Abstract:
A pouch, in which an electrode assembly of a battery is held, including a frame, including a groove into which the electrode assembly is inserted with a front of the electrode assembly temporarily exposed, upper and lower flanges bordering upper and lower ends of the groove, and extended parts on either side of the groove, front and upper sealing parts formed when the extended parts are folded over the front of the electrode assembly and the upper and lower flanges and sealed together and to the upper flange, respectively, the front and upper sealing parts defining a pocket in which an electrolyte solution is injected toward the electrode assembly, and a lower sealing part formed when the folded extended parts are sealed to the lower flange.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims the benefit of Korean Application No. 2005-134553, filed Dec. 29, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    An aspect of the present invention relates to a battery, and, more particularly, to a pouch-type battery using a pouch as an external case. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, a lithium secondary battery employs a non-aqueous electrolyte due to the reactivity of lithium with water. The non-aqueous electrolyte may be a solid polymer containing a lithium salt or a liquid in which a lithium salt is dissociated in an organic solvent. Lithium secondary batteries may be classified as either a lithium metal battery and a lithium ion battery, which use liquid electrolytes, or a lithium ion polymer battery, which uses a polymer electrolyte, depending upon types of the electrolyte employed by the batteries. 
         [0006]    A problem of leakage of an organic electrolyte can occur in a gel-type lithium ion polymer battery containing an organic electrolyte, while the problem does not occur in a solid-type lithium ion polymer battery. This leakage may be prevented by a relatively simple operating method for the lithium ion polymer battery, in comparison with that of a lithium ion battery using the liquid electrolyte. For example, in the lithium ion polymer battery, a multi-layered pouch including a metal foil and one or more polymer membranes, which cover top and bottom surfaces of the metal foil, are used instead of a metal can that is used in the lithium ion battery. 
         [0007]    When the multi-layered pouch is used, it is possible to reduce the weight of the battery, to reduce the thickness of the battery, and to relatively freely change the shape of the battery, in comparison with those cases in which the metal can is used. 
         [0008]      FIG. 1  is a perspective view of a conventional pouch-type lithium secondary battery illustrating a status in which a pouch is not sealed. As shown in  FIG. 1 , the conventional pouch-type lithium secondary battery includes an electrode assembly  30  and a pouch  20  to receive the electrode assembly. 
         [0009]    With reference to  FIG. 1 , in a general method of assembling a pouch-type lithium secondary battery, a middle portion of an approximately rectangular pouch membrane is folded to form a front side  21  and a rear side  22  of the pouch. A groove  223 , in which the electrode assembly  30  is accommodated, is formed on the rear side  22  by a process, such as a press working process. The indented portion  223  formed in this manner makes an installation of the electrode assembly  30  in post-processes possible, thereby making a performance of the assembling processes relatively easy. In addition, owing to the presence of the groove  223 , a sealing part of the pouch  20  around the groove  223  may be arranged, thereby allowing for a compact formation of the pouch. 
         [0010]    A multi-layered film, which is formed by sequentially stacking a positive electrode  31 , a separator  33 , and a negative electrode  35 , is wound in a spiral form to form the conventional electrode assembly  30  to form an arrangement resembling a jelly roll. When the jelly roll is formed by winding the multi-layered film, a separator is added to an external electrode surface that is exposed from the jelly roll or an internal electrode surface to prevent an occurrence of a short circuit between the positive electrode  31  and the negative electrode  36 . The formed jelly roll is disposed in the groove  223  of the rear side  22 , and the front and rear sides  21  and  22  of the pouch  20  are heated and pressed to form a bare cell of a battery while the front side  21  of the pouch  20  and a flange part  225 , which is flange shaped, of the rear side  22  of the pouch  20  are brought into tight contact with each other. 
         [0011]    Electrode taps  37  and  38  or electrode leads to electrically connect the positive and negative electrodes  31  and  35  of the electrode assembly  30  to an external circuit outside the pouch  20  are respectively formed in one side of the positive electrode  31  and one side of the negative electrode  35 . These electrode taps  37  and  38  are formed to be projected from the jelly roll in the direction perpendicular to the winding direction of the jelly roll and are drawn out through one side of the pouch  20  to be sealed. 
