Patent Publication Number: US-2013230746-A1

Title: Secondary battery

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0022567, filed on Mar. 5, 2012 in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Aspects of embodiments of the present invention relate to a secondary battery. 
     2. Description of the Related Art 
     A lithium ion battery is a type of secondary battery. In the lithium ion battery, lithium ions move from a negative electrode to a positive electrode during a discharge operation while the lithium ions move from a positive electrode to a negative electrode during a charge operation. The lithium ion battery is widely used in portable electronic devices because it has a high energy density, lacks a memory effect, and is low in natural discharge rate during nonuse. In addition, the lithium ion battery is increasingly used in various application fields, including electronic tools, electric bicycles, electric motorcycles, electric automobiles, airplanes, and so on, due to its high energy density. 
     The lithium ion battery is largely composed of a positive electrode, a negative electrode, and an electrolyte, which are made of a variety of materials. For example, graphite is most widely used as a negative electrode material on a commercial basis. A lamellar-type lithium cobalt oxide or a lithium manganese oxide is generally used as a positive electrode material. The voltage, cycle life, capacity, and stability of a battery may greatly change according to the materials used in the positive and negative electrodes and electrolyte. 
     The capacity of a battery may be indicated in milliampere-hours (mAh) or ampere-hours (Ah). A cellular phone battery capacity is usually in a range of approximately 800 to 1000 mAh, and a smartphone battery capacity is in a range of approximately 1100 to 1950 mAh. A notebook computer battery capacity is in a range of approximately 2400 to 5500 mAh. 
     SUMMARY 
     According to an aspect of embodiments of the present invention, a secondary battery is configured to prevent or substantially prevent leakage of an adhesive when a bottom case is attached to a battery cell using the adhesive. 
     According to an embodiment of the present invention, a secondary battery includes: a battery cell; a protection circuit module electrically connected to the battery cell; a top case covering the protection circuit module; and a bottom case covering a bottom surface of the battery cell, and the bottom case includes one or more trenches formed in a direction away from the bottom surface of the battery cell. 
     The one or more trenches may be formed in a direction away from a periphery of the bottom surface of the battery cell. 
     The secondary battery may further include an adhesive between the periphery of the bottom surface of the battery cell and the one or more trenches of the bottom case. 
     The secondary battery may further include an adhesive between the bottom surface of the battery cell and the bottom case. 
     The secondary battery may further include an adhesive between the bottom surface of the battery cell and the one or more trenches of the bottom case. 
     The bottom case may have a pair of linear long sides spaced apart from each other and a pair of curved short sides connecting opposite ends of the linear long sides, and the one or more trenches may be spaced apart from the pair of linear long sides, respectively. 
     The one or more trenches may be substantially parallel to the pair of linear long sides, respectively. 
     The one or more trenches may be spaced apart from the pair of curved short sides, respectively. 
     The one or more trenches may be substantially parallel to the pair of curved short sides, respectively. 
     The bottom case may have a pair of linear long sides spaced apart from each other and a pair of curved short sides connecting opposite ends of the linear long sides, and the one or more trenches may be formed along inner peripheries of the pair of linear long sides, respectively. The one or more trenches may be formed along inner peripheries of the pair of curved short sides, respectively. 
     In one embodiment, the one or more trenches may be formed in solid line types. In one embodiment, the one or more trenches may be formed in dash line types, 
     The one or more trenches may have a depth of 5% to 50% of a thickness of the bottom case. 
     The bottom case may further include a planar first surface closely contacting the bottom surface of the battery cell and a second surface opposite to the first surface, and each of the one or more trenches may have an inclined surface inclined from the first surface toward the second surface, and a curved surface curved from the inclined surface toward a periphery of the bottom case. 
     The battery cell may include a pair of long side regions, and the bottom case may further include close contact portions extending to the long side regions of the battery cell and closely contacting the long side regions. 
     The secondary battery may further include a label wrapping the battery cell, the top case, and the bottom case. 
     According to another embodiment of the present invention, a secondary battery includes: a battery cell; a case covering a surface of the battery cell; and an adhesive between the case and the surface of the battery cell, and the case includes one or more trenches formed in a direction away from the surface of the battery cell, the one or more trenches receiving the adhesive therein. 
     According to an aspect of embodiments of the present invention, since trenches having a depth (e.g., a predetermined depth) are formed in a bottom case adhered to a battery cell using an adhesive, leakage of the adhesive is prevented or substantially prevented during adhesion between the battery cell and the bottom case. 
