Abstract:
An inter-connector interposed between two serially connected unit cells provides mechanical strength and conductivity to the serial connection between the unit cells. Embodiments of the inter-connector comprise a supporting frame providing mechanical support for the two unit cells; a welding projection for welding the interconnector to a unit cell; and a welding projection surrounding area located between the welding projection and the supporting frame, wherein the supporting frame is thicker than the welding projection surrounding area, and the welding projection is thicker than the welding projection surrounding area.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2007-7976, filed on Jan. 25, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     This disclosure relates to an inter-connector that is interposed between two serially connected unit cells to provide mechanical strength to and to conductively couple a serial connection between unit cells. 
     2. Discussion of Related Art 
     In general, alkali storage batteries—such as nickel-hydride storage batteries, nickel-cadmium storage batteries, etc. or lithium-based storage batteries such as lithium-ion cell, lithium-polymer cell, etc.—are generally manufactured by interposing separators between cathodes and anodes, then helically winding them; coupling current collectors to the ends of the cathodes and the anodes to form electrodes, disposing the electrodes within metallic outer cases, welding lead portions extending from the current collectors to seals; and mounting the seals on openings of the outer cases while interposing insulating gaskets therebetween. Because such an alkali storage battery requires a high output when used for example, as a power source for an electric motor tool or for an electric automobile, etc., storage batteries, have generally been assembled into module cells made by connecting a plurality of individual cells in series. Where storage batteries are used in high output applications, such as powering a large electric motor or an electric automobile, the module cell comprising a plurality of cylindrical unit cells coupled in serial and/or in parallel have been used. 
       FIG. 1  shows in perspective a plane-frame module cell  10  comprising a parallel arrangement of cylindrical serial cells  30  in a frame  20 , the cylindrical serial cells  30  being formed by serially connecting a predetermined number of the cylindrical unit cells  40 . Although only a lower frame receiving the cylindrical serial cells  30  is shown in the  FIG. 1 , there may also be one or more upper frames having structure similar to that of the lower frame stacked therein. 
     In the cylindrical serial cells  30  shown, a serial inter-connector is interposed between the two serial unit cells  40 , forming a serial interface that mechanically and electrically couples the two unit cells  40 . When coupling unit cells  30  using an inter-connector, the inter-connector is typically welded to the cathode terminal surface of one unit cell  40  and the outer wall of the other unit cell  40 . 
     Contact resistance welding is commonly used in coupling the inter-connector to the cells because it is useful for welding small objects. Contact resistance welding has some drawbacks, however. To obtain a good quality weld, a welding electrode is preferably contacted with the inter-connector during the welding process. In the serial interface between unit cells  40 , welds to the cathode terminal surface or the outer wall of the unit cell are formed from melted portions of the inter-connector. The inter-connector should have sufficient thickness to securely hold the two unit cells together. If the inter-connector is thicker than the outer wall of the unit cell, the current from a welding electrode contacting the inter-connector flows through the inter-connector instead of to the outer wall of the unit cell. Consequently, at best, a poor weld is formed between the inter-connector and unit cell. 
     Typically the outer wall of a unit cell is not very thick, for example, from about 0.4 T to about 0.5 T. In general, the side wall of the unit cell is about 0.4 T thick and the bottom is about 0.5 T thick. Here, 1 T corresponds to about 1 mm. An inter-connector thinner than the unit-cell outer wall may not have sufficient strength to secure the two unit cells unless expensive metal materials are used in the inter-connector. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention solve at least one above problems. Some embodiments provide an inter-connector for unit cells having excellent weldability to the unit cell, combined with sufficient strength, as well as a serial cell comprising the same. 
     Some embodiments provide an inter-connector for unit cells with low cost, excellent weldability, and excellent mechanical strength, as well as a serial cell comprising the same. 
     Some embodiments provide an inter-connector comprising: a supporting frame providing mechanical strength in order to fix two unit cells; a welding projection to be welded to the unit cells in a contact resistance welding manner; and a welding projection surrounding area located between the welding projection and the supporting frame, wherein the thickness of the supporting frame is thicker than that of the welding projection surrounding area and the thickness of the welding projection is thicker than that of the welding projection surrounding area. Comparing the thickness of the welding projection and the welding projection surrounding area with that of the outer wall of the unit cell, it is preferable to make the thickness of the supporting frame thicker than that of the outer wall of the unit cell and the thickness of the welding projection surrounding area equal to or thinner than that of the outer wall of the unit cell. 