         [0012]    In the process of sealing the pouch  20 , a predetermined ingredient may be added to a surface of the polymer membrane to reinforce the bonding between the polymer membrane inside the pouch  20  and a metal constituting the electrode taps  37  and  38 . In addition, an insulating tape  39  may be further included to prevent an occurrence of a short circuit between the electrode taps  37  and  38  and the exterior frame of the pouch  20  before the pouch is sealed. 
         [0013]    Accessories or structures such as a protective circuit module (PCM) (not shown) or a positive temperature coefficient (PTC) (not shown) may be attached to the bare cell, of which the pouch has been sealed, to form a core cell. Thereafter, the core cell is inserted into a hard case to form a hard pack battery. Recently, in order to save space of the battery and to simplify the assembling process, a type of a battery has been developed, in which the external shape thereof is formed by closing both ends of a pouch of the battery in the longitudinal direction of the pouch and in which a circuit board and a protection member are attached to the pouch with a hot melt resin. In this type of battery a hard case is not required. 
         [0014]      FIG. 2  is a perspective view of a conventional pouch-type lithium secondary battery in a state in which edges of two sides of a bare cell that are opposed to each other from which the electrode taps are not drawn out, are folded.  FIG. 3  is an enlarged cross-sectional view of the conventional pouch-type lithium secondary battery taken along line A-A in  FIG. 2 . 
         [0015]    When a hard pack is formed without a folding of sealing parts  25  of the bare cell, or where, more particularly, the sealing parts  25  of two opposite sides from which the electrode taps  37  and  38  are not drawn out, an unnecessary space corresponding to the width of these portions is formed in the hard case. Accordingly, while the core pack is formed of the bare cell, both sealing parts  25  are folded toward the groove  223  in which the electrode assembly is disposed. When the pouch forms an external shape of the battery without an insertion of the pouch into the hard case, the sealing parts  25  of both sides of the pouch are folded to decrease the entire width of the battery in the same way as is described above. 
         [0016]    Accordingly, in the processes of assembling the conventional pouch, the groove  223  is first formed on the rear side  22  thereof. Thereafter, a flange part, which is an edge portion around the groove  223 , and an edge portion of the front side, which becomes a cover of the groove  223 , are welded to each other and sealed. Thereafter, the sealing parts  25 , on the opposite sides of the conventional pouch in the widthwise direction are bent toward the groove  223 . 
         [0017]    Recently, battery makers have been required to provide that two sides of the pouch are formed in a curved shape due to a problem in a design of a pouch-type battery or an electric or electronic device such as a cellular phone that is fitted with the pouch-type battery. Here, since the electrode assembly of the pouch-type battery has an elliptic or track shape and not an angled shape, when the sides of the pouch-type battery are formed in the curved shape, the electrode assembly fits inside the pouch-type battery substantially without any empty space. Accordingly, improvement in capacity-to-volume ratio of the battery may be expected. 
         [0018]    However, in the case of the conventional pouch in which the groove is formed, a portion forming the side walls of the groove and a flange part around the groove are approximately perpendicular to each other in a deep-drawing process to form the groove. In other words, angled corners are formed. When both sealing parts are bent toward the groove after the sealing, the bent portions form sharp corners due to the sharp corners which have already been formed in the rear side of the conventional pouch. Thus, it is difficult to form the sides of the pouch into a curved surfaces. Thus, the ratio of capacity to volume of the battery is decreased. 
         [0019]    In addition, the entire width of the bare cell of the battery is increased by the width (W+W=2W) of the sealing parts formed on both sides of the pouch. Accordingly, when the width of the battery is fixed to a predetermined value, increasing a space in a widthwise direction of the battery to receive the electrode plates and electrolyte required to increase the capacity of the battery is relatively difficult. In addition, in the subsequent processes, the sharp corners may be easily damaged due to contact with an external part. 
