Patent Publication Number: US-2015064550-A1

Title: Prismatic secondary cell

Description:
TECHNICAL FIELD 
     The present invention relates to a prismatic secondary cell that is used, for example, as a vehicle-mounted secondary cell. 
     BACKGROUND ART 
     In recent years, a lithium-ion secondary cell having a high energy density is increasingly developed as a power source for electric vehicles and the like. Although there are variously shaped lithium-ion secondary cells, a prismatic secondary cell is used as a vehicle-mounted cell because it has high volumetric efficiency. For example, a structure disclosed, for instance, in Patent Literature 1 is such that a flatly wound electrode group is housed in a deep drawn cell can with a winding axis placed in a horizontal position. In this structure, the cell can is provided with an opening into which a group of electrical power generating elements is inserted. The opening is sealed with a cell lid. A through-hole is made in the cell lid to inject an electrolytic solution into the cell can. After the opening in the cell can is sealed with the cell lid, the electrolytic solution can be injected with a solution injection nozzle inserted into the through-hole. After the electrolytic solution is injected, the through-hole is sealed with a plug. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2011-165436 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     According to the structure described in Patent Literature 1, there is only one through-hole. Therefore, when the electrolytic solution is to be injected, an opening for allowing air in the cell canto escape is limited to a gap between a solution injection hole and a solution injection nozzle. It means that the electrolytic solution does not readily enter the cell can. Further, a film of electrolytic solution may be formed over the air escape opening to splash the electrolytic solution. Moreover, if a total of two through-holes are made for solution injection and for air discharge, they need to be sealed with two plugs. 
     The present invention has been made in view of the above circumstances. An object of the present invention is to provide a prismatic secondary cell having a structure that makes it easy to inject an electrolytic solution into a cell can and seal the cell can. 
     Solution to Problem 
     The configuration defined in the appended claims is adopted to solve the above problem. The present invention includes a plurality of means for solving the above problem. According to an exemplary means included in the present invention, there is provided a prismatic secondary cell in which an electrode group is housed in a cell can and an opening in the cell can is sealed with a cell lid. The prismatic secondary cell includes a solution injection section and a plug section. The solution injection section has a plurality of through-holes that penetrate the cell lid and are positioned adjacent to each other. The plug section integrally seals the through-holes in the solution injection section. 
     Advantageous Effects of Invention 
     The present invention provides a prismatic secondary cell having a structure that makes it easy to inject an electrolytic solution and seal. Problems, configurations, and advantageous effects other than described above will become apparent from the following description of embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view illustrating a prismatic secondary cell according to a first embodiment of the present invention. 
         FIG. 2  is an exploded perspective view illustrating the prismatic secondary cell according to the first embodiment. 
         FIG. 3A  is an enlarged plan view illustrating essential parts of the prismatic secondary cell according to the first embodiment. 
         FIG. 3B  is a cross-sectional view taken along line A 1 -A 1  of  FIG. 3A . 
         FIG. 4  is a cross-sectional view illustrating a state where a solution injection section is sealed with a plug. 
         FIG. 5  is a conceptual diagram illustrating a solution injection process according to the first embodiment. 
         FIG. 6A  is an enlarged plan view illustrating essential parts of the secondary cell according to a second embodiment of the present invention. 
         FIG. 6B  is a cross-sectional view taken along line A 2 -A 2  of  FIG. 6A . 
         FIG. 7  is a cross-sectional view illustrating a state where an injection nozzle is inserted into an injection through-hole in the solution injection section. 
         FIG. 8A  is an enlarged plan view illustrating essential parts of the secondary cell according to a third embodiment of the present invention. 
         FIG. 8B  is a cross-sectional view taken along line A 3 -A 3  of  FIG. 8A . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A prismatic secondary cell according to the present embodiment is configured so that an electrode group is housed in a cell can and that an opening in the cell can is sealed with a cell lid. The prismatic secondary cell includes a solution injection section and a plug section. The solution injection section has a plurality of through-holes that penetrate the cell lid and are positioned adjacent to each other. The plug section integrally seals the through-holes in the solution injection section. 