     Additional aspects and/or advantages of the present invention are 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 
       The above and other features and aspects of the present invention will become more apparent to those of ordinary skill in the art by describing in detail some exemplary embodiments with reference to the attached drawings, in which: 
         FIGS. 1A and 1B  are a perspective view and an exploded perspective view, respectively, of a secondary battery according to an embodiment of the present invention; 
         FIGS. 2A and 2B  are partial cross-sectional views of the secondary battery of  FIG. 1 , taken along the lines  2   a - 2   a  and  2   b - 2   b,  respectively; 
         FIG. 3  is an enlarged view of a region “3” shown in  FIG. 2B ; 
         FIGS. 4A and 4B  are a perspective view and a partial cross-sectional view, respectively, of a bottom case of a secondary battery according to an embodiment of the present invention; 
         FIG. 5  is a perspective view of a bottom case of a secondary battery according to another embodiment of the present invention; 
         FIG. 6  is a perspective view of a bottom case of a secondary battery according to another embodiment of the present invention; 
         FIGS. 7A to 7D  are partial cross-sectional views of bottom cases of a secondary battery including various types of trenches according to other embodiments of the present invention; and 
         FIGS. 8A and 8B  illustrate states in which a battery cell of a secondary battery is being adhered to a bottom case using an adhesive, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Some exemplary embodiments of the present invention are described more fully hereinafter with reference to the accompanying drawings; however, embodiments of the present invention may be embodied in different forms and should not be construed as limited to the exemplary embodiments illustrated and set forth herein. Rather, these exemplary embodiments are provided by way of example for understanding of the invention and to convey the scope of the invention to those skilled in the art. As those skilled in the art would realize, the described embodiments may be modified in various ways, all without departing from the spirit or scope of the present invention. 
       FIGS. 1A and 1B  are a perspective view and an exploded perspective view, respectively, of a secondary battery  100  according to an embodiment of the present invention. 
     As shown in  FIGS. 1A and 1B , the secondary battery  100  according to an embodiment of the present invention includes a battery cell  110 , a protection circuit module  120 , a top case  130 , a bottom case  140 , and a label  160 . 
     The battery cell  110  charges or discharges electric energy and, in one embodiment, has a bottom surface  111 , a pair of long side regions  112  upwardly extending from the bottom surface  111 , a pair of short side regions  113  connecting the pair of long side regions  112  in a curved shape, a cap plate  114  covering the pair of long side regions  112  and the pair of short side regions  113 , and a terminal  115  formed in the cap plate  114 . In one embodiment, the bottom surface  111 , the pair of long side regions  112 , and the pair of short side regions  113  are collectively referred to as a can or a case. The can may be formed of aluminum, an aluminum alloy, steel, nickel-plated steel, or any other suitable material. In one embodiment, the cap plate  114  may be welded to the can, such as via laser welding, and may be formed of aluminum, an aluminum alloy, steel, nickel-plated steel, or any other suitable material. The terminal  115 , in one embodiment, is electrically insulated from the cap plate  114 . 
     An electrode assembly (not shown) including a positive electrode plate, a separator, a negative electrode plate, and an organic electrolyte (not shown) are accommodated in the battery cell  110 . The battery cell  110  may be a lithium ion battery or a lithium polymer battery. However, embodiments of the present invention are not limited thereto. Since a configuration of the battery cell  110  is well known in the art, a detailed description thereof will be omitted. 
     The protection circuit module  120  prevents or substantially prevents overcharge, overdischarge, or overcurrent of the battery cell  110 . The protection circuit module  120 , in one embodiment, includes a printed circuit board  121 , a plurality of electronic protection devices  122  mounted on the printed circuit board  121 , cell terminals  123   a  and  123   b  formed on a surface of the printed circuit board  121 , and a pack terminal  124  formed on another surface of the printed circuit board  121 . One cell terminal  123   a  may be electrically connected to the cap plate  114  of the battery cell  110  through a connection plate  125 , and the other cell terminal  123   b  may be electrically connected to the terminal  115  of the battery cell  110  through a thermally-sensitive safety device  126 . In one embodiment, the thermally-sensitive safety device  126  may be a positive temperature coefficient (PTC) device having resistance values increasing according to a temperature increase. 
     The top case  130  covers the protection circuit module  120 , thereby protecting the protection circuit module  120  against external surroundings. That is, the top case  130  prevents or substantially prevents external foreign matter from penetrating into the protection circuit module  120  and may prevent or substantially prevent the protection circuit module  120  from being damaged due to a falling shock of the secondary battery  100 . The top case  130  includes one or more openings  131  to allow the pack terminal  124  of the protection circuit module  120  to be exposed to the outside. The top case  130  may be preformed using a plastic resin to then be coupled to the protection circuit module  120 . Alternatively, the top case  130  may be manufactured by mounting the battery cell  110  and the protection circuit module  120  in a mold to then be injection molded. 
