Abstract:
A secondary battery comprises an electrode assembly comprising a first electrode plate, a second electrode plate and a separator interposed between the first and second electrode plates; and a battery case accommodating the electrode assembly, the battery case comprising a first portion, a second portion, and an adhesive layer that contacts a surface of the first portion and a surface of the second portion, wherein the adhesive layer is continuous between the first and second portions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Application No. 61/312,125, filed on Mar. 9, 2010, the entire content of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    Aspects of the present invention relate to a secondary battery. 
         [0004]    2. Description of the Related Technology 
         [0005]    A lithium secondary battery or rechargeable battery can be manufactured in a bare cell, and the bare cell may include an electrode assembly having a positive electrode plate, a negative electrode plate, and a separator, and a case for receiving the electrode assembly. 
         [0006]    In general, a case for a bare cell is typically formed of an aluminum can or a composite aluminum pouch. 
         [0007]    When the case is formed of an aluminum can, it is typically heavy while having a high strength. By contrast, when the case is formed of a composite aluminum pouch, it is typically poor in strength while being lightweight. 
         [0008]    Accordingly, research is being conducted in secondary batteries having a case that is rigid and lightweight. 
       SUMMARY 
       [0009]    Aspects of the present invention provide a secondary battery with increased resistance against external impacts, lightness and enhanced sealing efficiency. 
         [0010]    According to aspects of the present invention, a secondary battery includes an electrode assembly having electrode tabs connected thereto, a hard case including a first hard case and a second hard case, and a thermal adhesion layer disposed at a contacting area of the first hard case and the second hard case. 
         [0011]    According to aspects of the present invention, the thermal adhesion layer may be bonded by thermal bonding. In addition, the thermal adhesion layer may be a film-like layer. The thermal adhesion layer may include any one selected from modified polyolefine based materials and acid-modified polyolefine based materials. The thermal adhesion layer may be made of a material that is bonded by heat of approximately 130° C. or higher. 
         [0012]    According to aspects of the present invention, the hard case may have a higher melting point than the thermal adhesion layer. 
         [0013]    The hard case may be formed of at least one selected from the group consisting of polyolefine-based resin, epoxy resin, polycarbonate resin, polyethyleneterephthalate resin, polyetheretherketone resin, high-density polyethylene resin, and acryl-based resin. 
         [0014]    In addition, the hard case may have a Rockwell hardness of not less than 55 R scales. 
         [0015]    According to aspects of the present invention, each of the first hard case and the second hard case may be formed in a box shape. Here, each of the first hard case and the second hard case may have a thickness of approximately 0.5 mm or greater. 
         [0016]    According to aspects of the present invention, the first hard case may be formed in a box shape and the second hard case may be formed in a plate shape. 
         [0017]    According to aspects of the present invention, the first hard case may further include a first metal layer formed on the outer surface thereof, and the second hard case may further include a second metal layer formed on the outer surface thereof. 
         [0018]    Here, each of the first metal layer and the second metal layer may be made of at least one selected from the group consisting of aluminum (Al), nickel (Ni), iron (Fe), and copper (Cu). 
         [0019]    According to aspects of the present invention, the first hard case may further include a first metal layer formed therein, and the second hard case may further include a second metal layer formed therein. 
         [0020]    According to aspects of the present invention, the first hard case may further include a first metal layer formed on the inner surface thereof, and the second hard case may further include a second metal layer formed on the inner surface thereof. 
         [0021]    According to aspects of the present invention, the first hard case may further include a first thermal conduction layer formed therein, and the second hard case may further include a second thermal conduction formed therein. 
         [0022]    Here, each of the first thermal conduction layer and the second thermal conduction layer may be formed by impregnating ceramic powder into polymer fiber or non-woven fabric. 
         [0023]    According to aspects of the present invention, each of the first hard case and the second hard case may be foamed in a box shape. The first hard case may have an accommodating portion for accommodating ends of the second hard case at contacting areas S thereof where the first hard case and second hard case are coupled to each other. Here, each of the first and second hard cases may have a thickness of 0.3 mm or greater. In addition, a thermal adhesion layer may be disposed within the accommodating portion. 
         [0024]    In the secondary battery according to an exemplary embodiment, a hard case surrounding an electrode assembly is formed using a plastic resin that is lightweight and resistant against external impacts, thereby increasing the resistance against external impacts and realizing lightness in a simplified manner. 
