Abstract:
A secondary battery including: an electrode assembly; a case receiving the electrode assembly and including a plurality of stepped sections at an inner side of the case in contact with the electrode assembly; and at least one electrode tab electrically connected with the electrode assembly and withdrawn toward an outside of the case. In the secondary battery, a friction force between the inner side of the case and the electrode assembly is increased due to the plurality of stepped sections, thereby minimizing or reducing movement of the electrode assembly within the case.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0011169, filed on Feb. 3, 2012 in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Aspects of embodiments of the present invention relate to a secondary battery. 
         [0004]    2. Description of the Related Art 
         [0005]    A secondary battery has a function of charging and discharging. Recently, secondary batteries have been widely used as an energy source in devices such as a smartphone, a notebook computer, and an electric tool, for example. 
         [0006]    Generally, the secondary battery consists of an electrode assembly and a case for receiving the electrode assembly. The electrode assembly consists of an anode plate having a surface of an anode collector coated with an anode active material, a cathode plate having a surface of a cathode collector coated with a cathode active material, and a separator disposed between the anode plate and the cathode plate to electrically isolate the anode plate and the cathode plate, wherein the anode plate, the cathode plate, and the separator may be wound in a jelly roll shape. In addition, the case receives the electrode assembly and covers the electrode assembly. 
         [0007]    In this case, two electrode tabs are exposed to the outside of the case and have one-to-one correspondence with the anode plate and the cathode plate to electrically connect each other. 
         [0008]    When the electrode assembly moves within the case, a deviation of a length of the electrode tabs exposed to the outside may become large and decrease the production yield of the secondary battery. 
       SUMMARY 
       [0009]    According to an aspect of embodiments of the present invention, an electrode assembly and a secondary battery including a case receiving the electrode assembly are capable of improving a production yield by minimizing or reducing a movement of the electrode assembly within the case in the secondary battery. 
         [0010]    According to one embodiment of the present invention, a secondary battery includes: an electrode assembly; a case receiving the electrode assembly and including a plurality of stepped sections at an inner side of the case in contact with the electrode assembly; and at least one electrode tab electrically connected with the electrode assembly and withdrawn toward an outside of the case. 
         [0011]    The case may include at least two stacked layers. In one embodiment, the at least two stacked layers include: a first layer at the inner side of the case, the first layer contacting the electrode assembly in a receiving space of the case and including the stepped sections; and a second layer stacked with the first layer. The second layer may have a hardness greater than a hardness of the first layer. The first layer may include cast polypropylene (CPP). 
         [0012]    The case may further include a third layer stacked with the second layer. The second layer may include a metal, and the third layer may include an insulating material. 
         [0013]    In one embodiment, the plurality of stepped sections includes a plurality of holes formed in the first layer. The second layer may be exposed through the holes. 
         [0014]    The plurality of stepped sections may include a plurality of grooves formed in the first layer and having a depth less than a thickness of the first layer. 
         [0015]    The plurality of stepped sections may include a plurality of protrusions protruding from the first layer. 
         [0016]    In one embodiment, the case includes a receiving section receiving the electrode assembly, and a cover section covering the electrode assembly, the receiving section includes a bottom section, a side wall section extending from the bottom section, and a junction section extending from an upper end section of the side wall section, and the junction section and the cover section are coupled to each other. 
         [0017]    In one embodiment, the plurality of stepped sections are arranged on substantially the entire bottom section. In one embodiment, the plurality of stepped sections are arranged along a periphery of the bottom section. In one embodiment, the plurality of stepped sections are arranged on opposite end sections of the bottom section. 
         [0018]    The case may be a pouch-type case. 
         [0019]    According to an aspect of embodiments of the present invention, a plurality of stepped portions for increasing a friction force between the electrode assembly and the case is formed at a bottom portion of the case in contact with the electrode assembly, wherein movement of the electrode assembly within the case may be minimized or reduced by the stepped portion. 
         [0020]    According to another aspect of embodiments of the present invention, a secondary battery is configured to maintain a length of electrode tabs withdrawn outside of a case constant or substantially constant, thereby improving a production yield of the secondary battery. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The accompanying drawings, together with the specification, illustrate some exemplary embodiments of the present invention, and, together with the description, serve to explain principles and aspects of the present invention. 
           [0022]      FIG. 1  is an exploded perspective view of a secondary battery according to an embodiment of the present invention. 
           [0023]      FIG. 2  is a bottom perspective view of the secondary battery shown in  FIG. 1 . 
           [0024]      FIG. 3  is a cross-sectional view of the secondary battery of  FIG. 1 , taken along the line I-I′. 
           [0025]      FIG. 4A  is an enlarged cross-sectional view of a portion of a secondary battery corresponding to a junction area shown in  FIG. 3 . 
