Abstract:
According to an embodiment of the invention, a prismatic battery includes an electrode group  10  contained in a prismatic metal outer can. The electrode group  10  has a positive electrode substrate exposed part  11  at one end and a negative electrode substrate exposed part  12  at the other end. The positive and negative electrode substrate exposed parts  11  and  12  are bundled and welded to positive and negative electrode current collectors  13  and  14,  respectively. The positive electrode substrate exposed part  11  and positive electrode current collector 13 and the negative electrode substrate exposed part  12  and negative electrode current collector 14 are covered with an insulating frame  16  having an angled U-shaped cross section and an angled U-shaped outline. It is therefore possible to provide a prismatic battery of a simple structure including an electrode group whose ends are covered with an easily manufactured insulating cover in which the battery&#39;s volume energy density is maintained and an internal short circuit is prevented.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a prismatic battery, such as a lithium-ion or alkaline battery. More particularly, the invention relates to a prismatic battery including an electrode group contained in a prismatic metal outer can. The electrode group has a positive electrode substrate exposed part at one end and a negative electrode substrate exposed part at the other end. 
         [0003]    2. Related Art 
         [0004]    Lithium secondary batteries with high energy density (measured in Wh/Kg) have been developed as power sources for cellular phones, notebook computers, compact camcorders, and other mobile electronics and communications equipment, and for electric vehicles (EVs) and hybrid electric vehicles (HEVs). In particular, prismatic batteries have been attracting attention for their high volume energy density (measured in Wh/l). 
         [0005]    A typical method for manufacturing such prismatic batteries can be illustrated as follows. JP-A-2004-303500 is an example of related art. A positive electrode substrate typically made of aluminum foil is coated with a positive electrode mixture containing a positive electrode active material to make a strip positive electrode plate. A negative electrode substrate typically made of copper foil is coated with a negative electrode mixture containing a negative electrode active material to make a strip negative electrode plate. The strip positive and negative electrode plates are placed so as to face each other with a strip separator interposed therebetween to form a multilayer structure. This structure is rolled to make a flattened electrode group and contained in a prismatic metal outer can typically made of aluminum. Then a nonaqueous electrolyte is injected into the can, which completes a prismatic battery. 
         [0006]    The thus-manufactured flattened electrode group  20 , illustrated in  FIG. 5 , has a positive electrode substrate exposed part  21   a  (not coated with the positive electrode mixture) extended from the positive electrode plate at one end and a negative electrode substrate exposed part  21   b  (not coated with the negative electrode mixture) extended from the negative electrode plate at the other end. Welded to the side of the positive electrode substrate exposed part  21   a  is a positive electrode current collector  22  provided with a welded positive electrode lead  22   a . Welded to the side of the negative electrode substrate exposed part  21   b  is a negative electrode current collector  23  provided with a welded negative electrode lead  23   a.    
         [0007]    An insulator  24  is placed on the side of the positive electrode current collector  22 , while an insulator  25  is placed on the side of the negative electrode current collector  23 . Subsequently, the flattened electrode group  20  to which the positive and negative electrode leads  22   a  and  23   a  are welded is contained in a prismatic metal outer can  27 . The positive electrode lead  22   a  is welded to the lower end of a positive electrode terminal  26   a  on a sealing plate  26 , while the negative electrode lead  23   a  is welded to the lower end of a negative electrode terminal  26   b . The sealing plate  26  is welded to an opening edge of the metal outer can  27 . Then, a predetermined electrolyte is injected from an injection hole  26   c  on the sealing plate  26  and thereafter the hole  26   c  is plugged with an injection plug, which completes a prismatic battery. The sealing plate  26  also has a gas vent valve  26   d.    
         [0008]    With this prismatic battery disclosed in the related art, the positive and negative electrode substrate exposed parts  21   a  and  21   b  are exposed at both ends of the flattened electrode group  20 . This structure requires a clearance between the sides of the flattened electrode group  20  in its thickness direction and the inner wall of the metal outer can  27  in its thickness direction in order to prevent an internal short circuit between the exposed parts  21   a  and  21   b  via the outer can  27 . However, providing a clearance that is wide enough to prevent an internal short circuit means extra space in the battery, resulting in an undesirable decrease in the battery&#39;s volume energy density. 