       SUMMARY OF THE INVENTION 
       [0020]    Aspects of the present invention provide a pouch-type battery and a method of assembling the pouch-type battery in which side walls of a pouch receiving an electrode assembly are formed in a curved surface. 
         [0021]    Aspects of the present invention also provide a pouch-type battery and a method of assembling the pouch-type battery, in which the capacity-to-volume ratio of the battery is enhanced. 
         [0022]    According to an aspect of the present invention, there is provided a pouch-type battery, comprising an electrode assembly, in which first and second electrodes, each comprising an electrode tap, and a separator interposed between the first and second electrodes are stacked and wound; and a pouch-type case including: a rear part having a side wall of a groove, in which the electrode assembly is disposed, a bottom surface of the groove, and a flange part extending from a first pair of opposite sides around the groove and a front part having two extended parts extending from a pair of second opposite sides around the groove, sides of the flange part being connected to the second pair of the sides to cover the electrode assembly disposed in the groove, wherein ends of the two extended parts overlap and are welded to form a front sealing part, and wherein the overlapped portion of the front sealing part over the flange part is at least partially welded to a corresponding portion of the flange part to form upper and lower sealing parts. 
         [0023]    In addition, while the two ends of the extended parts are overlapped with and welded to each other, a predetermined tensile force may be applied to the two ends so that a pulling force between the two ends is applied. In this case, forming the short sides in which the second pair of the sides is located as curved surfaces corresponding to an outer circumference surface of the electrode assembly is relatively easy. 
         [0024]    According to an aspect of the present invention, there is provided a method of assembling a pouch-type battery, the method comprising: preparing a pouch exterior frame having a groove, two flange parts which are located around the groove and which are opposed to each other, and two extended parts which are opposed to each other; winding and electrode assembly, including two electrodes having electrode taps and a separator interposed between the two electrodes; disposing the electrode assembly in the groove with the electrode taps being drawn out of the pouch exterior frame through one of the flange parts; partially overlapping and welding two ends of the two extended parts with each other on the electrode assembly to form a front sealing part; and forming a seal between at least one of the flange parts and the overlapped portion of the two extended parts. 
         [0025]    In addition, the method may further comprise injecting an electrolyte solution into an opening portion of the flange part and the overlapped portion of the two extended parts. 
         [0026]    Additional and/or other aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0028]      FIG. 1  is a perspective view of a conventional pouch-type lithium secondary battery illustrating a status in which a pouch is not sealed; 
           [0029]      FIG. 2  is a perspective view of a conventional pouch-type lithium secondary battery illustrating a status in which edges of two sides of a bare cell opposed to each other from which the electrode taps are not drawn out, are folded; 
           [0030]      FIG. 3  is an enlarged cross-sectional view of the conventional pouch-type lithium secondary battery taken along line A-A in  FIG. 2   
           [0031]      FIGS. 4 to 7  are state diagrams to illustrate an assembly of a pouch-type lithium secondary battery according to an embodiment of the present invention; and 
           [0032]      FIGS. 8 and 9  illustrate another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0033]    Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
         [0034]      FIGS. 4 to 7  are diagrams illustrating major processes for assembling a pouch-type lithium secondary battery according to an embodiment of the present invention. 
         [0035]      FIG. 4  illustrates an electrode assembly  30  disposed in a pouch exterior frame  40  having a groove  43 . The groove  43  includes a bottom and a pouch wall body forming four sides. The groove  43  is formed by a deep drawing process, so that corners where the bottom meets the sides form smooth curved surfaces. The groove  43  is formed in a shape of a plane rectangle, and flange parts  42  and  44  are formed around the pair of the short sides of the groove  43 , which are to be understood as the first pair of the four sides of the groove  43 . Two extended parts  46  and  48  are located on both sides of the pair of the long sides of the groove  43 , which are to be understood as the second pair of the four sides of the groove  43 , and flange parts  42  and  44  which are connected to the pair of the long sides of the groove  43 . The two extended parts  46  and  48  may be formed to have a same width. This shape may be formed by deep drawing a portion of the plane rectangular pouch exterior frame  40  corresponding in size to the groove  43 . 
