Patent Publication Number: US-2011052974-A1

Title: Secondary battery

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2009-0082371, filed Sep. 2, 2009 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Aspects of the present invention relate to a secondary battery, and more particularly, to a secondary battery that prevents movement of an electrode assembly housed in a can, thereby increasing stability. 
     2. Description of the Related Technology 
     Secondary batteries are rechargeable and thus repeatedly used. Therefore, secondary batteries are widely used as energy sources for electronic devices in various fields. While the secondary batteries have been generally used in compact electronic devices (such as MP3 players, cameras, and portable multimedia players (PMPs)) due to their small capacity, as high-capacity and high-output batteries are developed, the secondary batteries are also being applied to hybrid cars, handheld electronic/electrical appliances and so forth on a commercial level. 
     Among these secondary batteries, a lithium secondary battery is widely used due to a high operating voltage and a high energy density per unit weight. The lithium secondary battery is formed by housing an electrode assembly and an electrolyte in an outer case, and sealing the outer case. The lithium secondary battery may be classified as a can type or a pouch type depending on the shape of the outer case. Furthermore, the can type may be classified as a cylindrical shape or a prismatic shape. The cylindrical secondary battery is formed by housing an electrode assembly and an electrolyte in a can, and inserting an insulating gasket and a cap assembly into an opening of the can to seal the can. 
     Generally, the cylindrical secondary battery is formed by inserting the insulating gasket into the opening of the can, inserting components of the cap assembly into the insulating gasket, and crimping a side of the can and the insulating gasket to seal the can. When the electrode assembly is housed in the can, a predetermined space needs to be ensured between an outer surface of the electrode assembly and an inner surface of the can to prevent damage to the electrode assembly due to contact with the can. 
     As described above, since the electrode assembly is housed in the can but not fixed to the can, if the space between the inner surface of the can and the outer surface of the electrode assembly is large, the electrode assembly may be easily moved as a result of an external impact. Due to the movement of the electrode assembly, an attached electrode tab may be detached, or a crack may be generated in the electrode tab. Thus, it is difficult to ensure stability. 
     SUMMARY 
     Aspects of the present invention provide a secondary battery that has a recessed portion formed on a side surface of a can to optimize a gap between an inner surface of the can and an outer surface of an electrode assembly, and thus an electrode plate has no defect, and movement of the electrode assembly is effectively prevented, thereby increasing stability. 
     According to an aspect of the present invention, there is provided a secondary battery having an electrode assembly and a can housing the electrode assembly, wherein the can includes at least one recessed portion in a side surface thereof, and a value obtained by subtracting a diameter of the electrode assembly from a gap length between facing inner surfaces of the can ranges from about −0.12 mm to about 0.10 mm. 
     According to another aspect of the present invention, there is provided a secondary battery including an electrode assembly and a can housing the electrode assembly, wherein the can includes at least one recessed portion in a side surface thereof, and a sum of a gap length between an inner surface of the can where a recessed portion, of the at least one recessed portion, is disposed and an outer surface of the electrode assembly and a gap length between the inner surface of the can facing the recessed portion and the outer surface of the electrode assembly ranges from about −0.12 mm to about 0.10 mm. 
     According to an aspect of the present invention, the at least one recessed portion includes a pair of recessed portions which face each other, and a value obtained by subtracting the diameter of the electrode assembly from the gap between the inner surfaces of the facing recessed portions may range from about −0.12 mm to about 0.10 mm. 
     According to an aspect of the present invention, when only one recessed portion is formed, the sum of the gap length between the inner surface of the can in which the recessed portion is disposed and the outer surface of the electrode assembly and the gap length between the inner surface of the can in which the recessed portion is not disposed and the outer surface of the electrode assembly may range from about −0.12 mm to about 0.10 mm. 