         [0025]    In addition, since the secondary battery includes a hard case constituted by a first hard case and a second hard case, which are coupled to each other by thermal bonding using a thermal adhesion layer, the sealing efficiency of the hard case can be enhanced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The aspects, features and advantages of embodiments of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
           [0027]      FIG. 1  is an assembled perspective view of a secondary battery according to an embodiment of the present invention; 
           [0028]      FIG. 2  is a disassembled perspective view of the secondary battery shown in  FIG. 1 ; 
           [0029]      FIG. 3  is a sectional view taken along line A-A′ of  FIG. 1 ; 
           [0030]      FIG. 4  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to another embodiment of the present invention; 
           [0031]      FIG. 5  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention; 
           [0032]      FIG. 6  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention; 
           [0033]      FIG. 7  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention; 
           [0034]      FIG. 8  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention; 
           [0035]      FIG. 9  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention; and 
           [0036]      FIG. 10  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention. 
           [0037]      FIG. 11  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention. 
           [0038]      FIG. 12  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Embodiments of the present invention will now be described in detail with reference to the accompanying figures. 
         [0040]      FIG. 1  is an assembled perspective view of a secondary battery according to an embodiment of the present invention,  FIG. 2  is a disassembled perspective view of the secondary battery shown in  FIG. 1 , and  FIG. 3  is a sectional view taken along line A-A′ of  FIG. 1 . 
         [0041]    Referring to  FIGS. 1 and 2 , the secondary battery  100  according to an embodiment of the present invention includes an electrode assembly  10 , a hard case (or a battery case)  20  and a thermal adhesion layer (or an adhesive layer)  50 . The secondary battery  100  may be electrically connected to an external electric device (not shown) to perform a charging operation to be supplied with power or a discharging operation to supply power. 
         [0042]    The electrode assembly  10  may be formed by winding or stacking a laminate of a first electrode plate  11 , a separator  13 , and a second electrode plate  12 , which are formed as a thin plate or layer. In addition, the electrode assembly  10  can include electrode tabs, that is, a first electrode tab  15  and a second electrode tab  16 . Here, the outer surface of the electrode assembly  10  may have a rounded profile. 
         [0043]    According to an embodiment, the first electrode plate  11  can include a first electrode collector formed of aluminum foil, and a first electrode active material coated on the first electrode collector. Lithium cobalt oxide (LiCoO 2 ) may be used as the first electrode active material. 
         [0044]    According to an embodiment, the second electrode plate  12  can include a second electrode collector formed of a copper foil, and a second electrode active material coated on the second electrode collector. Carbon may be used as the second electrode active material. 
         [0045]    The first electrode plate  11  may operate as a positive electrode and the second electrode plate  12  may operate as a negative electrode. The first electrode plate  11  and the second electrode plate  12  may have different polarities. 
         [0046]    The separator  13  may be made of polyethylene, polypropylene, or a copolymer of polyethylene and polypropylene. The separator  13  may be formed to have a width greater than the first electrode plate  11  or the second electrode plate  12 , which is advantageous for preventing an electrical short-circuit between the electrode plates  11  and  12 . 
         [0047]    The first electrode tab  15  and the second electrode tab  16  extending from the first electrode plate  11  and the second electrode plate  12  may electrically connect the electrode assembly  10  to an external device (not shown). Insulating tapes  17  for preventing short-circuits between the first electrode tab  15  and the second electrode tab  16  may be disposed on boundary portions of the first electrode tab  15  and the second electrode tab  16 , which extend through a lower case  20 . 
         [0048]    The hard case  20  may accommodate the electrode assembly  10  and an electrolyte (not shown), and may include a first hard case (or a first portion)  30  and a second hard case (or a second portion)  40 . The hard case  20  may surround the electrode assembly  10  to protect the same from the outside. Here, the electrolyte is impregnated into the electrode assembly  10  and may be disposed between the hard case  20  and electrode assembly  10 . 