         [0036]    Generally, a multi-layered membrane constituting the pouch includes a core part made of a metallic material, such as aluminum (Al), a heat fusion layer formed on an inner side of the core part, and an insulation membrane formed on an outer side of the core part. The heat fusion layer serves as an adhesive layer made of a modified polypropylene such as a casted polypropylene (CPP). The insulation membrane may be made of a resin material such as nylon and polyethylene terephthalate (PET). 
         [0037]    The electrode assembly  30  may have an elliptical or track-like shape so as to be similar to a conventional shape of an electrode assembly of a conventional rectangular battery. The electrode assembly  30  may be formed by winding two electrodes and a separator by a mandrel, so that the electrode assembly has a multi-layered structure comprising a separator, a first electrode, a separator, a second electrode or the first electrode, a separator, the second electrode, and a separator. 
         [0038]    Each electrode is formed by forming a slurry layer containing an active material on at least one side of a metal foil or a metal mesh comprising a current collection body in which a tap is combined with a portion of the current collection body for an electrical connection to an external circuit. 
         [0039]    In the first electrode of this embodiment, a first aluminum electrode tap  37 , which is projected a predetermined length from the electrode assembly  30 , is welded to a current collection body that is made of an aluminum (AL) material. In the second electrode, a second electrode tap  38 , which is generally made of a nickel (Ni) material, and which is projected a predetermined length from the electrode assembly  30 , is welded to a current collection body that is made of a copper material. An insulation tape is also provided to prevent a short circuit between the first electrode tap  37  or the second electrode tap  38  and the plane rectangular pouch exterior frame  40 . 
         [0040]    The first and second electrode taps  37  and  38  are drawn out of the pouch exterior frame  40 via an upper flange part  42  of the pouch exterior frame  40  and, then, are electrically connected to a protection circuit module (not shown) outside the pouch. 
         [0041]    The active material of the slurry layer, which is formed on at least one side of a current collection body of the first electrode, may comprise a chalcogenide compound, such as a mixed metal oxide selected from the group consisting of LiCoO 2 , LiMn2O 4 , LiNiO 2 , LiNi1-X CoXO 2  (0&lt;x&lt;1), and LiMnO 2 . An active material of the slurry layer, which is formed on at least one side of a current collection body of the second electrode, may be selected from the group comprising a carbon (C) based material, a silicon (Si), a tin (Sn), a tin oxide, a tin alloy composite, a transition metal oxide, a lithium metal nitride, or a lithium metal oxide. 
         [0042]    According to an embodiment of the invention, the electrode taps  37  and  38  pass through the upper flange part  42  in portions of the pouch exterior frame  40  through which the electrode taps  37  and  38  are drawn out. In this case, a resin tape, which is a type of an insulation tape, may be included in the portion through which the electrode tap is drawn out. 
         [0043]    As shown in  FIG. 4 , the pouch exterior frame  40  is bent along borders between a portion of the pouch exterior frame  40 , which includes the groove  43  of the pouch exterior frame  40  and flanges  42  and  44 , and the two extended parts  46  and  48 , so that the extended parts  46  and  48  cover the electrode assembly  30  in the groove  43 . Two ends  461  and  481  of the bent extended parts meet with each other and the upper flange part  42 , through which the electrode taps  37  and  38  are drawn out, and are welded to each other, so that an upper sealing part  52  and a front sealing part are formed as shown in  FIGS. 5A through 5C . In detail, the two ends  461  and  481  of the extended parts  46  and  48  are welded to each other, so that resin layers having a hot plate weldability, which are located in an inside of the pouch membrane, are opposed to each other as illustrated in  FIG. 5B , and a welded front sealing part  51  is folded so as to contact the other extended part of the pouch. Alternatively, the ends  461  and  481 , which are to be welded, of the two extended parts  46  and  48  may be disposed in opposition to each other, and the ends  461  and  481  are bent to contact a front side of the pouch. Thereafter, the ends  461  and  481  may be welded to each other. The welding of the two ends and the welding of the upper flange part  42 , through which the electrode taps are drawn out, may be performed in an arbitrary order or may be performed simultaneously. 