     Other embodiments provide an inter-connector connecting a first unit cell to a second unit cell in series comprising: a fixing wall having the outer wall of the first unit cell inserted into the inside thereof and a first welding projection to be welded to the first unit cell in a contact resistance welding manner; a first supporting surface successively formed on the fixing wall and supporting a second electrode surface of the first unit cell; and a second supporting surface supporting a first electrode surface of the second unit cell, wherein the thickness of at least welding projection surrounding area in the fixing wall is equal to or thinner than that of the anode outer wall of the unit cell. 
     Other embodiments provide an inter-connector connecting a first unit cell to a second unit cell in series comprising: a fixing wall having the outer wall of the first unit cell inserted into the inside thereof; a first supporting surface successively formed on the fixing wall and supporting a second electrode surface of the first unit cell; and a second supporting surface supporting a first electrode surface of the second unit cell and having a welding projection to be welded to the second unit cell in a contact resistance welding manner, wherein the thickness of at least welding projection surrounding area in the second supporting surface is equal to or thinner than that of the anode outer wall of the unit cell. 
     Embodiments of a serial cell equipped the inter-connector further comprise: two or more unit cells; and an inter-connector connecting a first unit cell and a second unit cell between the lower part of the first unit cell of the two or more unit cells and the upper part of the second unit cell neighboring the first unit cell. Embodiments of the inter-connector comprise: a supporting frame providing mechanical strength in order to fix the first unit cell and the second unit cell; a welding projection to be welded to the first unit cell or the second unit cell; and a welding projection surrounding area located between the welding projection and the supporting frame, wherein the thickness of the supporting frame is thicker than that of the welding projection surrounding area and the thickness of the welding projection is thicker than that of the welding projection surrounding area. 
     Some embodiments provide an inter-connector comprising: a supporting frame dimensioned and configured to mechanically couple two unit cells; a welding projection operable to be welded to the unit cells; and a welding projection surrounding area disposed between the welding projection and the supporting frame. At least a portion of the supporting frame is thicker than the welding projection surrounding area, and at least a portion of the welding projection is thicker than the welding projection surrounding area. 
     In some embodiments, the at least a portion of the supporting frame is thicker than an outer wall of a unit cell and a thickness of the welding projection surrounding area equal to or thinner than the outer wall of the unit cell. In some embodiments, a ratio of a height to a width of the welding projection is from about 15% to about 20%. 
     In some embodiments, the two unit cells comprise a first unit cell and a second unit cell, and the inter-connector is dimensioned and configured to couple the first unit cell to the second unit cell in series. In some embodiments, the supporting frame comprises: a fixing wall dimensioned and configured to receive a portion of the first unit cell; a first supporting surface formed on the fixing wall dimensioned and configured to support a surface of an electrode of the first unit cell; and a second supporting surface dimensioned and configured to contact and support a surface of an electrode of the second unit cell. In some embodiments, the welding projection comprises a first welding projection extending inwardly from the fixing wall, and operable to be welded to the first unit cell. 
     In some embodiments, the electrode surface of the first unit cell comprises an anode, and the electrode surface of the second unit cell comprises a cathode, at least a portion of the fixing wall is thicker than an anode outer wall of the first unit cell, and a thickness of the first welding projection surrounding area is equal to or thinner than the anode outer wall of the first unit cell. In some embodiments, the electrode surface of the first unit cell comprises an anode, the electrode surface of the second unit cell comprises a cathode, and a thickness of the fixing wall is equal to or thinner than that of an anode outer wall of the unit cell. 
     In some embodiments, the welding projection comprises a second welding projection formed on the second supporting surface, and operable to be welded to the second unit cell. In some embodiments, the electrode surface of the first unit cell comprises an anode, and the electrode surface of the second unit cell comprises a cathode, a thickness of the second welding projection surrounding area is equal to or thinner than the cathode outer wall of the second unit cell. 
     In some embodiments, at least a portion of the supporting frame is disposed between the first supporting surface and the second supporting surface, thereby forming a step difference between the first supporting surface and the second supporting surface. 
     An inter-connector for connecting a first unit cell to a second unit cell in series, the inter-connector comprising: a fixing wall dimensioned and configured to receive an outer wall of a first unit cell therein, and comprising a first welding projection operable to be welded to the first unit cell; a first supporting surface formed on the fixing wall, and dimensioned and configured to support an electrode surface of the first unit cell; and a second supporting surface dimensioned and configured to support an electrode surface of the second unit cell, wherein the thickness of a welding projection surrounding area of the fixing wall is equal to or thinner than an anode outer wall of a unit cell. 