         [0049]    The first hard case  30  may be shaped of a box having one surface opened to accommodate the electrode assembly  10 . In detail, the first hard case  30  can include a first bottom surface (or a first main surface)  31 , a first lateral surface (or first lateral edge)  32  bent and extending from an end of the first bottom surface  31 , and first grooves  33  formed at portions of the first lateral surface  32  to allow the first electrode tab  15  and the second electrode tab  16  to pass. Here, a first lead-out surface LS 1  of the first lateral surface  32 , from which the first electrode tab  15  and the second electrode tab  16  are drawn out, a first opposite surface LS 2  facing and opposite to the first lead-out surface LS 1 , and first connection surfaces LS 3  and LS 4  connected to the first lead-out surface LS 1  and the first opposite surface LS 2 , may be at right angle with respect to the first bottom surface  31 , respectively, to facilitate a formation process of the first hard case  30 . 
         [0050]    In addition, the first hard case  30  may include an electrolyte injection hole  35  through which the electrolyte (not shown) is injected into the hard case  20 . The electrolyte injection hole  35  may be sealed by a plug  36 . The electrolyte injection hole  35  may be formed in the second hard case  40 , and the formation location of the electrolyte injection hole  35  is not limited to the illustrated example. Meanwhile, a space within the first hard case  30  that accommodates a portion of the electrode assembly  10  is referred to herein as a first space  30   a.    
         [0051]    Like the first hard case  30 , the second hard case  40  may be shaped of a box having one surface opened to accommodate the electrode assembly  10 . In detail, the second hard case  40  may include a second bottom surface (or a second main surface)  41 , a second lateral surface (or a second lateral edge)  42  bent and extending from an end of the second bottom surface  41 , and second grooves  43  formed at portions of the second lateral surface  42  to allow the first electrode tab  15  and the second electrode tab  16  to pass. Here, a second lead-out surface SS 1  of the second lateral surface  42 , from which the first electrode tab  15  and the second electrode tab  16  are drawn out, a second opposite surface SS 2  facing and opposite to the second lead-out surface SS 1 , and second connection surfaces SS 3  and SS 4  connected to the second lead-out surface SS 1  and the second opposite surface SS 2 , may be at right angle with respect to the second bottom surface  41 , respectively, to facilitate a formation process of the second hard case  40 . 
         [0052]    Meanwhile, a space within the second hard case  40  that accommodates the remaining portion of the electrode assembly  10  is referred to herein as a second space  40   a.    
         [0053]    In order to increase the resistance of the hard case  20  against external impacts, the first hard case  30  and the second hard case  40  may be formed of a plastic resin that is resistant against external impacts and lightweight, that is, at least one selected from the group consisting of polyolefine-based resin, epoxy resin, polycarbonate resin, polyethyleneterephthalate resin, polyetheretherketone resin, high-density polyethylene resin, and acryl-based resin. Examples of the polyolefine-based resin may include polypropylene resin and polyethylene resin. Examples of the acryl-based resin may include polymethlymethacrylate resin. Here, materials for forming the first hard case  30  and the second hard case  40  may have a Rockwell hardness of not less than 55 R scales to have a scratch-proof property, which, can improve the external appearance of the hard case  20 . In addition, internal surfaces of the first hard case  30  and the second hard case  40  may be constructed so as to not react with the electrolyte, or be subjected to surface treatment. Further, each of the first hard case  30  and the second hard case  40  may have a thickness of approximately 0.5 mm or greater to maintain the mechanical strength against external impacts after they are coupled to each other. Here, upper limits to the thicknesses of the first hard case  30  and the second hard case  40  are not defined because the respective thicknesses of the first hard case  30  and the second hard case  40  may vary according to materials forming the same and to the use of the secondary battery. 
         [0054]    The first hard case  30  and the second hard case  40  may be formed by separately performing injection molding, respectively. 
         [0055]    The thermal adhesion layer  50 , as illustrated in  FIG. 3 , may be disposed at a contacting area S of the first hard case  30  and the second hard case  40 . In detail, the thermal adhesion layer  50  may be disposed between an end  32   a  of the first lateral surface  32  and an end  42   a  of the second lateral surface  42  in a continuous manner, or such that no other element exists between the end  32   a  of the first lateral surface  32  and the end  42   a  of the second lateral surface  42 . The thermal adhesion layer  50  may be a casted polypropylene film-like layer, which is disposed at the end  32   a  of the first lateral surface  32  or the end  42   a  of the second lateral surface  42 , and may couple the first hard case  30  and the second hard case  40  to each other by thermal bonding. Since the thermal adhesion layer  50  may be subjected to thermal bonding in a state in which it is disposed between the end  32   a  of the first lateral surface  32  and the end  42   a  of the second lateral surface  42  in a continuous manner, the sealing efficiency of the first hard case  30  and the second hard case  40  can be enhanced. Here, the thermal adhesion layer  50  may be made of a material that is bonded by heat of approximately 130° C. or higher, and examples thereof may include any one material selected from modified polyolefine-based materials and acid-modified polyolefine-based materials. Examples of the modified polyolefine-based materials may include modified polypropylene, and examples of the acid-modified polyolefine-based materials may include acid-modified polypropylene. 