     First Embodiment 
     The configuration of the prismatic secondary cell according to a first embodiment of the present invention will now be described with reference to the accompanying drawings. For the sake of convenience, the following description is given on the assumption that a cell lid  3  side of the prismatic secondary cell  1  is referred to as the upper side, and that a bottom side of a cell can  2  is referred to as the lower side. However, it does not specifically define the attitude of the prismatic secondary cell  1 . 
       FIG. 1  illustrates the overall configuration of the prismatic secondary cell according to the first embodiment.  FIG. 2  is an exploded perspective view illustrating the prismatic secondary cell shown in  FIG. 1 . 
     The prismatic secondary cell  1  is a lithium-ion secondary cell that includes the cell can  2  and the cell lid  3  as shown in  FIGS. 1 and 2 . The cell can  2  is shaped like a rectangular box having an oblong bottom wall surface PB, a pair of wide side wall surfaces PW, and a pair of narrow side wall surfaces PN. The pair of wide side wall surfaces PW are bent at two long sides of the bottom wall surface PB to face each other. The pair of narrow side wall surfaces PN are bent at two end sides of the bottom wall surface PB to face each other. The top of the cell can  2  is provided with a rectangular opening  2   a , which is upwardly open. 
     The cell can  2  houses a later-described electrode group  4 . The opening  2   a  in the cell can  2  is sealed with the cell lid  3 . The cell lid  3 , which is flat and rectangular in shape, entirely covers the opening  2   a  in the cell can  2 , which is between the upper ends of the pair of wide side wall surfaces PW and the upper ends of the pair of narrow side wall surfaces PN. The cell can  2  and cell lid  3  are formed of an aluminum alloy and laser-welded liquid-tight to form a hermetically-closed container shaped like a rectangular parallelepiped. 
     A positive terminal  5 A and a negative terminal  5 B are attached to the cell lid  3  through an insulating member. The positive terminal  5 A and the negative terminal  5 B are positioned apart from each other and arranged in the direction of the long side of the cell lid  3 . More specifically, the positive terminal  5 A is disposed toward one side of the cell lid  3  and the negative terminal  5 B is disposed toward the other end. Electrical power is supplied from the electrode group  4  to an external load through the positive and negative terminals  5 A,  5 B. Further, externally generated electrical power is charged into the electrode group  4  through the positive and negative terminals  5 A,  5 B. 
     A gas discharge valve  6  and a solution injection section  7  are attached to the cell lid  3  in addition to the positive and negative terminals  5 A,  5 B. The gas discharge valve  6  is disposed at the longitudinal center of the cell lid  3 . The solution injection section  7  is disposed between the gas discharge valve  6  and the negative terminal  5 B. 
     When the pressure in a cell container rises above a predetermined value, the gas discharge valve  6  opens to discharge a gas in the cell container and reduce the pressure in the cell container for the purpose of assuring the safety of the prismatic secondary cell  1 . 
     The solution injection section  7  is used to inject an electrolytic solution into the cell can  2  after the opening  2   a  in the cell can  2  is sealed with the cell lid  3 . A solution injection nozzle  101  (see  FIG. 5 ) is used to inject the electrolytic solution. After the electrolytic solution is injected into the cell can  2 , the solution injection section  7  is sealed with the plug section  8 . 
     The solution injection section  7  has a plurality of through-holes that penetrate the cell lid  3  and are positioned adjacent to each other. The present embodiment includes a large-diameter through-hole and a small-diameter through-hole as the through-holes. The large-diameter through-hole has a larger diameter than the small-diameter through-hole. The large-diameter through-hole is used as an injection through-hole  21  for injecting the electrolytic solution into the cell can  2 . The small-diameter through-hole is used as an air discharge through-hole  22  for discharging air. The injection through-hole  21  and the air discharge through-hole  22  are blocked up by one plug  31  (see  FIG. 3 ) that forms the plug section  8 . 