     The bottom case  140  covers the bottom surface  111  of the battery cell  110 , thereby protecting the battery cell  110  from being damaged due to a falling shock of the secondary battery  100 . The bottom case  140  may be preformed using a plastic resin to then be coupled to the bottom surface  111  of the battery cell  110 . 
     The bottom case  140 , in one embodiment, has a pair of linear long sides  141  spaced apart from each other, and a pair of curved short sides  142  connecting opposite ends of the pair of linear long sides  141 . The pair of linear long sides  141  of the bottom case  140  correspond to the pair of long side regions  112  of the battery cell  110 , and the pair of curved short sides  142  of the bottom case  140  correspond to the pair of short side regions  113  of the battery cell  110 . In one embodiment, regions (e.g., predetermined regions) of the bottom case  140  consisting of the pair of linear long sides  141  and the pair of curved short sides  142  may cover the bottom surface  111  of the battery cell  110 . 
     The bottom case  140  covers the bottom surface  111  of the battery cell  110  and includes one or more trenches  143  formed in a direction away from the bottom surface  111  of the battery cell  110 . Here, the expression “away from the bottom surface  111  of the battery cell  110 ” means that the trenches  143  become deeper as they become farther away from the bottom surface  111  of the battery cell  110 . 
     In one embodiment, the bottom case  140  further includes close contact portions  144  extending by a length (e.g., a predetermined length) toward the long side regions  112  of the battery cell  110  to closely contact the long side regions  112  of the battery cell  110 . 
     In one embodiment, an adhesive  150  is disposed between the bottom case  140  and the bottom surface  111  of the battery cell  110 , and the bottom case  140  and the battery cell  110  may not be separated from each other. 
     In one embodiment, the label  160  covers the battery cell  110 , the top case  130 , and the bottom case  140 . In one embodiment, a top region of the top case  130  and a bottom region of the bottom case  140  are exposed to the outside through the label  160 , and the label  160  covers the pair of long side regions  112  and the pair of short side regions  113  of the battery cell  110 , thereby protecting the battery cell  110  against external surroundings and preventing or substantially preventing the battery cell  110  from being unnecessarily electrically short circuited. 
       FIGS. 2A and 2B  are partial cross-sectional views of the secondary battery of  FIG. 1 , taken along the lines  2   a - 2   a  and  2   b - 2   b,  respectively. 
     As shown in  FIGS. 2A and 2B , in one embodiment, the protection circuit module  120  is electrically connected to the battery cell  110  on the battery cell  110  through the connection plate  125  and the thermally-sensitive safety device  126  and is covered by the top case  130 . The pack terminal  124  of the protection circuit module  120  is exposed to the outside through the openings  131  formed in the top case  130 . 
     The bottom case  140  is mechanically coupled to a lower portion of the battery cell  110 , and the adhesive  150  is disposed between the battery cell  110  and the bottom case  140 . Since the trenches  143  are formed in the bottom case  140 , the adhesive  150  is prevented or substantially prevented from being exposed to the outside when the battery cell  110  and the bottom case  140  are adhered to each other using the adhesive  150 . 
     In one embodiment, since the battery cell  110 , the close contact portions  144  of the bottom case  140 , and the top case  130  are wrapped by the label  160 , the top case  130  and the bottom case  140  may not be separated from the battery cell  110 . The top region of the top case  130  is exposed to the outside through the label  160  and the bottom region of the bottom case  140  is exposed to the outside through the label  160 . 
       FIG. 3  is an enlarged view of a region “3” shown in  FIG. 2B . 
     As shown in  FIG. 3 , the bottom case  140  has a generally planar first surface  145  closely contacting the bottom surface  111  of the battery cell  110 , and a second surface  146  opposite to the first surface  145 . In one embodiment, each of the trenches  143  has an inclined surface  143   a  inclined from the first surface  145  toward the second surface  146 , and a curved surface  143   b  curved from the inclined surface  143   a  toward a periphery of the bottom case  140 . In such a manner, the trenches  143  may be formed in a direction away from the periphery of the bottom surface  111  of the battery cell  110 . 