         [0056]    Meanwhile, materials for forming the first hard case  30  and the second hard case  40  may have a higher melting point than for forming the thermal adhesion layer  50 . If the materials for forming the first hard case  30  and the second hard case  40  have a lower melting point than for forming the thermal adhesion layer  50 , the first hard case  30  and the second hard case  40  may be melted by heat for bonding the thermal adhesion layer  50 . 
         [0057]    As described above, in the secondary battery  100  according to an embodiment of the present invention, the hard case  20  surrounding the electrode assembly  10  may be formed using a plastic resin that is lightweight and resistant against external impacts. Thus, a secondary battery may be formed with increased resistance against external impacts and lightness in a simplified manner, compared to the conventional battery in which an electrode assembly is surrounded by an aluminum can or wrapped by a pouch formed of an aluminum composite material, which can involve complex manufacturing processes. 
         [0058]    In addition, since the secondary battery  100  may include the hard case  20  constituted by the first hard case  30  and the second hard case  40 , which may be coupled to each other by thermal bonding using the thermal adhesion layer  50 , the sealing efficiency of the hard case  20  can be enhanced, compared to the conventional secondary battery in which cases are coupled to each other by ultrasonic welding. 
         [0059]    A secondary battery according to another embodiment of the present invention will now be described. 
         [0060]      FIG. 4  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to another embodiment of the present invention. 
         [0061]    The secondary battery according to the embodiment of  FIG. 4  is substantially the same as the secondary battery  100  shown in  FIG. 2  in view of configuration and functions, except for the configurations of a hard case  120  and a thermal adhesion layer  150 . Thus, repetitive explanations will be omitted and the following description will be focused on the hard case  120  and the thermal adhesion layer  150 . 
         [0062]    Referring to  FIG. 4 , the hard case  120  can include a first hard case  130  and a second hard case  140 . The hard case  120  can be substantially the same as the hard case  20  shown in  FIG. 3 , except that the first hard case  130  of the hard case  120  can further include a first metal layer  134  formed on the outer surface thereof, and the second hard case  140  can further include a second metal layer  144  formed on the outer surface thereof. 
         [0063]    Each of the first metal layer  134  and the second metal layer  144  may be made of a metallic material, and examples thereof may include any one selected from aluminum (Al), nickel (Ni), iron (Fe) and copper (Cu). The first metal layer  134  and the second metal layer  144  can effectively prevent external moisture from being infiltrated into the hard case  120 . In addition, the first metal layer  134  and the second metal layer  144  can prevent the electrolyte accommodated in the hard case  120  from leaking outside. Further, the first metal layer  134  and the second metal layer  144  can further enhance the strength of the hard case  120  against external impacts. 
         [0064]    The thermal adhesion layer  150  may be substantially the same as the thermal adhesion layer  50  shown in  FIG. 3 , except that the thermal adhesion layer  150  may be larger than the thermal adhesion layer  50  shown in  FIG. 3  so as to couple the first hard case  130  including the first metal layer  134  and the second hard case  140  including the second metal layer  144  to each other. 
         [0065]    As described above, in the secondary battery according to another embodiment of the present invention, the first metal layer  134  and the second metal layer  144  may be further formed on outer surfaces of the first hard case  130  and the second hard case  140 , respectively, thereby effectively preventing internal components from corroding due to infiltration of moisture. In addition, malfunctions in charging and discharging operations due to electrolyte leakage can be effectively prevented. Moreover, the electrode assembly  10  can be protected from external impacts more efficiently. 
         [0066]    A secondary battery according to still another embodiment of the present invention will now be described. 
         [0067]      FIG. 5  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention. 
         [0068]    The secondary battery according to the current embodiment may be substantially the same as the secondary battery  100  shown in  FIG. 2  in view of configuration and functions, except for the configurations of a hard case  220  and a thermal adhesion layer  250 . Thus, repetitive explanations will be omitted and the following description will be focused on the hard case  220  and the thermal adhesion layer  250 . 