     The cell can  2  of the prismatic secondary cell  1  houses the electrode group  4  as shown in  FIG. 1  with an insulating sheet  9  positioned between the cell can  2  and the electrode group  4 . The electrode group  4  is formed by winding positive and negative electrodes with a separator placed in between. The electrode group  4  is flat in shape and has a pair of wide surfaces and a pair of narrow surfaces. A positive electrode connection section  4 A including an exposed positive electrode metal foil section is formed at one end in the direction of a winding axis of the electrode group  4 . A negative electrode connection section  4 B including an exposed negative electrode metal foil section is formed at the other end in the direction of the winding axis of the electrode group  4 . 
     The positive electrode connection section  4 A is connected to the positive terminal  5 A through a positive electrode current collector plate  11 A. The negative electrode connection section  4 B is connected to the negative terminal  5 B through a negative electrode current collector plate  11 B. One end of the positive electrode current collector plate  11 A is connected to the positive terminal  5 A, and the other end is extended toward the bottom of the cell can  2  from the positive terminal  5 A and connected to the positive electrode connection section  4 A. One end of the negative electrode current collector plate  11 B is connected to the negative terminal  5 B, and the other end is extended toward the bottom of the cell can  2  from the negative terminal  5 B and connected to the negative electrode connection section  4 B. 
     The positive terminal  5 A and the positive electrode current collector plate  11 A are formed of an aluminum alloy, and the negative terminal  5 B and the negative electrode current collector plate  11 B are formed of a copper alloy. The positive terminal  5 A and the positive electrode current collector plate  11 A and the negative terminal  5 B and the negative electrode current collector plate  11 B are electrically insulated from the cell lid  3  because insulating seal members (gaskets)  12 A,  12 B and insulating members  13 A,  13 B are disposed between the cell lid  3  and the positive terminal  5 A and the positive electrode current collector plate  11 A and the negative terminal  5 B and the negative electrode current collector plate  11 B. Through-holes  3   a ,  3   b , which engage with the insulating seal members (gaskets)  12 A,  12 B, are made in the cell lid  3 . 
     The configurations of the solution injection section  7  and the plug section  8  will now be described in detail with reference to  FIGS. 3A ,  3 B, and  4 . 
     As shown in  FIGS. 3A and 3B , the solution injection section  7  has a concave portion  23  that is formed on the front surface  3   c  of the cell lid  3 . As shown in  FIG. 3A , the concave portion  23  is elliptically shaped as viewed from above. The longitudinal axis of the ellipse is positioned in the direction of the long side of the cell lid  3 . As shown in  FIG. 3B , the concave portion  23  has a fixed depth, an elliptical side wall surface  23   a , and a planar bottom surface  23   b . The upper end of the injection through-hole  21  and the upper end of the air discharge through-hole  22  are open in the bottom surface  23   b  of the concave portion  23 . The lower end of the injection through-hole  21  and the lower end of the air discharge through-hole  22  are open in the back surface  3   d  of the cell lid  3 . 
     The injection through-hole  21  and the air discharge through-hole  22  are positioned so that the bottom surface  23   b  of the concave portion  23  exists on the whole circumference of the upper end of the injection through-hole  21  and of the upper end of the air discharge through-hole  22 . In other words, the upper end of the injection through-hole  21  and the upper end of the air discharge through-hole  22  are open so that the bottom surface  23   b  is positioned between such through-holes  21 ,  22  and the side wall surface  23   a  of the concave portion  23 . 
     Therefore, when the plug  31  of the later-described plug section  8  is attached to the concave portion  23 , the lower surface  31   a  of the plug  31  comes into contact with the bottom surface  23   b  of the concave portion  23  to exhibit highly-reliable hermetic sealing performance. The outer surface of the injection through-hole  21  or of the air discharge through-hole  22  may be in internal contact with the side wall surface  23   a  of the concave portion  23 . 
     The injection through-hole  21  needs to have a larger diameter than the leading end of the solution injection nozzle  101  (see  FIG. 5 ). It is preferred that the gap between the injection through-hole  21  and the solution injection nozzle  101  be small in order, for instance, to prevent the leakage of the electrolytic solution. 