     Some embodiments further comprise a step wall disposed between the first supporting surface and the second supporting surface, thereby forming a step between the first supporting surface and the second supporting surface. 
     In some embodiments, the electrode surface of the first unit cell comprises an anode, and the electrode surface of the second unit cell comprises a cathode. In some embodiments, a ratio of a height to a width of the first welding projection is from about 15% to about 20%. In some embodiments, the second supporting surface comprises a second welding projection operable to be welded to the second unit cell. 
     Some embodiments provide an inter-connector for connecting a first unit cell to a second unit cell in series, the inter-connector comprising: a fixing wall dimensioned an configured to receive an outer wall of a first unit cell therein; a first supporting surface formed on the fixing wall, and dimensioned and configured to support an electrode surface of the first unit cell; and a second supporting surface dimensioned and configured to support an electrode surface of a second unit cell, the second supporting surface comprising a welding projection operable to be welded to the second unit cell, wherein the thickness of a welding projection surrounding area of the second supporting surface is equal to or thinner than an anode outer wall of a unit cell. 
     Some embodiments further comprise a step wall disposed between the first supporting surface and the second supporting surface, thereby generating a step between the first supporting surface and the second supporting surface. 
     In some embodiments, the electrode surface of the first unit cell comprises an anode, and the electrode surface of the second unit cell comprises a cathode. In some embodiments, a ratio of a height to a width of the welding projection is from about 15% to about 20%. 
     Some embodiments provide a serial cell comprising: a plurality of unit cells; and an inter-connector coupling a lower portion of a first unit cell and an upper portion of a second unit cell. The inter-connector comprises: a supporting frame mechanically coupling the first unit cell and the second unit cell; a welding projection operable to be welded to one of the first unit cell or the second unit cell; and a welding projection surrounding area disposed between the welding projection and the supporting frame. At least a portion of the supporting frame is thicker than the welding projection surrounding area, and at least a portion of the welding projection is thicker than the welding projection surrounding area. 
     In some embodiments, at least a portion of the supporting frame is thicker than an outer wall of a unit cell and a thickness of the welding projection surrounding area equal to or thinner than the outer wall of the unit cell. In some embodiments, a ratio of a height to a width of the welding projection is from about 15% to about 20%. 
     Some embodiments further comprise a spacer dimensioned and configured to prevent short-circuit of the unit cell by the inter-connector. 
     Some embodiments further comprise a first cap assembly disposed on the upper part of the top unit cell; and a second cap assembly placed on the lower part of the bottom unit cell. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages will become apparent and more readily appreciated from the following description of some preferred embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a perspective view of an embodiment of a module cell comprising a plurality of cylindrical unit cells in series; 
         FIG. 2A  is a side view of a cylindrical serial cell comprising an embodiment of inter-connector; 
         FIG. 2B  is an enlarged view of the inter-connector region of the  FIG. 2A ; 
         FIG. 2C  is a cross-sectional view of the region of  FIG. 2B ; 
         FIG. 3  is a perspective view of an embodiment of an inter-connector; 
         FIG. 4A  is a perspective view of an embodiment of a spacer comprising the inter-connector of  FIG. 2B  coupled with a cylindrical unit cell; 
         FIG. 4B  is a perspective view illustrating an inter-connector coupled with the upper part of an spacer, which as shown in  FIG. 4A  is coupled with the upper part of a cylindrical unit cell; 
         FIG. 5A  is a schematic cross-sectional view illustrating a thickness distribution of an embodiment of a fixing wall of the inter-connector of  FIG. 3 ; 
         FIG. 5B  is a schematic cross-sectional view illustrating a thickness distribution of another embodiment of a fixing wall of the inter-connector of  FIG. 3 ; 
         FIG. 6  is a cross-sectional view of an embodiment of the inter-connector of  FIG. 3  combined with the thickness distribution illustrated in  FIG. 5B . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments, wherein a person having ordinary skill in the art can easily carry out the present invention, will be described in a more detailed manner with reference to the accompanying drawings. However, one skilled in the art will understand that changes in many different forms are possible and that the disclosure should not be construed as limited to the embodiments set forth herein. 