         [0069]    Referring to  FIG. 5 , the hard case  220  can include a first hard case  230  and a second hard case  240 . The hard case  220  may be substantially the same as the hard case  120  shown in  FIG. 4 , except that the first hard case  230  of the hard case  220  can further include a first metal layer  234  formed therein, and the second hard case  240  can further include a second metal layer  244  formed therein. 
         [0070]    The first metal layer  234  and the second metal layer  244  can enhance the efficiency of coupling the first hard case  230  and the second hard case  240  to each other. In addition, the first metal layer  234  and the second metal layer  244  can prevent external moisture from being infiltrated into the hard case  220  or the electrolyte accommodated in the hard case  220  from leaking outside. Moreover, the first metal layer  234  and the second metal layer  244  can further enhance the strength of the hard case  220  against external impacts. In the embodiment shown in  FIG. 5 , the first metal layer  234  is thinner than a portion of the first hard case  230 , the portion excluding the first metal layer  234  from the first hard case  230 , and the second metal layer  244  is thinner than a portion of the second hard case  240 , the portion excluding the second metal layer  244  from the second hard case  240 . In alternative embodiments, however, in order to further enhance the strength of the hard case  220  against external impacts, the first metal layer  234  may be formed to be thicker than a portion of the first hard case  230 , the portion excluding the first metal layer  234  from the first hard case  230 , and the second metal layer  244  may be formed to be thicker than a portion of the second hard case  240 , the portion excluding the second metal layer  244  from the second hard case  240 . 
         [0071]    The thermal adhesion layer  250  may be substantially the same as the thermal adhesion layer  50  shown in  FIG. 3 , except that the thermal adhesion layer  250  may be larger than the thermal adhesion layer  50  shown in  FIG. 3  so as to couple the first hard case  230  including the first metal layer  234  and the second hard case  240  including the second metal layer  244  to each other. 
         [0072]    As described above, in the secondary battery according to still another embodiment of the present invention, the first metal layer  234  and the second metal layer  244  may be further formed in the first hard case  230  and the second hard case  240 , respectively, thereby allowing the first metal layer  234  and the second metal layer  244  to be coupled to the first hard case  230  and the second hard case  240 , respectively, in a more secured manner. In addition, it is possible to effectively prevent internal components from corroding due to infiltration of moisture. In addition, malfunctions in charging and discharging operations due to electrolyte leakage can be effectively prevented. Moreover, the electrode assembly  10  can be protected from external impacts more efficiently. 
         [0073]    A secondary battery according to still another embodiment of the present invention will now be described. 
         [0074]      FIG. 6  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention. 
         [0075]    The secondary battery according to the current embodiment may be substantially the same as the secondary battery  100  shown in  FIG. 2  in view of configuration and functions, except for the configurations of a hard case  320  and a thermal adhesion layer  350 . Thus, repetitive explanations will be omitted and the following description will be focused on the hard case  320  and the thermal adhesion layer  350 . 
         [0076]    Referring to  FIG. 6 , the hard case  320  can include a first hard case  330  and a second hard case  340 . The hard case  320  may be substantially the same as the hard case  120  shown in  FIG. 4 , except that the first hard case  330  of the hard case  320  may further include a first metal layer  334  formed on the inner surface thereof, and the second hard case  340  may further include a second metal layer  344  formed on the inner surface thereof. The first metal layer  334  and the second metal layer  344  can effectively prevent the electrolyte accommodated in the hard case  320  from leaking outside. In addition, the first metal layer  334  and the second metal layer  344  can prevent external moisture from being infiltrated into the hard case  320 . The strength of the hard case  320  against external impacts can further be enhanced. 
         [0077]    The thermal adhesion layer  350  may be substantially the same as the thermal adhesion layer  50  shown in  FIG. 3 , except that the thermal adhesion layer  350  may be larger than the thermal adhesion layer  50  shown in  FIG. 3  so as to couple the first hard case  330  including the first metal layer  334 , and the second hard case  340  including the second metal layer  344  to each other. 