     The injection through-hole  21  has a larger diameter than the air discharge through-hole  22  in order to smoothly inject a large amount of electrolytic solution within a short period of time. The injection through-hole  21  and the air discharge through-hole  22  are disposed adjacent to each other in the longitudinal axis direction of the ellipse of the concave portion  23 . Further, the injection through-hole  21  is disposed near a narrow side wall surface PN of the cell can  2 . Therefore, the electrolytic solution injected from the solution injection nozzle  101  can be positively directed toward the bottom of the cell can  2  and stored in the cell can  2 . 
     After the electrolytic solution is injected, the injection through-hole  21  and the air discharge through-hole  22  are integrally sealed by the plug section  8 . The plug section  8  is formed of a single plug  31 . The plug  31  is formed of a plate-like member that is elliptically shaped as viewed from above and capable of engaging with the concave portion  23 . The plug  31  includes a lower surface  31   a , an outer surface  31   b , and an upper surface  31   c . The lower surface  31   a  comes into contact with the bottom surface  23   b  of the concave portion  23  to block up both the injection through-hole  21  and the air discharge through-hole  22  when the plug  31  is engaged with the concave portion  23 . The outer surface  31   b  opposes the side wall surface  23   a  of the concave portion  23 . The upper surface  31   c  is flush with the front surface  3   c  of the cell lid  3 . 
     The plug  31  is engaged with the concave portion  23  and welded to the cell lid  3  so that a weld zone w is formed along the whole circumference of the outer surface  31   b . As shown in  FIG. 4 , the plug  31  is welded while the lower surface  31   a  of the plug  31  is in planar contact with the bottom surface  23   b  of the concave portion  23 . Therefore, a large area is in planar contact. Further, the bottom surface  23   b  of the concave portion  23  exists along the whole circumference of the upper end of the injection through-hole  21  and of the upper end of the air discharge through-hole  22 . Therefore, the lower surface  31   a  of the plug  31  can be brought into planar contact with the whole circumference of the upper end of the injection through-hole  21  and of the upper end of the air discharge through-hole  22 . This results in highly-reliable hermetic sealing performance. 
     An electrolytic solution injection process according to the present embodiment will now be described with reference to  FIG. 5 . 
     The electrolytic solution is injected into the cell can  2  by using a solution injection nozzle  101 . The cell can  2  to which the cell lid  3  is welded is set in a solution injection device (not shown), and the leading end of the solution injection nozzle  101  is inserted into the injection through-hole  21 . In such an instance, the vertical position of the solution injection nozzle  101  is adjusted so that the leading end of the solution injection nozzle  101  does not come into contact with the electrode group  4  in the cell can  2 . The solution injection nozzle  101  is coupled, for instance, with a piping to a tank (not shown), which stores the electrolytic solution, and to a syringe (not shown), which controls an electrolytic solution discharge speed and a solution injection amount. The electrolytic solution is discharged from the leading end of the solution injection nozzle  101  and injected into the cell can  2 . 
     The electrolytic solution injected into the cell can  2  from the solution injection nozzle  101  flows along the gap between the electrode group  4  and the cell can  2  and toward the bottom of the cell can  2 , and is stored in the cell can  2 . The solution injection amount is adjusted to provide a solution level that immerses the electrode group  4 . 
     The gap between the wide side wall surfaces PW of the cell can  2  and the wide surfaces of the electrode group  4  is narrower than the gap between the narrow side wall surfaces PN of the cell can  2  and the narrow surfaces on opposing sides in the direction of the winding axis of the electrode group  4 . Hence, most of the electrolytic solution injected into the cell can  2  from the solution injection nozzle  101  flows in two different directions as shown in  FIG. 5  when it reaches the upper surface of the electrode group  4 , and then flows along the upper surface of the electrode group  4  and toward the narrow side wall surfaces PN on opposing sides in the direction of the width of the cell can  2 . Eventually, the electrolytic solution passes through the gap between the narrow side wall surfaces PN of the cell can  2  and the narrow surfaces of the electrode group  4 , flows toward the bottom of the cell can  2 , and is stored in the cell can  2 . 