     The adhesive  150  may be disposed between the bottom surface  111  of the battery cell  110  and the first surface  145  of the bottom case  140 . However, during adhesion between the battery cell  110  and the bottom case  140 , the adhesive  150  in a liquid phase may flow to the trenches  143  each having the inclined surface  143   a  and the curved surface  143   b.  Since the trenches  143  are formed to have a depth (e.g., a predetermined depth), the adhesive  150  may not flow to the outside of the trenches  143 . That is, the adhesive  150  may not leak out from the secondary battery  100 . In one embodiment, the adhesive  150  stays between the periphery of the bottom surface  111  of the battery cell  110  and the trenches  143  of the bottom case  140 . 
     According to an embodiment of the present invention as described above, an undesirable outer appearance due to leakage of the adhesive  150  and failure due to impurity generation may be prevented or substantially prevented. 
     In an exemplary embodiment, the trenches  143  are formed to have a depth of approximately 5% to 50% of a thickness of the bottom case  140 . 
     Here, the thickness of the bottom case  140  refers to a thickness from the first surface  145  to the second surface  146 . The bottom case  140  has a thickness great enough to prevent or substantially prevent the battery cell  110  from being damaged due to a falling shock of the secondary battery  100 . Therefore, the bottom case  140  may have a thickness varying according to a size, shape, and weight of the battery cell  110 . 
     Therefore, even if the trenches  143  have different depths according to the thickness of the bottom case  140 , the depths of the trenches  143 , in an exemplary embodiment, are approximately 5% to 50% of the thickness of the bottom case  140 . 
     If each of the trenches  143  has a depth of less than approximately 5% of the thickness of the bottom case  140 , the excessively shallow trenches  143  may cause the adhesive  150  to be leaked. If each of the trenches  143  has a depth of greater than approximately 50% of the thickness of the bottom case  140 , too great an amount of the adhesive  150  may flow into the trenches  143 , thereby lowering adhesion efficiency between the battery cell  110  and the bottom case  140 . 
       FIGS. 4A and 4B  are a perspective view and a partial cross-sectional view, respectively, of a bottom case  140  of the secondary battery  100 , according to an embodiment of the present invention. 
     As shown in  FIGS. 4A and 4B , the bottom case  140  has the pair of linear long sides  141  spaced apart from each other and the pair of curved short sides  142  connecting the pair of linear long sides  141 . The close contact portions  144  may be formed in the pair of linear long sides  141 . 
     In one embodiment, the trenches  143  may be formed to be spaced apart from the pair of linear long sides  141  and may be formed to be parallel or substantially parallel to the pair of linear long sides  141 . In addition, the trenches  143  may be formed to be spaced apart from the pair of curved short sides  142  and may be formed to be parallel or substantially parallel to the pair of curved short sides  142 . 
     In one embodiment, the trenches  143  may be formed along inner regions of the pair of linear long sides  141  and may be formed to be parallel or substantially parallel to the pair of linear long sides  141 . In addition, the trenches  143  may be formed along inner regions of the pair of curved short sides  142  and may be formed to be parallel or substantially parallel to the pair of curved short sides  142 . 
     In one embodiment, the trenches  143  may be formed on the first surface  145  of the bottom case  140  in a substantially closed curve. Therefore, during adhesion between the battery cell  110  and the bottom case  140  using the adhesive  150 , the adhesive  150  may not leak through any region of the bottom case  140 . 
       FIG. 5  is a perspective view of a bottom case  240  of a secondary battery according to another embodiment of the present invention. 
     As shown in  FIG. 5 , trenches  243  of the bottom case  240  may be formed to be spaced apart from the pair of linear long sides  141  or along inner regions of the pair of linear long sides  141 . That is, the trenches  243 , in one embodiment, are not formed in the pair of curved short sides  142 . The trenches  243 , in one embodiment, may be generally formed in solid line types parallel or substantially parallel to the pair of linear long sides  141  of the bottom case  240 . 
     In the bottom case  240 , a reduction in strength may not occur in the pair of curved short sides  142 . For example, if the secondary battery falls, the severest shock may be applied to corner regions of the secondary battery. Therefore, if the secondary battery falls, the corner regions of the secondary battery may be damaged. However, as described above, since the trenches  243  causing a reduction in mechanical strength are not formed in the pair of curved short sides  142  of the bottom case  240  corresponding to the corner regions of the secondary battery, the secondary battery may have an increased strength to withstand the falling shock. 
     In one embodiment, during adhesion between the battery cell  110  and the bottom case  240 , an amount of the adhesive  150  may be somewhat accurately controlled so that even when the trenches  243  are formed only at the pair of linear long sides  141  of the bottom case  240 , the adhesive  150  may not be exposed to the outside through the pair of curved short sides  142 . That is, the trenches  243  formed only at the pair of linear long sides  141  of the bottom case  240  may hold all of the adhesive  150  therein so as not to leak out. 