         [0078]    As described above, in the secondary battery according to still another embodiment of the present invention, the first metal layer  334  and the second metal layer  344  may be further formed on inner surfaces of the first hard case  330  and the second hard case  340 , respectively, thereby effectively preventing charging and discharging operations from malfunctioning due to electrolyte leakage. In addition, it is possible to effectively prevent internal components from corroding due to infiltration of moisture. Further, the electrode assembly  10  can be protected from external impacts more efficiently. 
         [0079]    A secondary battery according to still another embodiment of the present invention will now be described. 
         [0080]      FIG. 7  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3 , for a secondary battery according to still another embodiment of the present invention. 
         [0081]    The secondary battery according to the current embodiment may be substantially the same as the secondary battery  100  shown in  FIG. 2  in view of configuration and functions, except for the configurations of a hard case  420  and a thermal adhesion layer  450 . Thus, repetitive explanations will be omitted and the following description will be focused on the hard case  420  and the thermal adhesion layer  450 . 
         [0082]    Referring to  FIG. 7 , the hard case  420  can include a first hard case  430  and a second hard case  440 . The hard case  420  may be substantially the same as the hard case  20  shown in  FIG. 3 , except that the first hard case  430  of the hard case  420  further includes a first thermal conduction layer  434  formed therein, and the second hard case  440  further includes a second thermal conduction  444  formed therein. 
         [0083]    Each of the first thermal conduction layer  434  and the second thermal conduction layer  444  may be formed by impregnating a thermally conductive material into a base having a high tensile strength and heat resistance. For example, each of the first thermal conduction layer  434  and the second thermal conduction layer  444  may be formed by impregnating ceramic powder into polymer fiber or non-woven fabric. The first thermal conduction layer  434  and the second thermal conduction layer  444  may reinforce the strength of the hard case  420  by using polymer fiber or non-woven fabric while preventing the temperature of the secondary battery from partially rising by transmitting the internal heat generated from the secondary battery evenly all over the hard case  420  using ceramic powder. 
         [0084]    The thermal adhesion layer  450  may be substantially the same as the thermal adhesion layer  50  shown in  FIG. 3 , except that the thermal adhesion layer  450  is larger than the thermal adhesion layer  50  shown in  FIG. 3  so as to couple the first hard case  430  including the first metal layer  434 , and the second hard case  440  including the second metal layer  444  to each other. 
         [0085]    As described above, in the secondary battery according to still another embodiment of the present invention, the first thermal conduction layer  434  and the second thermal conduction layer  444  may be further formed in the first hard case  430  and the second hard case  440 , respectively, thereby protecting the electrode assembly  10  from external impacts more efficiently. In addition, it is possible to prevent the life of the secondary battery from deteriorating due to a partial temperature rise. 
         [0086]    A secondary battery according to still another embodiment of the present invention will now be described. 
         [0087]      FIG. 8  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention. 
         [0088]    The secondary battery according to the current embodiment may be substantially the same as the secondary battery  100  shown in  FIG. 2  in view of configuration and functions, except for the configurations of a hard case  520  and a thermal adhesion layer  550 . Thus, repetitive explanations will be omitted and the following description will be focused on the hard case  520  and the thermal adhesion layer  550 . 
         [0089]    Referring to  FIG. 8 , the hard case  520  may include a first hard case  530  having a first bottom surface  531  and a first lateral surface  532 , and a second hard case  540 . The hard case  520  may be substantially the same as the hard case  20  shown in  FIG. 3 , except that the first hard case  530  of the hard case  520  is formed in a box shape, and the second hard case  540  is formed in a plate shape. 
         [0090]    The first hard case  530  and the second hard case  540  having the aforementioned configurations can facilitate alignment when they are coupled to each other. Here, the first hard case  530  may have a first lateral surface  532  with a height greater than a height of the first lateral surface  32  of the first hard case  30  shown in  FIG. 3 , providing for a first space  530   a  for accommodating the electrode assembly  10  entirely in the first hard case  530 . 
         [0091]    As described above, the secondary battery according to still another embodiment of the present invention can include the first hard case  530  that is box-shaped, and the second hard case  540  that is plate-shaped, thereby manufacturing the hard case  520  in a simplified manner. 
         [0092]    A secondary battery according to still another embodiment of the present invention will now be described. 
         [0093]      FIG. 9  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention. 
         [0094]    The secondary battery according to the current embodiment may be substantially the same as the secondary battery  100  shown in  FIG. 2  in view of configuration and functions, except for the configurations of a hard case  620  and a thermal adhesion layer  650 . Thus, repetitive explanations will be omitted and the following description will be focused on the hard case  620  and the thermal adhesion layer  650 . 