     According to an aspect of the present invention, the at least one recessed portion may be formed along a lengthwise or circumferential direction of the can. 
     According to an aspect of the present invention, the at least one recessed portion may be formed to correspond to a side surface of the electrode assembly. 
     According to an aspect of the present invention, the at least one recessed portion may be formed to correspond to an upper, middle and/or lower portions of the electrode assembly. 
     According to an aspect of the present invention, the at least one recessed portion may have a polygonal or semi-circular cross-section. 
     According to another aspect of the present invention, there is provided a can to house an electrode assembly of a secondary battery, the can including: a bottom surface; a side surface extending from the bottom surface to form a housing for the electrode assembly; at least one protruding portion extending from the side surface into the housing, wherein a value obtained by subtracting a diameter of an area to house the electrode assembly from a gap length between the at least one protruding portion and a facing inner surface of the can ranges from −0.696864% to 0.5858% of the diameter of the area to house the electrode assembly. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is an exploded perspective view of a secondary battery according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view briefly illustrating a part of the secondary battery according to an embodiment of the present invention; 
         FIG. 3  is a plan view of the cross-sectional view of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view briefly illustrating a part of a secondary battery according to another embodiment of the present invention; and 
         FIGS. 5A to 5F  are plan and cross-sectional views of various recessed portions according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. Moreover, in the drawings, the length and thickness of an element or a region may be exaggerated for clarity. Furthermore, a part being “connected” with another part means that the parts are “directly connected” or “electrically connected” with each other, possibly having a third device therebetween. 
       FIG. 1  is an exploded perspective view of a secondary battery  1  according to an embodiment of the present invention,  FIG. 2  is a cross-sectional view briefly illustrating a part of the secondary battery  1  according to an embodiment of the present invention,  FIG. 3  is a plan view of the cross-sectional view of  FIG. 2 ,  FIG. 4  is a cross-sectional view briefly illustrating a part of the secondary battery  1  according to another embodiment of the present invention, and  FIGS. 5A to 5F  are plan and cross-sectional views of various recessed portions according to embodiments of the present invention. 
     Referring to  FIG. 1 , the secondary battery  1  includes an electrode assembly  10 , a can  20  housing the electrode assembly  10 , and a recessed portion  30  formed by partially recessing a side surface of the can  20 . The recessed portion  30  will be described in further detail with reference to  FIGS. 2 through 5F . However, it is understood that, in the present description, the recessed portion  30  is recessed from an interior of the can  20  such that the recessed portion  30  protrudes towards an inside of the can  20 . The electrode assembly  10  includes a first electrode plate  11 , a second electrode plate  13 , and a separator. The first and second electrode plates  11  and  13  have different polarities from each other. The separator  15  is disposed between the first and second electrode plates  11  and  13  to prevent a short circuit between the first and second electrode plates  11  and  13 . 
     While not limited thereto, the electrode assembly  10  may be formed in a jelly roll shape, i.e, by stacking and winding the first electrode plate  11 , the second electrode plate  13  and the separator  15 . Thus, the electrode assembly  10  is formed in a circular shape, and has a hollow center  12  in a middle thereof. Here, a component disposed at an outermost portion of the electrode assembly  10  formed in a jelly-roll shape may, although not necessarily, be a finishing tape attached to an outer surface of the electrode assembly  10  to prevent unwinding of an outer end of the electrode assembly  10 . 