       FIG. 6  is a perspective view of a bottom case  340  of a secondary battery according to another embodiment of the present invention. 
     In one embodiment, as shown in  FIG. 6 , trenches  343  are formed at the pair of linear long sides  141  of the bottom case  340 . The trenches  343  may be generally formed in dash line types. The trenches  343 , in one embodiment, are not formed at the pair of curved short sides  142  of the bottom case  340 , and are formed to be parallel to the pair of linear long sides  141  of the bottom case  340 . As such, the bottom case  340  may not have a reduced mechanical strength of the pair of curved short sides  142  while minimizing or reducing a reduction in mechanical strength of the pair of linear long sides  141 . Therefore, a secondary battery including the bottom case  340  may have an increased strength to withstand a falling shock. 
     In other embodiments, such as where an amount of the adhesive  150  is more accurately controlled during adhesion between the battery cell  110  and the bottom case  340 , the trenches  343  may be formed not only in dash line types but in dot line types, dash-dot line types, or dash-dot-dot line types. 
       FIGS. 7A to 7D  are partial cross-sectional views of bottom cases of a secondary battery including various types of trenches according to other embodiments of the present invention. 
     According to another embodiment of the present invention, as shown in  FIG. 7A , a trench  443  of a bottom case  440  has a side surface  443   a  formed vertically or substantially vertically from the first surface  145  toward the second surface  146 , and a bottom surface  443   b  connected to the side surface  443   a  and formed horizontally or substantially horizontally, or parallel, to the first surface  145  and the second surface  146 . That is, the trench  443  has a substantially rectangular cross-sectional shape. As such, the trench  443  has a relatively large volume, thereby holding a relatively large amount of the adhesive  150 . 
     According to another embodiment of the present invention, as shown in  FIG. 7B , a trench  543  of a bottom case  540  has an inclined surface  543   a  substantially inclined from the first surface  145  toward the second surface  146 , such that the trench  543  has a substantially triangular cross-sectional shape. As such, the trench  543  has a relatively small volume, thereby reducing a reduction in mechanical strength of the bottom case  540 . 
     According to another embodiment of the present invention, as shown in  FIG. 7C , a trench  643  of a bottom case  640  has an inclined surface  643   a  substantially inclined from the first surface  145  toward the second surface  146 , and a bottom surface  643   b  connected to the inclined surface  643   a  and formed horizontally or substantially horizontally, or parallel, to the first surface  145  and the second surface  146 . In one embodiment, the trench  643  has a larger entrance width than a width of the bottom surface  643   b.  That is, the trench  643  has a substantially inversely trapezoidal cross-sectional shape. As such, the trench  643  is relatively easily taken out from a mold, thereby facilitating injection molding of the bottom case  640 . 
     According to another embodiment of the present invention, as shown in  FIG. 7D , a trench  743  of a bottom case  740  has an inclined surface  743   a  substantially inclined from the first surface  145  toward the second surface  146 , and a bottom surface  743   b  connected to the inclined surface  743   a  and formed horizontally or substantially horizontally, or parallel, to the first surface  145  and the second surface  146 . In one embodiment, the trench  743  has a smaller entrance width than a width of the bottom surface  743   b.  That is, the trench  743  has a substantially trapezoidal cross-sectional shape. As such, a coupling force between the adhesive  150  filling the trench  743  and the bottom case  740  may be relatively increased. Therefore, separation of a battery cell and the bottom case  740  may be more effectively prevented or reduced. 
       FIGS. 8A and 8B  illustrate states in which the battery cell  110  of the secondary battery  100  is being adhered to the bottom case  140  using the adhesive  150 , according to an embodiment of the present invention. 
     In one embodiment, as shown in  FIG. 8A , a uniform or substantially uniform amount of the adhesive  150  is applied to the bottom surface  111  of the battery cell  110 . Conversely, a uniform or substantially uniform amount of the adhesive  150  may be applied to the bottom case  140 . 
     Next, as shown in  FIG. 8B , the battery cell  110  and the bottom case  140  are coupled to each other. If the amount of the adhesive  150  is greater than a reference amount, the adhesive  150  may be disposed between the battery cell  110  and the first surface  145  of the bottom case  140 . In addition, since the adhesive  150  may flow to the trenches  143  of the bottom case  140 , it may be between the battery cell  110  and the trenches  143  of the bottom case  140 . However, the trenches  143  hold the adhesive  150  and prevent or substantially prevent the adhesive  150  from leaking out from the battery cell  110  and the bottom case  140 . 
     Although some exemplary embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.