Patent Publication Number: US-2002010998-A1

Title: Process for the preparation of battery

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to a process for the preparation of a battery.  
       BACKGROUND ART  
       [0002] In recent years, electronic devices such as cellular phones, portable personal computers and portable video cameras have been developed, where the electronic devices are made into smaller and thinner portable ones. Under these circumstances, batteries to be incorporated in these electronic devices are required to have a high energy density.  
       [0003] As the batteries satisfying this requirement, there have been developed non-aqueous electrolyte secondary batteries, solid polymer secondary batteries and gel-like polyelectrolyte secondary batteries. These batteries are advantageous in that when they comprise a properly selected active material, they exhibit a voltage as high as  4  V or higher, a high energy density per unit weight, and can be available in a small size and light weight and an excellent cycle life performance and used repeatedly charged and discharged.  
       [0004] As the case for these batteries, there has heretofore been used a cylindrical or prismatic case made of a metal such as stainless steel, nickel-plated iron, aluminum, etc. Such a battery case has a high airtightness and an excellent mechanical strength. However, the heavy weight of the metallic material causes restrictions on the further reduction of the weight of batteries. In order to solve this problem and further reduce the weight and thickness of the battery, a method of receiving an electricity-generating element into a bag-shaped battery case has been put to practical use. For example, it has been practiced to prepare a thin secondary battery from a metal-laminated resin film having an airtight structure as a bag-shaped battery case. In this arrangement, a battery having a reduced weight and a high energy density per unit weight free from electrolyte leak and contamination of water from the exterior of the battery can be provided.  
       [0005] Such a thin secondary battery has heretofore been prepared, for example, as shown in FIGS.  11  to  14 . Lead members  101  and  103  are ultrasonically welded to positive and negative electrodes, respectively. The positive electrode and the negative electrode are then wound with a separator provided interposed therebetween into an ellipsoidal shape to prepare an electricity-generating element  105 .  
       [0006] Separately, as a battery case  107 , a flexible metal-laminated resin film having various layers such as PET (polyethylene terephthalate) layer, aluminum foil layer and PE (polyethylene) layer bonded each other is prepared. This film is folded with PE layer inside, and then heat-fused at both ends thereof and one side edge thereof to form a back sealed portion  109  and a bottom sealed portion  111 , respectively, forming a bag.  
       [0007] Subsequently, as shown in FIG. 11, the electricity-generating element  105  is inserted into the battery case  107  from its opening with the lead members  101  and  103  drawn from the electricity-generating element  105  being extending from the opening of the battery case  107 . An electrolytic solution is then injected into the interior of the battery case  107 . The edges of the opening of the battery case  107  are heat-sealed to each other to form a sealed portion  113  and hence seal the opening of the battery case  107 . In this manner, a thin secondary battery  115  was obtained as shown in FIGS. 12 and 13. The lead members  101  and  103  extend from the opening of the battery case  107  with a thermoplastic resin coat layer  117  interposed therebetween. In this arrangement, sealing of the battery case  107  is assured, making it possible to prevent electrolyte leak and contamination by water from the exterior of the battery. Further, in this thin secondary battery  115 , the lead members  101  and  103  which are outside the sealed portion  113  of the battery case  107  as they are form external terminals  119  and  120 , respectively.  
       [0008] The position of the external terminals  119  and  120  are decided depending on the position of the terminals of the electronic devices for which the thin secondary battery  115  is used. However, this preparation process is disadvantageous in that the position of the external terminals  119  and  120  relative to the battery case  107  can vary. This phenomenon is attributed to the following reasons. For example, as shown in FIG. 14, the battery case  107  is prepared somewhat larger than the electricity-generating element  105  so that it can easily receive the electricity-generating element  105 . Therefore, as shown in FIGS. 14A and 14B, the position of the electricity-generating element  105  thus inserted relative to the battery case  107  can deviate somewhat from the predetermined value. For example, as shown in FIG. 14A, the position of the electricity-generating element  107  relative to the battery case  107  deviates leftward from the predetermined value. As shown in FIG. 14B, the position of the electricity-generating element  107  relative to the battery case  107  deviates rightward from the predetermined value. This causes the position of the external terminals  119  and  120  relative to the battery case  107  to vary. Further, since the battery case  107  is made of a flexible laminated film, the position of the electricity-generating element  105  relative to the battery case  107  can easily vary, increasing the variation of the position of the external terminals  119  and  120 .  