     The first and second electrode plates  11  and  13  are each formed by applying a positive or negative electrode active material slurry to a collector plate made of aluminum or copper. For example, a positive electrode plate is formed by applying the positive electrode active material slurry to the collector plate made of aluminum, and a negative electrode plate is formed by applying the negative electrode active material slurry to the collector plate made of copper. The first and second electrode plates  11  and  13  include non-coating portions, respectively, through which the collector plate is exposed since no active material slurry is applied thereon. First and second electrode tabs  17  and  19  are electrically connected to the non-coating portions, respectively. To be specific, the first electrode tab  17  is connected to the non-coating portion formed on the first electrode plate  11 , and the second electrode tab  19  is connected to the non-coating portion formed on the second electrode plate  13 . As illustrated in  FIG. 1 , the first electrode tab  17  is led upward from the electrode assembly  10  to an opening of the can  20 , and the second electrode tab  19  is led downward from the electrode assembly  10  to a bottom of the can  20 . However, it is understood that aspects of the present invention are not limited thereto. For example, the second electrode tab  19  may be led upward and the first electrode tab  17  downward. Alternatively, the first and second electrode tabs  17  and  19  may be led in the same direction as each other 
     The can  20  may be formed of a metal such as aluminum or stainless steel, and formed in a cylindrical shape having an opening at one end to house the electrode assembly  10 . The electrode assembly  10  is inserted into the can  20  through the opening. 
     Although not shown in the drawings, the secondary battery  1  may include a cap assembly to seal the can  20 . Between the opening of the can  20  and the cap assembly, an insulating gasket may be interposed to prevent a short circuit between the can  20  and the cap assembly. The cap assembly is coupled to the opening of the can  20  to seal the can  20 , and blocks electrical flow when an internal pressure of the can  20  increases more than a predetermined level, thereby increasing stability of the secondary battery  1 . In addition, the secondary battery  1  may include insulating plates disposed on and/or under the electrode assembly  10  to prevent a short circuit between the electrode assembly  10  and the can  20  and lessen an external impact, and a center pin disposed in the hollow center  20  of the electrode assembly  10  to prevent deformation of the electrode assembly  10  and exhaust an internal gas generated from the electrode assembly  10 . 
     Referring to  FIGS. 2 and 3 , the secondary battery  1  includes a recessed portion  30  formed in the can  20 . For convenience of description, the present embodiment illustrates four recessed portions  30 , which are separately formed in pairs to face each other, and the electrode assembly  10 , which is disposed in the middle of the can  20 . However, aspects of the present invention are not limited thereto, as more or less than four recessed portions  30  may be provided and/or the recessed portions  30  may not be provided in pairs. The recessed portion  30  may be formed by partially recessing a side surface of the can  20  by pressing, so that no additional material is needed. 
     As shown in  FIGS. 2 and 3 , L 1  is a length of a gap between inner surfaces  31  of the recessed portions  30  facing each other, L 2  is a diameter of the electrode assembly  10 , and L 3  and L 4  are respective lengths of gaps between inner surfaces  31  of the recessed portions  30  and outer surfaces  101  of the electrode assembly  10 . A value (L 1 −L 2 ) is obtained by subtracting the diameter L 2  of the electrode assembly from the length of the gap L 1  between the inner surfaces  31  of the facing recessed portions  30 . The (L 1 −L 2 ) value for the shown example is maintained in the range from about −0.12 mm to about 0.10 mm. In the present embodiment, the electrode assembly  10  is disposed in the middle of the can  20 , and thus both lengths L 3  and L 4  between the inner surfaces  31  of the recessed portions  30  and the outer surfaces  101  of the electrode assembly  10  are equal to (L 1 −L 2 )/2 (i.e., the lengths L 3  and L 4  are equal to each other). However, it is understood that the (L 1 −L 2 ) value can be other values, depending on the size of the battery. 
     As a result, in the cross-sectional view, the sum of both lengths L 3  and L 4  between the inner surfaces  31  of the recessed portions  30  formed in the can  20  and the outer surfaces  101  of the electrode assembly  10  respectively range from about −0.12 mm to about 0.10 mm. Here, the symbol “−” denotes the state in which the recessed portion  30  presses the electrode assembly  10  to be recessed inwardly. Thus, L 2  is determined from an uncompressed state, such as prior to assembly or in an area of the electrode assembly  10 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Gap length between 
                   