           [0026]      FIG. 4B  is an enlarged cross-sectional view of a portion of a secondary battery corresponding to a receiving area shown in  FIG. 3 . 
           [0027]      FIG. 5  is a cross-sectional view of a secondary battery according to another embodiment of the present invention. 
           [0028]      FIG. 6  is a cross-sectional view of a secondary battery according to another embodiment of the present invention. 
           [0029]      FIG. 7  is a bottom perspective view of a secondary battery according to another embodiment of the present invention. 
           [0030]      FIG. 8  is a bottom perspective view of a secondary battery according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    In the following detailed description, certain exemplary embodiments of the present invention are shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. In addition, when an element is referred to as being “on” another element, it can be directly on the another element or indirectly on the another element with one or more intervening elements interposed therebetween. Also, when an element is referred to as being “connected to” another element, it can be directly connected to the another element or indirectly connected to the another element with one or more intervening elements connected therebetween. Like reference numerals are used herein to refer to like elements. 
         [0032]    Configurations and operations of some exemplary embodiments of the present invention are described herein with reference to the accompanying drawings. 
         [0033]      FIG. 1  is an exploded perspective view of a secondary battery according to an embodiment of the present invention;  FIG. 2  is a bottom perspective view of the secondary battery shown in  FIG. 1 ; and  FIG. 3  is a cross-sectional view of the secondary battery of  FIG. 1 , taken along the line of  FIG. 1 . 
         [0034]    Referring to  FIGS. 1 through 3 , a secondary battery  200  includes an electrode assembly  10  and a case  180  covering, or receiving, the electrode assembly  10 . 
         [0035]    In one embodiment, the electrode assembly  10  includes an anode plate having a surface of an anode collector coated with an anode active material, a cathode plate having a surface of a cathode collector coated with a cathode active material, and a separator disposed between the anode plate and the cathode plate to electrically isolate the anode plate and the cathode plate. In one embodiment, the anode plate, the cathode plate, and the separator are wound in a jelly roll shape. 
         [0036]    Although not shown in detail in the drawings, a first electrode tab  20  is electrically connected to the anode plate to be withdrawn toward the outside of the case  180 , and a second electrode tab  30  is electrically connected to the cathode plate to be withdrawn toward the outside of the case  180 . In the secondary battery  200  according to one embodiment, the first electrode tab  20  and the second electrode tab  30  may be electrically connected to a power terminal of an electrical apparatus, and the secondary battery  200  provides power to the external electrical apparatus. 
         [0037]    In one embodiment, the separator of the electrode assembly is porous and may be made of a film, a non-woven fabric, or the like, and may be made of polyethylene, polypropylene, polyvinylidene fluoride, for example, and interposed between the anode plate and the cathode plate to pass ions between the anode plate and the cathode plate while preventing or substantially preventing direct contact between the anode plate and the cathode plate. 
         [0038]    The case  180 , in one embodiment, includes a receiving section  110  and a cover section  160  having a junction area SA and a receiving area PA. 
         [0039]    The receiving section  110 , in one embodiment, includes a bottom section  130 , a side wall section  140  extending from the bottom section  130 , and a junction section  150  bent from an upper end section of the side wall section  140  to be approximately parallel with the bottom section  130 . In one embodiment of the present invention, the junction section  150  may be formed in a shape surrounding the bottom section  130  having a generally rectangular shape. 
         [0040]    In a construction of the case  180 , the electrode assembly  10  is received within a receiving space  130   a  in the receiving area PA, and the cover section  160  is joined to the junction section  150  in the junction area SA. Therefore, the electrode assembly  10  is covered or contained from the outside of the case  180 . 
         [0041]    According to an embodiment of the present invention, the case  180  is made of a plurality of stacked layers or films different from each other, and a plurality of holes  170  having a stepped shape may be formed in an uppermost layer of the films in contact, or adjacent, with the receiving space  130   a  in the plurality of films corresponding to the bottom section  130 . 
         [0042]    The plurality of holes  170  increases a friction force between the electrode assembly  10  and the bottom section  130  and, accordingly, the friction force of the plurality of the holes  170  minimizes or reduces movement of the electrode assembly  10  within the receiving section  110 . Therefore, this prevents or substantially prevents the first and second electrode tabs  20  and  30  from increasing a deviation of length withdrawn toward the outside of the case  180  according to the movement of the electrode assembly  10 . 
         [0043]    The plurality of films stacked with each other of the case  180  and a structure of the plurality of holes  170  are described in further detail below. 
         [0044]      FIG. 4A  is an enlarged cross-sectional view of a portion of the secondary battery  200  corresponding to the junction area SA shown in  FIG. 3 .  FIG. 4B  is an enlarged cross-sectional view of a portion of the secondary battery  200  corresponding to the receiving area PA shown in  FIG. 3 . 