     In the present embodiment, the injection through-hole  21  is disposed closer to a narrow side wall surface PN of the cell can  2  than the air discharge through-hole  22 . Therefore, the electrolytic solution injected from the solution injection nozzle  101  can be positively directed toward the bottom of the cell can  2  and promptly injected into the cell can  2 . 
     In order to steadily inject the electrolytic solution into the cell can  2  within a short period of time, it is preferred that air replaced by the electrolytic solution in the cell can  2  be efficiently discharged out of the cell can  2 . If the air is not adequately discharged, the electrolytic solution is not smoothly injected into the cell can  2 . As a result, the electrolytic solution scatters out of the cell can  2 . This causes the solution injection amount to vary. Further, if the scattered electrolytic solution remains in the concave portion  23  of the cell lid  3 , the remaining electrolytic solution may evaporate when an attempt is made to weld the plug  31  to the cell lid  3 . This may result in improper welding. 
     In the present embodiment, the air discharge through-hole  22  is disposed adjacent to the injection through-hole  21 . Hence, the air in the cell can  2  passes through the air discharge through-hole  22  and is forced out of the cell can  2 . Consequently, the electrolytic solution can be smoothly injected into the cell can  2 . This makes it possible to prevent the electrolytic solution from scattering out of the cell can  2  and stabilize the solution injection amount. Further, the electrolytic solution can be prevented from scattering and attaching to the concave portion  23  of the cell lid  3 . This makes it possible to eliminate the cause of improper welding of the plug  31 . 
     The solution injection section  7  is sealed with one plug  31  during a single process. The plug  31  is engaged with the concave portion  23  so that the lower surface  31   a  of the plug  31  is brought into planar contact with the bottom surface  23   b  of the concave portion  23 . The whole circumference of the outer surface  31   b  of the plug  31  is then laser-welded to the whole circumference of the side wall surface  23   a  of the concave portion  23 . 
     According to the prismatic secondary cell  1  having the above-described configuration, the electrolytic solution can be smoothly injected because the solution injection section  7  has the injection through-hole  21  and the air discharge through-hole  22 . Further, the plug  31  is engaged with the concave portion  23  of the solution injection section  7  so that both the injection through-hole  21  and the air discharge through-hole  22  are blocked up integrally with the single plug  31 . This makes it easy to seal the solution injection section  7 . 
     In the present embodiment, positioning markings  32 ,  33  for image recognition are put on the upper surface  31   c  of the plug  31  and the front surface  3   c  of the cell lid  3 , respectively, in order to ensure that the plug  31 , which is elliptically shaped as viewed from above, is precisely engaged with the concave portion  23  of the cell lid  3  by using an automatic labor-saving device. 
     Further, in the present embodiment, the concave portion  23  is elliptically shaped as viewed from above. Alternatively, however, the concave portion  23  may be shaped like an athletic running track, a rectangle, or a polygon. The outer shape of the concave portion  23  is not limited to that described in conjunction with the present embodiment. 
     Moreover, in the present embodiment, the injection through-hole  21  has a larger diameter than the air discharge through-hole  22 . The reason is that the injection through-hole  21  is inevitably larger in diameter than the air discharge through-hole  22  by the wall thickness of the solution injection nozzle  101  as far as the cross-sectional area of the discharge hole in the solution injection nozzle  101  is assumed to be substantially the same as the area of the opening in the air discharge through-hole  22 . Hence, the diameters of the injection through-hole  21  and the air discharge through-hole  22  are not limited to those described in conjunction with the present embodiment. For example, the air discharge through-hole  22  may be larger in diameter than the injection through-hole  21 . Besides, the air discharge through-hole  22  may be shaped like a rectangle or a polygon instead of being circular in shape. 
     Second Embodiment 
     A second embodiment of the present invention will now be described with reference to  FIGS. 6A ,  6 B, and  7 . Elements identical with those of the first embodiment are designated by the same reference signs and will not be redundantly described in detail. 