               
               
                   
                 inner surfaces of 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 recessed portion 
                 Diameter of J/R 
                 L1 − L2 
                 Drum Test (Defect of electrode tab) 
                 Defect of 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 (L1, mm) 
                 (L2, mm) 
                 (mm) 
                 100 min. 
                 130 min. 
                 150 min. 
                 electrode plate 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 C. example 1 
                 17.30 
                 17.05 
                 0.25 
                 yes 
                 yes 
                 yes 
                 none 
               
               
                 C. example 2 
                 17.27 
                 17.08 
                 0.19 
                 none 
                 yes 
                 yes 
                 none 
               
               
                 C. example 3 
                 17.20 
                 17.08 
                 0.12 
                 none 
                 none 
                 yes 
                 none 
               
               
                 E. example 1 
                 17.17 
                 17.07 
                 0.10 
                 none 
                 none 
                 none 
                 none 
               
               
                 E. example 2 
                 17.33 
                 17.23 
                 0.10 
                 none 
                 none 
                 none 
                 none 
               
               
                 E. example 3 
                 17.31 
                 17.22 
                 0.09 
                 none 
                 none 
                 none 
                 none 
               
               
                 E. example 4 
                 17.36 
                 17.30 
                 0.06 
                 none 
                 none 
                 none 
                 none 
               
               
                 E. example 5 
                 17.06 
                 17.01 
                 0.05 
                 none 
                 none 
                 none 
                 none 
               
               
                 E. example 6 
                 17.17 
                 17.13 
                 0.04 
                 none 
                 none 
                 none 
                 none 
               
               
                 E. example 7 
                 17.26 
                 17.23 
                 0.03 
                 none 
                 none 
                 none 
                 none 
               
               
                 E. example 8 
                 17.24 
                 17.22 
                 0.02 
                 none 
                 none 
                 none 
                 none 
               
               
                 E. example 9 
                 17.10 
                 17.22 
                 −0.12 
                 none 
                 none 
                 none 
                 none 
               
               
                 C. example 4 
                 17.01 
                 17.18 
                 −0.17 
                 none 
                 none 
                 none 
                 yes 
               
               
                 C. example 5 
                 17.00 
                 17.20 
                 −0.20 
                 none 
                 none 
                 none 
                 yes 
               
               
                   
               
            
           
         
       
     