     In some embodiments, a serial interface comprises an inter-connector suitable for mechanically fixing and conductably coupling two cylindrical unit cells in series; and optionally, a spacer coupled to the inter-connector, suitable for preventing a short-circuit. Among others, in one aspect, the inter-connector comprises at least one metal material suitable for weldingly fixing the two cylindrical unit cells. In some embodiments of the serial interface not comprising a spacer, the inter-connector forms the serial interface. In some embodiments, an upper part of a top unit cell  40  of a serial cell  30  is a first cap assembly, and the lower part of a bottom unit cell  30  is coupled to a second cap assembly. When a module-type cell  10  comprises a plurality of serial cells  30  in a case, the first and second cap assemblies can function to couple these serial cells  30  to the case. 
       FIG. 2A  shows a side view of a cylindrical serial cell comprising an embodiment of a serial inter-connector.  FIG. 2B  shows a detail view of the serial inter-connector region of the  FIG. 2A .  FIG. 2C  shows a cross-section of the internal structure of the detail illustrated in  FIG. 2B . 
     The serial interface of the cylindrical serial cell shown in  FIGS. 2A and 2B  comprises an inter-connector  200  and a spacer  300  interposed between two cylindrical unit cells  101  and  102 . The inter-connector  200  forms an upper part and the spacer  300  forms a lower part of the serial interface. 
     In the illustrated embodiment, the inter-connector  200  conductively couples an anode outer wall of the first cylindrical unit cell  101  and a cathode terminal of the second cylindrical unit cell  102  to each other. The spacer  300  located between the inter-connector  200  and the anode outer wall of the second cylindrical unit cell  102  is dimensioned and configured to prevent a short-circuit arising from movement of the inter-connector  200 . 
     The outer wall of the spacer  300  can have a larger circumference than the cylindrical unit cells  101  and  102 , which facilitates cooling of the cylindrical unit cells  101  and  102  by forming space between an outer wall of the cylindrical unit cells  101  and  102 , and an inner wall of a module cell frame in which the cylindrical serial cells are disposed. 
       FIG. 3  shows a perspective view of an embodiment of an inter-connector  200 ,  FIG. 4A  shows in perspective an embodiment of a spacer  300  coupled to cylindrical unit cell  102 .  FIG. 4B  shows in perspective an embodiment of an inter-connector  200  coupled with the upper part of the spacer  300 , which, as illustrated in  FIG. 4A , is coupled with the upper part of the cylindrical unit cell  102 . The illustrated embodiment of the spacer  300  insulates a first supporting surface  220  of the inter-connector from the anode outer wall of the second unit cell  102 . 
     The inter-connector  200  shown in  FIG. 3  comprises a generally ring-shaped fixing wall  240  dimensioned and configured to receive therein the anode outer wall of the first cylindrical unit cell  101  and a first welding projection  244  positioned and configured for welding to the first cylindrical unit cell  101 , for example, by contact resistance welding. A first supporting surface  220  extending inwardly from the fixing wall  240  is dimensioned and configured to contact and support the anode of the first cylindrical unit cell  101 . A second supporting surface  210  is dimensioned and configured to contact and support the cathode-end surface of the second cylindrical unit cell  102 . In the illustrated embodiment, the second supporting surface  210  comprises a second welding projection  212  suitable for welding to the second unit cell  102 , for example, by contact resistance welding. A step wall  230  extends between the first supporting surface  220  and the second supporting surface  210 , thereby forming a step between the first supporting surface  220  and the second supporting surface  210  in the illustrated embodiment. 
     The fixing wall  240 , the first supporting surface  220 , the second supporting surface  210 , and the step wall  230  can be formed in an integrated frame. To provide sufficient strength to the serial interface, the at least a portion of the fixing wall  240  and at least a portion of the second supporting surface  210  are preferably thicker than the outer wall of the cylindrical unit cell, for example, from about 0.4 T to about 0.5 T. 
     In some embodiments of the fixing wall  240 , the thickness of the area  241  surrounding welding projection is about equal to or thinner than the anode outer wall of the first cylindrical unit cell  101 , and the first welding projection  244  is thicker than the area  241  surrounding the first welding projection. 
     Optionally, a thickness of an area  211  of the second supporting surface  210  surrounding the second welding projection  212  is equal to or thinner than area of the cathode-end surface of the unit cell  102  to which it is welded. In some embodiments in which the cathode-end surface of the unit cell  102  is sufficiently thick, for example, at least about 0.8 T, the thickness of the area  211  surrounding the welding projection  212  does not adversely affect weldability. In some embodiments in which the cathode-end surface of the unit cell  102  is thinner than the second supporting surface  210  however, the thinner area surrounding the second welding projection  212  provides a better weld. 