         [0095]    Referring to  FIG. 9 , the hard case  620  can include a first hard case  630  and a second hard case  640 . The hard case  620  may be substantially the same as the hard case  20  shown in  FIG. 3 , except that the first and second hard cases  630  and  640  of the hard case  620  have thicknesses of, for example, 0.3 mm or greater, which are smaller than the thicknesses of the first and second hard cases  30  and  40  shown in  FIG. 3 . This is because the first hard case  630  has an accommodating portion  634 , accommodating ends of lateral surfaces  642  of the second hard case  640  at contacting areas S where the first hard case  630  and the second hard case  640  contact. That is to say, a coupling structure of the first hard case  630  and the second hard case  640  can be securely supported by the accommodating portion  634 . Here, upper limits in thicknesses of the first hard case  630  and the second hard case  640  are not defined because the respective thicknesses of the first hard case  630  and the second hard case  640  may vary according to materials forming the same and usage of secondary battery manufactured. In detail, the accommodating portion  634  may have grooves  634   a  formed at ends of first lateral surfaces  632  so as to accommodate ends of the second hard case  640 . The ends of the second lateral surface  642  may form to correspond to the grooves  634   a  formed in the accommodating portion  634  so as to be smoothly accommodated in the grooves  634   a  of the accommodating portion  634 . 
         [0096]    The thermal adhesion layer  650  may be substantially the same as the thermal adhesion layer  50  shown in  FIG. 3 , except that the thermal adhesion layer  650  is accommodated in the groove  634   a  of the accommodating portion  634 . 
         [0097]    As described above, in the secondary battery according to still another embodiment of the present invention, the hard case  620  may be formed such that the first hard case  630  having the accommodating portion  634 , and the second hard case  640 , are formed thinly respectively, thereby increasing the size of the electrode assembly  10  in the secondary battery of the same size, ultimately increasing the battery capacity. 
         [0098]    Next, a secondary battery according to another embodiment of the present invention will be described. 
         [0099]      FIG. 10  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention. 
         [0100]    The secondary battery according to the current embodiment may be substantially the same as the secondary battery  100  shown in  FIG. 2  in view of configuration and functions, except for the configurations of a hard case  720 . Thus, repetitive explanations will be omitted and the following description will be focused on the hard case  720 . 
         [0101]    Referring to  FIG. 10 , the hard case  720  includes a first hard case  730  having a first bottom surface  731  and a first lateral surface  732 , and a second hard case  740  having a second bottom surface  741  and a second lateral surface  742 . 
         [0102]    The hard case  720  may be substantially the same as the hard case  20  shown in  FIG. 3 . However, in the first hard case  730  of the hard case  720 , each of first connection surfaces LS 3  and LS 4  of the first lateral surface  732  may have a rounded corner where each of the first connection surfaces LS 3  and LS 4  and the first bottom surface  731  meet, which would reduce unnecessary space from the first hard case  730  between the electrode assembly  10  and the first hard case  730 . The first connection surfaces LS 3  and LS 4  may be connected to a first lead-out surface LS 1  (shown in  FIG. 2 ), from which the first electrode tab  15  (shown in  FIG. 2 ) and the second electrode tab  16  (shown in  FIG. 2 ) are drawn out, and a first opposite surface LS 2  (shown in  FIG. 2 ) facing and opposite to the first lead-out surface LS 1 . In addition, a first inner surface  733  of the first hard case  730  may have a rounded inner profile that substantially matches the outer profile of the electrode assembly  10 . 
         [0103]    In addition, in the second hard case  740  of the hard case  720 , each of second connection surfaces SS 3  and SS 4  of the second lateral surface  742  may have a rounded corner where each of the second connection surfaces SS 3  and SS 4  and the second bottom surface  741  meet, which would reduce unnecessary space from the second hard case  740  between the electrode assembly  10  and the second hard case  740 . The second connection surfaces SS 3  and SS 4  may be connected to a second lead-out surface SS 1 , from which the first electrode tab  15  and the second electrode tab  16  are drawn out, and a second opposite surface SS 2  facing and opposite to the second lead-out surface SS 1 . In addition, a second inner surface  743  of the second hard case  740  may have a rounded inner profile that substantially matches the outer profile of the electrode assembly  10 . 