     Table 1, above, shows whether a defect is generated in the electrode tab  17  and/or  19  and the electrode plates  11  and/or  13  after a drum test is carried out while changing the length of the gap L 1  between the inner surfaces  31  of the facing recessed portions  30  and the diameter L 2  of the electrode assembly  10 . As shown in Table 1, in the experimental examples (E. example)  1  through  9 , no defect was generated in either the electrode tab  17  and/or  19  or the electrode plate  11  and/or  13 . However, in the comparative examples (C. example)  1  through  3 , no defect was generated in the electrode plate  11  and/or  13 , but a defect was generated in the electrode tab  17  and/or  19 . Thus, as the gap length L 3  and L 4  between the inner surface of the can  20  and the outer surface  101  of the electrode assembly  10  increases, a defect is more easily generated in the electrode tab  17  and/or  19  because the electrode assembly  10  is more easily moved. 
     In the comparative examples 4 and 5, no defect was generated in the electrode tab  17  and/or  19 , but a defect was generated in the electrode plate  11  and/or  13 . Thus, when the electrode assembly  10  is recessed so deeply, movement of the electrode assembly  10  can be prevented, but the electrode plate  11  and/or  13  can be damaged. Therefore, when the gap length L 3  and/or L 4  between the inner surface of the can  20  and the outer surface  101  of the electrode assembly  30  is relatively large, the electrode assembly  30  can be easily moved, and thus the electrode tab  17  and/or  19  may have a defect such as a crack or a short circuit at a contact portion. However, when the outer surface  101  of the electrode assembly  10  is recessed so deeply to prevent the movement of the electrode assembly  10 , the electrode plate  11  and/or  13  can be damaged. As a result, when the sum of both the gap lengths L 3  and L 4  between the inner surface of the can  20  in which the recessed portions  30  are formed and the outer surface  101  of the electrode assembly  10  ranges from about −0.12 mm to about 0.10 mm, the movement of the electrode assembly  10  can be effectively prevented without the generation of defects in the electrode plates  11  and  13 . Alternatively, it can be seen from Table 1 that when the sum of both the gap lengths L 3  and L 4  ranges from −0.696864% to 0.5858% of the diameter L 2  of the electrode assembly, the movement of the electrode assembly  10  can be effectively prevented without the generation of defects in the electrode plates  11  and  13 . Similarly, when the (L 1 −L 2 ) value ranges from −0.696864% to 0.5858% of the diameter L 2  of the electrode assembly, the movement of the electrode assembly  10  can be effectively prevented without the generation of defects in the electrode plates  11  and  13 . 
     In the present embodiment, a central axis of the electrode assembly  10  is disposed in the middle of the can  20 . However, it is understood that aspects of the present invention are not limited thereto. That is, the central axis of the electrode assembly  10  may be disposed apart from the middle of the can  20 , and/or the recessed portions  30  may not face each other. For example, referring to  FIG. 4 , in the cross-sectional view, the central axis of the electrode assembly  10  is not disposed in the middle of the can  20 , and one recessed portion  30  is formed without facing a corresponding recessed portion. In this case, the gap L 3  between the inner surface  31  of the recessed portion  30  and the outer surface  101  of the electrode assembly  10  and the gap L 4  between an inner surface  22  of the can  20  in which the recessed portion  30  is not formed and the outer surface  101  of the electrode assembly  10  may differ from each other, but the sum (L 3 +L 4 ) of the gap length L 3  between the inner surface  31  of the recessed portion  30  and the outer surface  101  of the electrode assembly  10  and the gap length L 4  between the inner surface  22  of the can  20  and the outer surface  101  of the electrode assembly  10  ranges from about −0.12 mm to about 0.10 mm according to aspects of the present invention. 
     As described above, aspects of the present invention do not necessarily have the recessed portions  30  facing each other, but the recessed portions  30  may be disposed to face each other or not to face each other. In the cross-sectional view, when the recessed portions  30  face each other, the sum of the gap lengths (L 3  and L 4  in  FIG. 3 ) between the inner surfaces of the can  20  (i.e., the inner surface  31  of the recessed portion  30 ) in which the recessed portions  30  are disposed and the outer surface  101  of the electrode assembly  10  is maintained in the range from about −0.12 mm to about 0.10 mm. Similarly, when the recessed portions  30  do not face each other, the sum of the gap length (L 3  in  FIG. 4 ) between the inner surface of the can  20  in which the recessed portions  30  are disposed (i.e., the inner surface  31  of the recessed portion  31 ) and the outer surface  101  of the electrode assembly  10  and the gap length (L 4  in  FIG. 4 ) between the inner surface  22  of the can  20  in which the recessed portions  30  are not disposed and the outer surface  101  of the electrode assembly  10  is maintained in the range from about −0.12 mm to about 0.10 mm. 
       FIGS. 5A to 5F  are plan and cross-sectional views of various recessed portions according to embodiments of the present invention. At least one recessed portion  30  may be formed along a lengthwise direction of the can  20 , as shown in  FIGS. 2 through 4 , to prevent the movement of the electrode assembly  10 . Furthermore, the at least one recessed portion  30  may have a polygonal cross-section. However, it is understood that aspects are not limited thereto. For example, as an alternative, at least one recessed portion  30  may be formed along a circumferential direction of the can  20 , as shown in  FIG. 5A , and/or may have a semi-circular cross-section as shown in  FIG. 5B . As shown in  FIG. 5C , the recessed portion  30  may be formed to the same length as the electrode assembly  10  to correspond to a side surface of the electrode assembly  10 , or may be formed longer than the electrode assembly  10 . As shown in  FIGS. 5D to 5F , the recessed portion  30  may be formed to correspond to upper, middle or lower portions of the electrode assembly  10 , or may be formed to correspond to at least two different portions. That is, the recessed portion  30  may be formed to correspond to at least one of upper, middle and lower portions of the electrode assembly  10 . 
     According to aspects of the present invention, no defect is generated in an electrode plate  11  and  13  through use of one or more recesses, and movement of an electrode assembly  10  is effectively prevented, thereby increasing stability. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.