         [0044]    As shown in  FIG. 5C , when the two ends  461  and  481  of the extended portions  46  and  48  are welded to each other, the two ends  461  and  481  are then bent toward a middle portion of the pouch exterior frame  40 , with respect to a widthwise direction of the pouch exterior frame  40 , where the welding occurs, if the welding has not already been completed. In the process, the directions the two ends  461  and  481  each face are changed from a direction facing the outside of the pouch exterior frame  40  to a direction facing the pouch. Accordingly, an angled shape of a portion in which the groove is formed in the pouch exterior frame  40 , at which long sides of the groove  43  are connected to the extended parts  46  and  48  is straightened. Here, a curved surface having the same shape as the outer surface of the electrode assembly is formed in a long side portion of the groove  43  of the pouch exterior frame  40 , having the outer surface of the electrode assembly  30  as a reference for support, so that an entire side  53  of the pouch-type bare cell forms a curved surface. 
         [0045]    Referring to  FIG. 6 , a second sealing part (i.e., a lower sealing part) is disposed in a side opposite the first sealing part (i.e., an upper sealing part  52 ), through which the electrode taps  37  and  38  are drawn out. The second sealing part is not heat welded in the structure illustrated in  FIG. 5A  so that the second sealing part may act as a pathway to allow for a supplying of an electrolyte solution  60  into the electrode assembly  30  inside. Accordingly, the electrolyte solution  60  may be injected into the open second sealing part inside the pouch. 
         [0046]    In conventional pouch-type lithium batteries, the electrolyte solution is injected through the long side of the groove of the pouch. In such batteries, it is difficult for the injected electrolyte solution to flow into the interior of the electrode assembly since the electrolyte solution is blocked by at least one electrode plate. Thus, the electrolyte solution first moves into upper and lower sides of the electrode assembly and flows from the upper and lower sides of the electrode assembly into the inside of the electrode assembly through a gap between the separator and the electrodes. 
         [0047]    However, when the electrolyte solution  60  is injected into the open flange part, the upper or lower side of the electrode assembly  30  is reachable through the gap between the electrode plate and the separator. Accordingly, the electrolyte solution may flow relatively easily into inside of the electrode assembly  30 . In an alternative embodiment, a portion of the first sealing part  52 , through which the electrode taps are drawn out, may be open and the oppositely located second sealing part may be sealed. Here, the electrolyte solution is injected into the first sealing part  52  of the pouch  50 . 
         [0048]    Referring to  FIG. 7 , in a state in which the electrolyte solution is injected, as illustrated in  FIG. 6 , heat welding for the opening portion of the flange part is performed to form a lower sealing part  57 ′ so that the pouch is completely sealed from the exterior of the pouch. The lower sealing unit  57 ′ may then be bent to cover the bottom surface  55  in  FIG. 6 . In this case, since a cover composed of the lower sealing part  57 ′ includes two folds of the multi-layered membrane, the bottom surface portion, which comprises one fold of the multi-layered membrane, may be protected by the cover&#39;s support for the bottom surface portion of the pouch-type case. 
         [0049]      FIGS. 8 and 9  illustrate another embodiment of the present invention. In comparison with the embodiment illustrated in  FIG. 7 , the second sealing part  64 , which is located opposite to the first sealing part  72  of the upper portion is extended in a long direction thereof A gas room  81  is disposed in a portion of the extended part. The groove  63  in which the electrode assembly is disposed and the gas room  81  are connected with each other through a connection groove  85  formed in the second sealing part  64 . The connection groove  85  serves as a pathway through which the electrolyte solution is injected, and through which gas is collected into the gas room  81 . In order to form the connection groove  85 , a side wall  55  for a bottom side wall among the four side walls constituting the groove  63  is partially removed. The removed portion may be regarded as a groove of the side wall  55  formed on the bottom side wall and is hereinafter referred to an opening portion  552 . After the electrolyte solution is injected into an open lower flange part  64 , the pouch is sealed by welding a lower end  77  of the lower flange part  64 . The gas generated from an initial charging process is then collected into the gas room  81  formed in the lower flange part  64 . 
