed in the thin part  121  change the circumferential length of the thin part  121  at the point C, and change the distance (radial length) from the center of the thin part  121  to the point C. 
     This makes it possible to, when the thin part  121  is transformed, easily stretch the wavy part thereof, and to greatly reduce the stress generated on. 
     Therefore, it is possible to greatly suppress fatigue of the carved part  123  of the thin part  121  which is to be accumulated in the case where the pressure in the case  20  increases and decreases at a relatively low level due to variation of temperature of the battery  1  in use, and the like. Consequently, it is possible to greatly suppress time degradation of the CID  100 . 
     In  FIG. 7 , shown are results obtained by analyzing, by means of CAE, the stress generated on the carved part  123  of the thin part  121  according to an embodiment of the present invention, and the stress generated on the conventional carved part of the thin part. 
       FIG. 7  shows a relationship between the pressure in the case of the battery and the stress generated on the carved part of the thin part. 
     As shown in  FIG. 7 , in the case where the pressure in the case of the battery is a predetermined value (P in  FIG. 7 ) before the carved part of the thin part is ruptured, the stress generated on the carved part  123  of the thin part  121  according to an embodiment of the present invention is smaller than the stress generated on the conventional carved part of the thin part. 
     Therefore, it was found that the thin part  121  according to an embodiment of the present invention could reduce the stress generated on the carved part  123 . 
     In the present embodiment, the thin part  121  has the carved part  123  continuously formed in the circumferential direction thereof, but a configuration of the thin part  121  is not limited thereto. 
     For example, as shown in  FIG. 8 , a thin part  221  in which a plurality of carved parts  223  is intermittently formed may be used as a thin part according to an embodiment of the present invention. 
     In this case, it is preferable that the same number of slits  224  as the plurality of carved parts  223  are formed, and are arranged to perpendicularly intersect with the respective carved parts  223 . 
     It is more preferable that, as shown in  FIG. 9 , a pair of slits  224  is formed in the vicinities of both ends of each carved part  223 , and each pair of slits  224  is arranged to perpendicularly intersect with each carved part  223 . 
     This makes it possible to inhibit stress from being unevenly generated on the thin part  221  due to difference between rigidity of the part, on which the carved parts  223  is formed, of the thin part  221 , and rigidity of the part, on which the carved parts  223  is not formed, of the thin part  221 . Specifically, cracks are formed so as to connect the adjacent carved parts  223  when each slit  224  opens, thus enabling to bring the rigidity of the part, on which the carved parts  223  is not formed, of the thin part  221  close to the rigidity of the part thereof on which the carved parts  223  is formed, and to even the stress on the thin part  221 . 
     Moreover, in the present embodiment, the thin part  121  has the carved part  123  in the shape of a perfect circle, but a configuration of the thin part  121  is not limited thereto. 
     For example, as shown in  FIG. 10 , a thin part  321  having a carved part  323  in the shape of an ellipse may be used as a thin part according to an embodiment of the present invention. In this case, it is preferable that a plurality of slits  324  is formed to perpendicularly intersect with the carved part  323 . 
     In the present embodiment, the twelve slits  124  are formed in the thin part  121 . However, the number of the slits  124  is not limited thereto, and is set to a suitable number for reducing the stress generated on the carved part  123  of the thin part  121 . 
     Moreover, in the present embodiment, the slits  124  are formed to intersect with the carved part  123 , but may be formed not to intersect with the carved part  123  as long as the slits  124  are arranged in the vicinity of the carved part  123 . 
     However, in order to suitably reduce the stress generated on the carved part  123  of the thin part  121 , it is preferable that the slits  124  are formed to intersect with the carved part  123 . 
     Moreover, in the present embodiment, the slits  124  are formed to be perpendicular to the carved part  123 , but may be formed not to be perpendicular to the carved part  123 . 
     However, in order to suitably reduce the stress generated on the carved part  123  of the thin part  121 , it is preferable that the slits  124  are formed to be perpendicular to the carved part  123 . 
     Moreover, in the present embodiment, the plurality of slits  124  is radially arranged at equal intervals, but a configuration of the plurality of slits  124  is not limited thereto. 
     However, in view of removing unevenness of the stress generated on the carved part  123  of the thin part  121 , it is preferable that the plurality of slits  124  is radially arranged at equal intervals. 
     Moreover, in the present embodiment, each of the slit  124  is formed in a straight line. However, each of the slit  124  may be formed in a curved line as long as the plurality of slits  124  can open to reduce the stress generated on the carved part  123  of the thin part  121 . 
     In the present embodiment, the battery  1  is a cylindrical battery, but a square battery may be used as a sealed battery according to an embodiment of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applied to a sealed-type secondary battery having a current interrupt device for interrupting a current in emergency. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 : battery 
               10 : electrode body 
               20 : case 
               21 : storage part 
               22 : lid part 
               100 : CID 
               110 : inversion plate 
               111 : carved part 
               120 : collecting plate 
               121 : thin part 
               122 : fitting hole 
               123 : carved part 
               124 : slit