         [0045]    Referring to  FIG. 4A , in one embodiment, in construction of the case  180  corresponding to the junction area SA, each of the junction section  150  and the cover section  160  includes a first layer L 1 , a second layer L 2 , and a third layer L 3 . 
         [0046]    In one embodiment, in each of the junction section  150  and the cover section  160 , the first layer L 1  and the third layer L 3  are disposed on opposite outermost sides, and the second layer L 2  is stacked between the first layer L 1  and the third layer L 3 . 
         [0047]    According to one embodiment, in a construction of the case  180 , the first layer L 1  of the junction section  150  and the first layer L 1  of the cover section  160  may be joined by a joining process using heat and pressure. 
         [0048]    In one embodiment, the first layer L 1  may be made of cast polypropylene (CPP), and a junction between the junction section  150  and the cover section  160  may be easily made using the joining process. 
         [0049]    The second layer L 2  of the case  180 , in one embodiment, functions to reinforce a strength of the case  180 . Therefore, in one embodiment of the present invention, the second layer L 2  is made of a metal (e.g., aluminum) having a hardness greater than that of the first layer L 1 , and the second layer L 2  may be formed having a thickness greater than that of the first layer L 1  and the third layer L 3 . 
         [0050]    The third layer L 3  of the case  180  covers the second layer L 2  in order to prevent or substantially prevent the second layer L 2  from being exposed to the outside. In one embodiment, when the second layer L 2  is made of a metal, the third layer L 3  may be made of a resin, such as nylon, polypropylene, or polyethylene, for example. 
         [0051]    In one embodiment of the present invention, the third layer L 3  may be formed as single layer, but in other embodiments of the present invention, the third layer L 3  may be formed as a plurality of stacked layers having a different insulating material. 
         [0052]    Referring to  FIGS. 2 and 4B , in one embodiment, in a construction of the case  180  corresponding to the receiving area SA, each of the bottom section  130  and the cover section  160  includes the first layer L 1 , the second layer L 2 , and the third layer L 3 . 
         [0053]    The first layer L 1  of the bottom section  130  is formed with a plurality of stepped portions and, in one embodiment of the present invention, as shown in  FIG. 4B , the plurality of stepped sections is implemented as the plurality of holes  170 . In one embodiment, the plurality of holes  170  is formed over the entire bottom section  130 . Each of the plurality of holes  170 , in one embodiment, is formed by partially removing the first layer L 1  by a thickness (e.g., a predetermined thickness) of the layer. In one embodiment, the second layer L 2  is exposed through the plurality of holes  170 . 
         [0054]    By contrast, in a secondary battery in which a plurality of holes is not formed on a bottom section, a surface of the bottom section is flat, an electrode assembly disposed on the bottom section moves within the bottom section, and a deviation of a length of first and second electrode tabs withdrawn toward the outside can increase. However, according to embodiments of the present invention, the bottom section  130  has a stepped section in a position of the plurality of holes  170  to increase a friction force between the bottom section  130  and the electrode assembly  10 , such that movement of the electrode assembly  10  on the bottom section  130  is minimized or reduced. Therefore, the deviation of the length of the first and second electrode tabs  20  and  30  exposed to the outside is minimized or reduced to improve a production yield. 
         [0055]      FIG. 5  is a cross-sectional view of a secondary battery according to another embodiment of the present invention. A location of the cross-section of the secondary battery shown in  FIG. 5  corresponds to that of the cross-section of the secondary battery  200  shown in  FIG. 4B . 
         [0056]    Comparing the secondary battery  200  described above and shown in  FIG. 4B  with a secondary battery  201  according to another embodiment of the present invention, as shown in  FIG. 5 , it is noted that the construction in the bottom section  130  of the secondary battery  200  and a bottom section  131  of a case  181  of the secondary battery  201  is different and that the other components and features are the same. Therefore, further description of the components and features of the secondary battery  201  that are the same as those described above with respect to the secondary battery  200  will not be repeated. 
         [0057]    The bottom section  131  of the case  181 , in one embodiment, includes a first layer L 11 , the second layer L 2 , and the third layer L 3  that are stacked (e.g., sequentially stacked), and the first layer L 11  is formed with a plurality of stepped sections. In one embodiment, as shown in  FIG. 5 , the plurality of stepped sections is formed as a plurality of grooves  171 . The grooves  171 , in one embodiment, are formed to have a depth less than a thickness of the first layer L 11 . The plurality of grooves  171 , in one embodiment, may be formed over the entire bottom section  131 . 