       FIG. 5A  is a schematic cross-sectional view of one embodiment of a thickness profile of the fixing wall  240 , and  FIG. 5B  is a schematic cross-sectional view of another embodiment of a thickness profile of the fixing wall  240  of the inter-connector of  FIGS. 3 ,  4 A, and  4 B. 
     In  FIGS. 5A and 5B , the thickness of a portion of the fixing wall  240  is T 1 , the thickness of the welding projection is T 3 , and the thickness of the welding projection surrounding area is T 2 . In the illustrated embodiment, T 1  is thicker than the outer wall of a unit cell to which the welding projection is to be welded, for example, at lest about 0.6 T. 
     In the illustrated embodiments, T 2  of the welding projection surrounding area is about equal to or thinner than the outer wall of the unit cell  101  to which it will be welded. For example, for a unit cell outer wall about 0.4 T thick, T 2  is about 0.4 T or less. For a unit cell outer wall of about 0.5 T, T 2  is about 0.5 T or less. The thinning creates a higher resistance for the area  241  surrounding the welding projection  244  compared with the resistance of outer wall of the unit cell  101 . Consequently, during welding, a considerable amount of current flows from the welding electrode A 2  to the outer wall of the unit cell  101 . As a result, although the thickness of the inter-connector  200  is considerable, it is stably welded to a relatively thin outer wall of the unit cell  101 . In the embodiment illustrated in  FIG. 5A , the thickness T 3  of the welding projection  244  is selected to increase its resistance. Contact between the welding electrode and the welding projection  244  is poor, however, as indicated by the contact portion A 2  of the welding electrode, causing the welding projection  244  to adhere to the welding electrode. Furthermore, a thinner welding projection  244  can contribute less metal to the weld to the outer wall of the unit cell  101 , thereby increasing the likelihood of weld failure. 
     In the embodiment illustrated in  FIG. 5B , the thickness T 3  of the welding projection  244  is a sum of the T 2  (thickness of the welding projection surrounding area) and the (H (height of the welding projection). One result of the illustrated configuration is improved contact between the contacting portion A 2  of the welding electrode and the welding projection  244 , thereby improving weldability and preventing adhesion of the welding electrode. Moreover, the projection  244  provides a sufficient amount of metal to provide a secure weld to the outer wall of the unit cell  101 . 
     In some preferred embodiments, a height-to-width ratio (H/W) of the welding projection  244  is from about 15% to about 20%. At higher H/W ratios, the contact area A 2  between the welding projection and the outer wall of the unit cell  101  is reduced, thereby reducing the current flowing from the welding electrode to the outer wall of the unit cell  101 , which can result in insufficient melting of the welding projection  244 , leading to poor weld strength. At lower H/W ratios, the volume of metal in the welding projection  244  is too large, resulting in poor melting during welding. 
       FIG. 6  is a cross-sectional view of an embodiment of an inter-connector  200  similar to the embodiment illustrated in  FIG. 3  in which both the first  244  and the second  212  welding projections and their surrounding area have the structure of  FIG. 5 . The one-piece frame of the inter-connector  200  comprises a fixing wall  240 , a first supporting surface  220 , a step wall  230 , and a second supporting surface  210 , all of which in the illustrated embodiment have generally uniform thicknesses. 
     The illustrated inter-connector can be welded to an anode outer wall of a cylindrical unit cell  101  inserted into the fixing wall  240  and seated on the first supporting surface  220  by contacting a welding electrode with the first welding projection surrounding area  241  and melting the first welding projection  244  as discussed above. Also as discussed above, in some embodiments in which the cathode outer wall of the cylindrical unit cell  102  is thicker than the frame of the inter-connector  200 , the second welding projection and surrounding area need not have the thickness profiles discuss herein. 
     Embodiments of the serial cell comprising the disclosed inter-connector  200  exhibit improved welds, while assuring sufficient mechanical strength to support the two unit cells. Some embodiments also provide the manufacture of a serial inter-connector with these advantages at low cost. 
     For example, although a generally cylindrical unit cell comprising a cathode is formed as a terminal and an anode formed as an outer wall of the cell is described above, those skilled in the art will understand that the cathode and the anode may be formed in the opposite arrangement or in other shapes. Those skilled in the art will understand that the serial interface is also applicable to such cells. 
     Although some embodiments have been shown and described herein, those skilled in the art will appreciate that changes can be made without departing from the principles and spirit of the disclosure, the scope of which is defined in the appended claims and their equivalents.