         [0104]    As described above, in the secondary battery according to another embodiment of the present invention, the hard case  720  having the aforementioned configuration is provided, including the first hard case  730  and the second hard case  740 , thereby increasing resistance against external impacts, reducing consumption of electrolyte due to an unnecessary space existing between the hard case  720  and the electrode assembly  10  and preventing the electrode assembly  10  from moving inside the hard case  720  by eliminating the unnecessary space. 
         [0105]    Meanwhile, although not illustrated in the drawing, the shape of the hard case  720  including the first hard case  730 , as shown in  FIG. 10 , may also be applied to the hard cases  120 ,  220 ,  320 ,  420 , and  620  shown in  FIGS. 4 ,  5 ,  6 ,  7 , and  9 , respectively. 
         [0106]    A secondary battery according to still another embodiment of the present invention will now be described. 
         [0107]      FIG. 11  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention. 
         [0108]    The secondary battery according to the present embodiment is substantially the same as the secondary battery  100  shown in  FIG. 2  with respect to its configuration and functions, except for features of a hard case  820 . Thus, repetitive explanations will not be provided and the following description will focus on the hard case  820 . 
         [0109]    Referring to  FIG. 11 , the hard case  820  may include a first hard case  830  having a first bottom surface  831  and a first lateral surface  832 , and a second hard case  40  having a second bottom surface  41  and a second lateral surface  42 . 
         [0110]    The hard case  820  in the present embodiment is substantially the same as the hard case  20  shown in  FIG. 3 , except that a first inner surface  833  of the first hard case  830  has a rounded inner profile that substantially matches the outer profile of an electrode assembly  10 . 
         [0111]    As described above, in the secondary battery according to still another embodiment of the present invention, the hard case  820  may include the first hard case  830  and the second hard case  40 , thereby reducing waste of electrolyte that may occur as a result of a dead space between the hard case  820  and the electrode assembly  10 , and preventing the electrode assembly  10  from moving inside the hard case  820  with the elimination of the dead space. 
         [0112]    Meanwhile, although not illustrated in the drawing, the shapes of the hard case  820  including the first hard case  830  and the second hard case  40 , as shown in  FIG. 11 , may also be applied to the hard cases  120 ,  220 ,  320 ,  420 , and  620  as shown in  FIGS. 4 ,  5 ,  6 ,  7 , and  9 , respectively. 
         [0113]    A secondary battery according to still another embodiment of the present invention will now be described. 
         [0114]      FIG. 12  is a sectional view illustrating components corresponding to those of the secondary battery shown in  FIG. 3  in a secondary battery according to still another embodiment of the present invention. 
         [0115]    The secondary battery according to the present embodiment is substantially the same as the secondary battery  100  shown in  FIG. 2  with respect to its configuration and functions, except for the features of a hard case  920 . Thus, repetitive explanations will not be provided and the following description will focus on the hard case  920 . 
         [0116]    Referring to  FIG. 12 , the hard case  920  may include a first hard case  830  having a first bottom surface  831  and a first lateral surface  832 , and a second hard case  940  having a second bottom surface  941  and a second lateral surface  942 . 
         [0117]    The hard case  920  in the present embodiment is substantially the same as the hard case  20  shown in  FIG. 3 , except that first and second inner surfaces  833  and  943  of the first and second hard cases  830  and  940  have rounded inner profiles that substantially match the outer profile of an electrode assembly  10 , respectively. 
         [0118]    As described above, in a secondary battery according to still another embodiment of the present invention, the hard case  920  may include the first hard case  830  and the second hard case  940 , thereby reducing waste of electrolyte that may occur as a result of a dead space between the hard case  820  and the electrode assembly  10 , and preventing the electrode assembly  10  from moving inside the hard case  920  by elimination of the dead space. 
         [0119]    Meanwhile, although not illustrated in the drawing, the shapes of the hard case  920  including the first hard case  830  and the second hard case  940 , as shown in  FIG. 12 , may also be applied to the hard cases  120 ,  220 ,  320 ,  420 , and  620  shown in  FIGS. 4 ,  5 ,  6 ,  7 , and  9 , respectively. 
         [0120]    Although the present invention has been described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that a variety of modifications and variations may be made to the present invention without departing from the spirit or scope of the present invention defined in the appended claims, and their equivalents.