         [0009]    In addition, since the insulator  24  is simply placed on the side of the positive electrode current collector  22  and the insulator  25  is simply placed on the side of the negative electrode current collector  23 , the positive and negative electrode substrate exposed parts  21   a  and  21   b  may come in contact with the metal outer can  27 , thereby causing an internal short circuit, if the battery falls and the flattened electrode group  20  moves, for example. This short circuit can be prevented by providing an insulating resin tape, for example, to the periphery of the flattened electrode group  20  including the outer surfaces of the insulators  24  and  25  and to the inner wall of the outer can  27 . 
         [0010]    This however causes another problem. Since the insulating resin tape has low mechanical strength, it may be broken or otherwise damaged when the flattened electrode group  20  provided with this tape is inserted into the metal outer can  27 , and as a result, comes in contact with the opening surface of the metal outer can  27 . Furthermore, providing this tape at more positions requires more work. In this case, the sides of the positive electrode current collector  22  including the positive electrode substrate exposed part  21   a  and of the negative electrode current collector  23  including the negative electrode substrate exposed part  21   b  may be covered by a resin molded piece. This molded piece, however, would be large in size, which increases the cost of parts and makes it difficult to have a reduced thickness, thereby lowering the battery&#39;s volume energy density. 
       SUMMARY 
       [0011]    An advantage of some aspects of the invention is to provide a prismatic battery of a simple structure including an electrode group whose ends are covered with an easily manufactured insulating cover, thereby maintaining the battery&#39;s volume energy density and preventing an internal short circuit. 
         [0012]    According to an aspect of the invention, a prismatic battery includes an electrode group contained in a prismatic metal outer can. The electrode group has a positive electrode substrate exposed part at a first end and a negative electrode substrate exposed part at a second end. The positive and negative electrode substrate exposed parts are bundled and welded to positive and negative electrode current collectors, respectively. The positive electrode substrate exposed part and positive electrode current collector and the negative electrode substrate exposed part and negative electrode current collector are covered with an insulating frame made of a resin sheet having an angled U-shaped cross section and an angled U-shaped outline. 
         [0013]    With the positive electrode substrate exposed part and positive electrode current collector and the negative electrode substrate exposed part and negative electrode current collector covered with the insulating frame having an angled U-shaped cross section and outline, the insulating frame protects the periphery of the electrode group, thereby preventing the electrode group from being damaged while it is inserted into the metal outer can. This structure also prevents an internal short circuit. Since the insulating frame made of a resin sheet can be made thin, no extra space is required, thereby increasing the battery&#39;s volume energy density. 
         [0014]    It is preferable that the insulating frame be bent along two first folding lines in a direction perpendicular to a longitudinal direction of the resin sheet to have an almost angled U-shaped outline, and the insulating frame be bent along two second folding lines in the longitudinal direction of the resin sheet to have an almost angled U-shaped cross section. This structure is simple and easy to manufacture, and therefore the insulating frame is provided economically. It is preferable that the resin sheet for the insulating frame be any one of polypropylene (PP), polyethylene (PE), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), and nylon. 
         [0015]    It is therefore possible to provide a prismatic battery including the insulating frame made of a resin sheet having an angled U-shaped cross section and outline provided around the electrode group in which the battery&#39;s volume energy density is maintained and internal short circuit is prevented. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
           [0017]      FIGS. 1A to 1C  schematically show a flattened electrode group according to one embodiment of the invention.  FIG. 1A  is a side view schematically showing the flattened electrode group to which a sealing plate is welded at its upper part.  FIG. 1B  is a plan view schematically showing a positive electrode current collector.  FIG. 1C  is a plan view schematically showing a negative electrode current collector. 
           [0018]      FIGS. 2A and 2B  schematically show an insulating frame according to the present embodiment.  FIG. 2A  is a plan view schematically showing a sheet material to be formed into the insulating frame.  FIG. 2B  is a perspective view schematically showing the sheet material bent to form the insulating frame. 