         [0050]    Thereafter, a final welding portion  79  of the lower flange part  64  of the pouch, which is adjacent to the groove  63 , is welded to form a lower sealing part. The gas room  81 , into which the gas generated by the initial charging process is collected, and the groove  63 , in which the electrode assembly is disposed, are each separated by the welding of the final welding portion  79 . A portion of the second flange part  64  located below the final welding portion  79  is then removed. As illustrated in  FIG. 9 , the final welding portion  79  is bent toward the bottom of the pouch, so that the lower sealing part  79 , which is the final welding portion, protects the bottom of the pouch. In this case, the lower sealing part  79  is bent so as to decrease the length of the pouch, thereby increasing the capacity-to-volume ratio of the battery to be assembled. 
         [0051]    The opening portion in this embodiment may be formed in the embodiments, in which the gas room is not formed, illustrated in  FIGS. 4 to 7 . The opening portion prevents the electrolyte solution from being injected unevenly, which may be caused by an injection of the electrolyte solution along the front side of the pouch-type case when the electrolyte solution is injected therein. In other words, the opening portion enables the electrolyte solution to infiltrate the interior of the electrode assembly  30  along the gap, which is formed through the entire bottom surface of the electrode assembly, between the electrode and the separator by evenly supplying of the electrolyte solution to the entire bottom surface, which is exposed through the opening portion, of the electrode assembly  30 . 
         [0052]    As shown in  FIG. 6 , a front sealing part  51 , which is located in a front side of the formed bare cell of the pouch, may be located between the two electrode taps  37  and  38 , which are drawn out of the pouch, in a widthwise direction of the pouch (i.e., a direction in which a first pair of sides is stretched) and may be located in a middle portion of the pouch. For example, generally a tap has a width of about 0.1 mm, and, thus, spaces between the electrode and the separator and between the electrode assembly and the wall body of the pouch in the widthwise direction of the pouch, respectively, are insufficient to allow for a fitting of a portion in which the tap is formed in the electrode assembly. Accordingly, the electrode taps are commonly disposed at positions separated from the electrode assembly so as not to overlap with each other. Two ends of the electrode assembly in the widthwise direction of the pouch form curved portions to reduce the space between the electrodes in the electrode assembly. On the other hand, the remaining portion in which the electrode tap is not located (i.e., a width portion between the electrode taps) has a comparatively sufficient space. Thus, when the front sealing part is disposed in the remaining portion from outside of the pouch, the substantial width of the secondary battery is relatively hardly increased. When the front sealing part  51  is formed, the side  73  of the pouch  70  forms a curved surface along the outer surface of the electrode assembly inside. 
         [0053]    Although the embodiments according to aspects of the present invention have been described mainly for the lithium secondary batteries, the present invention, except the initial charging/discharging process and the formation of the gas room, may be applied to all pouch-type batteries. 
         [0054]    Further, according to aspects of the present invention, a side of a pouch, which receives an electrode assembly, of the battery may be formed as a curved surface. Thus, relatively easy installation of the battery to an electric or electronic apparatus requiring a curved surface of the battery is possible. In addition, a side wall of the pouch is formed as a curved surface. Thus, receiving an electrode assembly having a cross-section of an ellipse or stadium shape without having an empty space is also possible. Thus, the width of the pouch, compared with a battery in which the sealing part of a pouch is located in the side of the pouch, is decreased, and the capacity of the battery over the volume is increased. In addition, directly injecting the electrolyte solution into top or bottom surfaces is possible, thereby reducing the time required to inject the electrolyte assembly. 
         [0055]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.