       [0009] Moreover, when the lead members  101  and  103  are attached to the electrodes, the position of attachment can vary. In this case, because the lead members  101  and  103 , as they are, form the external terminals  119  and  120 , respectively, the variation of the attached position of the lead members  101  and  103  directly cause the position of the external terminals  119  and  120  to vary, respectively.  
       [0010] Moreover, when the positive electrode and the negative electrode with a separator interposed therebetween are worked to form an ellipsoidal shape, the position of the positive electrode and the negative electrode relative to each other can vary, resulting in the variation of the position of the external terminals  119  and  120 .  
       [0011] Due to these causes, the position of the external terminals  119  and  120  can vary, increasing the production of defectives during the production process.  
       SUMMARY OF THE INVENTION  
       [0012] It is therefore an object of the present invention to provide a battery having a reduced variation in the position of external terminals formed by lead members and hence stably-positioned external terminals.  
       [0013] The foregoing object of the present invention will become apparent from the following detailed description and examples.  
       [0014] The process for the preparation of a battery according to the present invention comprises the following steps. An electricity-generating element having a positive electrode lead member and a negative electrode lead member drawn therefrom is inserted into a battery case. The opening of the battery case is sealed with both the positive electrode lead member and the negative electrode lead member leading to the exterior thereof, so that the position of the battery case and the electricity-generating element relative to each other is fixed. The positive electrode lead member and/or the negative electrode lead member are worked into an external terminal with a predetermined position on the battery case as reference.  
       [0015] In accordance with the preparation process of the present invention, the opening of the battery case is sealed with both the positive electrode lead member and the negative electrode lead member leading to the exterior thereof, and the position of the battery case and the electricity-generating element relative to each other is fixed. In this manner, the position of the positive electrode lead member and the negative electrode lead member relative to the battery case can be fixed. In this fixed position, the position of the positive electrode lead member and the negative electrode lead member relative to the battery case can vary. In particular, in the case where the battery case is in the form of bag made of flexible metal-laminated resin film, the resulting variation in the position of the external terminals is great.  
       [0016] Accordingly, in accordance with the preparation process of the invention, after the positioning of the electricity-generating element relative to the battery case, the positive electrode lead member and/or the negative electrode lead member is/are worked with a predetermined position of the battery case as reference. In this manner, the position of the positive electrode lead member and the negative electrode lead member relative to the battery can be corrected to reduce its variation.  
       [0017] Of course, positioning can be tried when the electricity-generating element is inserted into the battery case or the positive electrode lead member and the negative electrode lead member are attached to the electrodes. However, it is very difficult and complicated to conduct positioning in all these procedures. Accordingly, in accordance with the preparation process of the present invention, the positive electrode lead member and/or the negative electrode lead member can be worked, making it possible to lessen the variation in position developed due to various causes prior to this working step. Thus, a very simple method can be used to lessen the variation of the position of the external terminals formed by the positive electrode lead member and the negative electrode lead member, making it possible to provide a battery having external terminals in stable positions. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0018] By way of example and to make the description more clear, reference is made to the accompanying drawings in which:  
     [0019]FIG. 1 is a plan view illustrating a positive electrode according to an embodiment of implication of the present invention;  
     [0020]FIG. 2 is a plan view illustrating a negative electrode according to an embodiment of implication of the present invention;  
     [0021]FIG. 3 is an exploded perspective view illustrating an electricity-generating element according to an embodiment of implication of the present invention;  
     [0022]FIG. 4 is a perspective view illustrating a process for winding an electricity-generating element according to an embodiment of implication of the present invention;  
     [0023]FIG. 5 is a perspective view illustrating an electricity-generating element and a battery case according to an embodiment of implication of the present invention;  
     [0024]FIG. 6 is a perspective view illustrating a sealed battery according to an embodiment of implication of the present invention;  
     [0025]FIG. 7 is a plan view illustrating a process for working a lead member according to an embodiment of implication of the present invention;  
     [0026]FIG. 8 is a plan view illustrating a process for working a lead member according to another embodiment of implication of the present invention;  
     [0027]FIG. 9 is a perspective view illustrating a battery in a completed form according to an embodiment of implication of the present invention;  
     [0028]FIG. 10 is a perspective view illustrating a battery according to another embodiment of implication of the present invention;  
     [0029]FIG. 11 is a perspective view illustrating a electricity-generating element and a battery case of the prior art;  
     [0030]FIG. 12 is a perspective view illustrating a battery in a completed form of the prior art;  
     [0031]FIG. 13 is a sectional view taken on the line A-A of FIG. 12; and  
     [0032]FIGS. 14A and 14B are plan views illustrating a battery in a completed form of the prior art. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0033] An embodiment of the preparation process according to the invention will be described with reference to an example shown in FIGS.  1  to  10 .  