           [0019]      FIG. 3  is a side view schematically showing the flattened electrode group shown in  FIG. 1A  to which the sealing plate is welded at its upper part is being inserted into the insulating frame shown in  FIG. 2 . 
           [0020]      FIG. 4  is a side view schematically showing the flattened electrode group to which the insulating frame is fitted at its periphery and the sealing plate is welded at its upper part is being inserted into an outer can. 
           [0021]      FIG. 5  is an exploded perspective view schematically showing a related-art prismatic battery including a flattened electrode group. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0022]    An exemplary embodiment of the invention will be described with reference to  FIGS. 1 through 4 . It should be understood that the embodiment is not intended to limit the invention. Various changes and modifications can be made without departing from the spirit and scope of the invention.  FIGS. 1A to 1C  schematically show an electrode group according to one embodiment of the invention.  FIG. 1A  is a side view schematically showing the electrode group to which a sealing plate is welded at its upper part.  FIG. 1B  is a plan view schematically showing a positive electrode current collector.  FIG. 1C  is a plan view schematically showing a negative electrode current collector.  FIGS. 2A and 2B  schematically show an insulating frame according to the present embodiment.  FIG. 2A  is a plan view schematically showing a sheet material to be formed into the insulating frame.  FIG. 2B  is a perspective view schematically showing the sheet material bent to form the insulating frame.  FIG. 3  is a side view schematically showing the electrode group shown in  FIG. 1A  to which the sealing plate is welded at its upper part is being inserted into the insulating frame shown in  FIG. 2 .  FIG. 4  is a side view schematically showing the electrode group to which the insulating frame is fitted at its periphery and the sealing plate is welded at its upper part is being inserted into an outer can. 
       1. Positive Electrode Plate 
       [0023]    A positive electrode mixture is prepared by mixing  94 % by weight of lithium cobalt oxide (LiCoO 2 ) powders as a positive electrode active material and 3% by weight of carbonaceous powders, such as acetylene black or graphite, as a conductive agent. Separately, a binder solution is prepared by dissolving 3% by weight of a binder of polyvinylidene-fluoride (PVdF) with an organic solvent of N-methyl-2-pyrrolidone (NMP). Then, a positive electrode active material slurry is prepared by mixing and kneading the positive electrode mixture and the binder solution. As the positive electrode active material, LiCoO 2  may be replaced with lithium transition metal composite oxides represented by Li x MO 2  (M is at least one of Co, Ni, and Mn; 0.45≦x≦1.20), for example one or a combination of two or more of LiNiO 2 , LiNi y Co 1-y O 2  (0.01≦y≦0.99), Li 0.5 MnO 2 , and LiMnO 2 . 
         [0024]    A positive electrode substrate made of aluminum foil having a thickness of 20 μm, for example, is prepared. The above-described positive electrode active material slurry is applied evenly to one side of the positive electrode substrate to make a positive electrode mixture layer. Here, the end of the positive electrode mixture layer of a predetermined width (10 mm in this embodiment) is left uncoated with the slurry to make a positive electrode substrate exposed part  11  as shown in  FIG. 1 . Then, the resultant structure is passed through a dryer to remove an organic solvent (NMP) required for making the slurry. After being dried, the structure is extended to have a thickness of 0.06 mm with a rolling presser to make a strip positive electrode plate. The strip positive electrode plate is then cut out into a 96-mm wide strip, which completes a positive electrode plate having the positive electrode substrate exposed part  11  in a 10-mm wide strip shape. 
       2. Negative Electrode Plate 
       [0025]    A negative electrode active material slurry is prepared by mixing 98% by weight of natural graphite powders as a negative electrode active material and 1% by weight each of carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR) as binders and then by mixing and kneaded them with water. As the negative electrode active material, natural graphite may be replaced with carbonaceous materials that intercalate and deintercalate lithium ions, such as artificial graphite, carbon black, coke, glassy carbon, carbon fiber, or their calcined substances; metal lithium, lithium-aluminum alloy, lithium-lead alloy, lithium-tin alloy, or other lithium alloys; SnO 2 , SnO, TiO 2 , Nb 2 O 3 , or other metal oxides whose potentials are less noble than the positive electrode active material. 