     The second embodiment is characteristically configured so that the solution injection section  7  has a convex portion  3   e , which is formed on the back surface of the cell lid  3 , and that the lower end of the injection through-hole  21  is open to the leading end of the convex portion  3   e , and further that the lower end of the air discharge through-hole  22  is open to the back surface of the cell lid  3 . 
     As shown in  FIGS. 6A and 6B , the solution injection section  7  has the injection through-hole  21  and the air discharge through-hole  22 . The injection through-hole  21  and the air discharge through-hole  22  are disposed adjacent to each other. The upper ends of these through-holes  21 ,  22  are open to the bottom surface  23   b  of the concave portion  23 . 
     Although the lower end of the air discharge through-hole  22  is open to the back surface of the cell lid  3 , the lower end of the injection through-hole  21  is open to the leading end of the convex portion  3   e  formed on the back surface  3   d  of the cell lid  3 . Hence, the lower end of the injection through-hole  21  is positioned below the lower end of the air discharge through-hole  22 . 
     If, for instance, the discharge speed of the electrolytic solution, which is to be discharged from the solution injection nozzle  101  inserted into the injection through-hole  21 , is increased in order to reduce the time required for the solution injection process, it is anticipated that the electrolytic solution may scatter in the cell can  2 . In the present embodiment, the lower end of the injection through-hole  21  is positioned below the lower end of the air discharge through-hole  22  as shown in  FIG. 7  to provide a height difference between the lower ends of the two through-holes. Therefore, the electrolytic solution discharged from the solution injection nozzle  101  can be effectively prevented from scattering toward the air discharge through-hole  22 . This makes it possible to steadily discharge the air in the cell can  2  from the air discharge through-hole  22  and steadily inject the electrolytic solution. 
     Third Embodiment 
     A third embodiment of the present invention will now be described with reference to  FIGS. 8A and 8B . Elements identical with those of the foregoing embodiments are designated by the same reference signs and will not be redundantly described in detail. 
     The third embodiment is characteristically configured so that the shapes of the concave portion  23  and the plug  31 , which are elliptical in the second embodiment, are changed to circular, and that the injection through-hole  21  is disposed at the center of the circle of the concave portion  23 , and further that the air discharge through-hole  22  is disposed beside the injection through-hole  21 . 
     In the present embodiment, two units of the air discharge through-hole  22  are disposed apart from each other in the direction of the long side of the cell lid  3  with the injection through-hole  21  positioned in between. It means that the number of units of the air discharge through-hole  22  is larger than in the second embodiment. In other words, the air can be discharged in a plurality of directions. 
     Consequently, the air in the cell can  2  can be steadily discharged. This makes it possible to steadily inject the electrolytic solution. Further, as the plug  31  is circular in shape, it can be more easily formed than the elliptically shaped plug. Furthermore, when the plug  31  is to be engaged with the concave portion  23 , its orientation need not be adjusted for the concave portion  23 . Hence, the plug  31  can easily be engaged with the concave portion  23 . Although  FIG. 8  indicates that the plug  31  is circular in shape, it may be elliptically shaped. 
     While the embodiments of the present invention have been described above, the present invention is not limited to the forgoing embodiments, but extends to various modifications based on design changes that fall within the spirit and scope of the appended claims. For example, the foregoing preferred embodiments are described in detail for better understanding of the present invention. The present invention is not limited to embodiments that include all the elements described above. Some elements of an embodiment may be replaced by some elements of another embodiment or some elements of an embodiment may be added to the elements of another embodiment. Further, some elements of an embodiment may be subjected to the addition of other elements, deleted, or replaced by other elements. 
     LIST OF REFERENCE SIGNS 
     
         
           1  . . . Prismatic secondary cell 
           2  . . . Cell can 
           3  . . . Cell lid 
           3   e  . . . Convex portion 
           4  . . . Electrode group 
           7  . . . Solution injection section 
           8  . . . Plug section 
           21  . . . Injection through-hole (large-diameter through-hole) 
           22  . . . Air discharge through-hole (small-diameter through-hole) 
           23  . . . Concave portion 
           31  . . . Plug 
           32 ,  33  . . . Positioning marking