         [0058]    Like the effect produced by the plurality of holes  170  in the secondary battery  200  described above with respect to  FIG. 4B , the bottom section  131  has a stepped shape in the plurality of grooves  171  to increase a friction force between the bottom section  131  and the electrode assembly  10 , such that movement of the electrode assembly  10  on the bottom section  131  is minimized or reduced. 
         [0059]      FIG. 6  is a cross-sectional view of a secondary battery according to another embodiment of the present invention. A location of the cross-section of the secondary battery shown in  FIG. 6  corresponds to that of the cross-section of the secondary battery  200  shown in  FIG. 4B . 
         [0060]    Comparing the secondary battery  200  described above and shown in  FIG. 4B  with a secondary battery  202  according to another embodiment of the present invention, as shown in  FIG. 6 , it is noted that the construction in the bottom section  130  of the secondary battery  200  and a bottom section  132  of a case  182  of the secondary battery  202  is different and that the other components and features are the same. Therefore, further description of the components and features of the secondary battery  202  that are the same as those described above with respect to the secondary battery  200  will not be repeated. 
         [0061]    The bottom section  132  of the case  182 , in one embodiment, includes a first layer L 12 , the second layer L 2 , and the third layer L 3  that are stacked (e.g., sequentially stacked), and the first layer L 12  is formed with a plurality of stepped sections. In one embodiment, as shown in  FIG. 6 , the plurality of stepped sections is formed as a plurality of protrusions  173  protruding from the first layer L 12 . The plurality of protrusions  173 , in one embodiment, may be formed over the entire bottom section  132 . 
         [0062]    Like the effect produced by the plurality of holes  170  in the secondary battery  200  described above with respect to  FIG. 4B , the bottom section  132  has a stepped shape in the plurality of protrusions  173  to increase a friction force between the bottom section  132  and the electrode assembly  10 , such that movement of the electrode assembly  10  on the bottom section  132  is minimized or reduced. 
         [0063]      FIG. 7  is a bottom perspective view of a secondary battery according to another embodiment of the present invention. Comparing the secondary battery  200  described above and shown in  FIG. 2  with a secondary battery  203  according to another embodiment of the present invention, as shown in  FIG. 7 , it is noted that a position of a plurality of holes  170  in a bottom section  133  of a case  183  of the secondary battery  203  is different than that of the secondary battery  200  and that the other components and features are the same. 
         [0064]    Therefore, further description of the components and features of the secondary battery  203  that are the same as those described above with respect to the secondary battery  200  will not be repeated. 
         [0065]    Referring to  FIG. 7 , in one embodiment, the bottom section  133  of the case  183  is formed with the plurality of holes  170 , and the plurality of holes  170  is formed at both of opposite end sections of the bottom section  133 . Therefore, the friction force between both end sections of the bottom section  133  and the electrode assembly  10  placed on both end sections is increased by the plurality of holes  170 , and movement of the electrode assembly  10  on the bottom section  133  is minimized or reduced in a similar effect as described above with reference to  FIGS. 1 through 4B . 
         [0066]    In the secondary battery  203  according to one embodiment, as shown in  FIG. 7 , the plurality of holes  170  is formed on the bottom section  133 . However, in another embodiment, the plurality of grooves  171  described above with reference to  FIG. 5  or the plurality of protrusions  173  described above with reference to  FIG. 6  may be formed on the bottom section  133  instead of or in combination with the holes  170 . 
         [0067]      FIG. 8  is a bottom perspective view of a secondary battery according to another embodiment of the present invention. Comparing the secondary battery  200  described above and shown in  FIG. 2  with a secondary battery  204  according to another embodiment of the present invention, as shown in  FIG. 8 , it is noted that a position of a plurality of holes  170  in a bottom section  134  of a case  184  of the secondary battery  204  is different than that of the secondary battery  200  and that the other components and features are the same. 
         [0068]    Therefore, further description of the components and features of the secondary battery  204  that are the same as those described above with respect to the secondary battery  200  will not be repeated. 
         [0069]    Referring to  FIG. 8 , in one embodiment, the bottom section  134  of the case  184  is formed with the plurality of holes  170 , and the plurality of holes  170  is formed along a border section, or periphery section, surrounding a center section of the bottom section  134 . Therefore, the friction force between the border section of the bottom section  134  and the electrode assembly  10  placed on the border section is increased by the plurality of holes  170 , and movement of the electrode assembly  10  on the bottom section  134  is minimized or reduced in a similar effect as described above with reference to  FIGS. 1 through 4B . 
         [0070]    In the secondary battery  204  according to one embodiment, as shown in  FIG. 8 , the plurality of holes  170  is formed on the bottom section  134 . However, in another embodiment, the plurality of grooves  171  described above with reference to  FIG. 5  or the plurality of protrusions  173  described above with reference to  FIG. 6  may be formed on the bottom section  134  instead of or in combination with the holes  170 . 
         [0071]    While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.