         [0026]    A negative electrode substrate made of copper foil having a thickness of 12 μm, for example, is prepared. The above-described negative electrode active material slurry is applied evenly to one side of the negative electrode substrate to make a negative electrode mixture layer. Here, the end of the negative electrode mixture layer of a predetermined width (8 mm in this embodiment) is left uncoated with the slurry to make a negative electrode substrate exposed part  12  as shown in  FIG. 1 . Then the resultant structure is passed through a dryer. After being dried, the structure is extended to have a thickness of 0.05 mm with a rolling presser to make a strip negative electrode plate. The strip negative electrode plate is then cut out into a 98-mm wide strip, which completes a negative electrode plate having the negative electrode substrate exposed part  12  in an 8-mm wide strip shape. 
       3. Flattened Electrode Group 
       [0027]    The thus-manufactured positive and negative electrode plates are placed on top of each other with a strip separator interposed therebetween in a way that their center lines in the width direction coincide with each other. The strip separator is made of a microporous film that is 0.030 mm thick and 100 mm wide and has a polyethylene-polypropylene-polyethylene trilayer structure. The resultant structure is rolled with a winder and then the circumference is taped to make a rolled electrode group. This electrode group is pushed down to have a flattened cross section to make the flattened electrode group  10 . The flattened electrode group  10  has the positive electrode substrate exposed part  11  at one end (on the right of the electrode group  10  shown in  FIG. 1A ) and the negative electrode substrate exposed part  12  at the other end (on the left of the electrode group  10  shown in  FIG. 1A ). 
         [0028]    Referring to  FIG. 1B , a positive electrode current collector  13  made of aluminum having a rectangular body  13   a  and projecting parts  13   b ,  13   b  on both lower sides of the rectangular body, and a negative electrode current collector  14  made of nickel-plated copper having a rectangular body  14   a  and projecting parts  14   b ,  14   b  on both lower sides of the rectangular body are prepared. With the body  13   a  of the positive electrode current collector  13  pressed against the positive electrode substrate exposed part  11  at one end of the flattened electrode group  10 , the projecting parts  13   b ,  13   b  are bent and pressed to both sides of the positive electrode substrate exposed part  11 , and are irradiated with laser light to laser-weld the positive electrode substrate exposed part  11  and projecting parts  13   b ,  13   b . Accordingly, a laser welded portion  13   c  is formed in the projecting parts  13   b ,  13   b.    
         [0029]    With the body  14   a  of the negative electrode current collector  14  pressed against the negative electrode substrate exposed part  12  at the other end of the flattened electrode group  10 , the projecting parts  14   b ,  14   b  are bent and pressed to both sides of the negative electrode substrate exposed part  12 , and are irradiated with laser light to laser-weld the negative electrode substrate exposed part  12  and projecting parts  14   b ,  14   b . Accordingly, a laser welded portion  14   c  is formed in the projecting parts  14   b ,  14   b.    
         [0030]    A sealing plate  15  having a positive electrode terminal  15   a , a negative electrode terminal  15   b , an injection hole, and a gas vent valve (not shown) is prepared. The upper end of the body  13   a  of the positive electrode current collector  13  is bent and welded to the lower end of the positive electrode terminal  15   a , while the upper end of the body  14   a  of the negative electrode current collector  14  is bent and welded to the lower end of the negative electrode terminal  15   b . Accordingly, the sealing plate  15  is placed above the flattened electrode group  10 . Here, a resin insulator  15   c  is provided to insulate between the sealing plate  15  and the positive electrode terminal  15   a , and another resin insulator  15   d  is provided to insulate between the sealing plate  15  and the negative electrode terminal  15   b.    
         [0031]    4. Insulating Frame 
         [0032]    Referring to  FIG. 2A , a rectangular sheet material  16  made of polypropylene (PP) having two pairs of V-shaped notches  16   a ,  16   a  and  16   a ,  16   a  along its longer sides is prepared. The notches of each pair are on opposite sides facing each other. This sheet material is also provided with a pair of first folding lines  16   b ,  16   b  between the pairs of the notches  16   a ,  16   a , and a pair of second folding lines  16   c ,  16   c  connecting the apexes of the notches  16   a ,  16   a  on each side. Here, the length X between the first folding lines  16   b ,  16   b  is slightly longer than the length x of the bottom side of the flattened electrode group  10 . The length Y from each first folding line  16   b  to the adjacent end is slightly shorter than the length y from the bottom side of the electrode group  10  to the lower side of the sealing plate  15 . 
         [0033]    The sheet material  16  is bent inwardly at 90 degrees along the second folding lines  16   c ,  16   c . The sheet material  16  being bent along the second folding lines  16   c ,  16   c  is then bent inwardly at 90 degrees along the first folding lines  16   b ,  16   b . Accordingly, an insulating frame  16  having an angled U-shaped cross section and an angled U-shaped outline is formed as shown in  FIG. 2B . As a material for the sheet material  16 , polypropylene (PP) may be replaced with polyethylene (PE), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), or nylon. 
       5. Prismatic Nonaqueous Electrolyte Secondary Battery 
       [0034]    The flattened electrode group  10  provided with the sealing plate  15  at its upper part is inserted into the insulating frame  16 , having an angled U-shaped cross section and outline, from its opening side along its U-shaped outline. Consequently, the positive electrode substrate exposed part  11  and positive electrode current collector  13  and the negative electrode substrate exposed part  12  and negative electrode current collector  14  are covered with the insulating frame  16 . This insulating frame  16  protects the periphery of the electrode group  10 . 
         [0035]    In a mixed solvent prepared by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, 1 mol/liter of lithium hexafluorophosphate (LiPF 6 ) as an electrolyte is dissolved to prepare a nonaqueous electrolyte. Then the flattened electrode group  10  whose periphery is protected by the insulating frame  16  and whose upper part is provided with the sealing plate  15  is inserted into an aluminum prismatic outer can  17  from its opening. The contact parts of the outer can  17  and the sealing plate  15  are welded for airtight sealing. Then, the above-described nonaqueous electrolyte is injected from an injection hole on the sealing plate  15  and thereafter the hole is plugged with an injection plug, which completes a prismatic nonaqueous electrolyte secondary battery. 
         [0036]    As the electrolyte, LiPF 6  may be replaced with other lithium salts, such as lithium perchlorate (LiClO 4 ), lithium borofluoride (LiBF 4 ), lithium hexafluoroarsenate (Li 2 AsF 6 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), bis-trifluoromethane sulfonyl imide lithium [LiN(CF 3 SO 2 ) 2 ]. The amount of the electrolyte to be dissolved in an organic solvent is not limited to 1 mol/liter, and it preferably ranges from 0.5 to 2.0 mol/liter. 
         [0037]    According to the present embodiment, the insulating frame  16  having an angled U-shaped cross section and outline covers the positive electrode substrate exposed part  11  and positive electrode current collector  13  and the negative electrode substrate exposed part  12  and negative electrode current collector  14 . Since the insulating frame  16  protects the periphery of the flattened electrode group  10 , it is possible to prevent the electrode group  10  from being damaged while being inserted into the metal outer can  17 . It is therefore possible to further prevent an internal short circuit. Since the insulating frame  16  is made of a resin sheet, it can be made thin and no extra space is required in the outer can  17 , thereby increasing the volume energy density of the nonaqueous electrolyte secondary battery. 
         [0038]    While the invention is applied to a nonaqueous electrolyte secondary battery in the above-describe embodiment, it is not limited to this. It shall be understood that the invention is also applicable to nickel-hydride storage batteries, nickel-cadmium storage batteries, other alkaline storage batteries, and other types of storage batteries as long as they are prismatic batteries each having an electrode group provided with a positive electrode substrate exposed part at one end and a negative electrode substrate exposed part at the other end and contained in a prismatic metal outer can. In addition, while the rolled electrode group is pushed down to be a flattened electrode group in the above-described embodiment, the invention is applicable to any flattened electrode groups, including an electrode group in which flattened positive and negative electrode plates are placed on top of each other with a separator interposed therebetween.