     [0034] The battery prepared by the preparation process of the present invention comprises, for example, an electricity-generating element  50  received in a bag-shaped battery case  51 , said electricity-generating element  50  being formed by winding a belt-like positive electrode  10  and a belt-like negative electrode  20  with a separator  30  into a flat shape. The positive electrode  10  comprises an aluminum foil  12  as a current collector having a positive active material  14  (shown by the shade in FIG. 1) such as lithium cobalt oxide (LiCoO 2 ) coated on the both sides thereof as shown in FIG. 1. The negative electrode  20  comprises a copper foil  22  as a current collector having a negative active material  24  (shown by the shade in FIG. 2) such as graphite coated on the both sides thereof as shown in FIG. 2.  
     [0035] The aluminum foil  12  constituting the positive electrode  10  is free of positive electrode compound  14  at an end thereof to which a positive electrode lead member  16  made of aluminum is ultrasonically welded. The positive electrode lead member  16  extends upward from the electricity-generating element  50 . The copper foil  22  constituting the negative electrode  20  is free of negative electrode compound  24  at an end thereof to which a negative electrode lead member  26  made of nickel is ultrasonically welded. The negative electrode lead member  26  extends upward from the electricity-generating element  50 .  
     [0036] The positive electrode lead member  16  and the negative electrode lead member  26  are each coated with a thermoplastic resin coat layer  91  as shown in FIGS. 1 and 2 to assure that the thermoplastic resin coat layer  91  can be heat-fused to make airtight sealing.  
     [0037] The positive electrode lead member  16  and the negative electrode lead member  26  to be used herein have a width D 1  greater than the width D 2  of external terminals  81  and  83  of a completed battery shown in FIG. 9.  
     [0038] The positive electrode  10  and the negative electrode  20  are laminated on each other with a separator  30  provided interposed therebetween as shown in FIG. 3. As shown in FIG. 4, the laminate is then wound in such an arrangement that it is folded at a predetermined width from the end of the laminate to form a flat electricity-generating element  50 . In the wound form, the positive electrode compound  14  and the negative electrode compound  24  are opposed to each other with the separator  30  provided interposed therebetween. By impregnating the separator  30  with a nonaqueous electrolyte (e.g., 1:1:1 mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate having hexafluorinated lithium phosphate incorporated therein), a secondary lithium battery is formed.  
     [0039] Separately, as the battery case  51 , a flexible metal-laminated resin film is prepared by fusing various layers such as PET (polyethylene terephthalate) layer, aluminum foil layer and PE (polyethylene) layer to each other. The flexible metal-laminated resin film thus prepared is folded with PE layer being inside, and then heat-fused at both ends thereof and one side edge thereof to form a back sealed portion  53  and a bottom sealed portion  55 . Thus, a bag-shaped battery case is formed.  
     [0040] The electricity-generating element  50  is then received into the battery case  51  through the opening thereof. An electrolytic solution is then injected into the battery case. The opening of the battery case is closed, and the both edges of the opening is then pressure-bonded to each other under heating to seal the opening of the battery case  51 . As shown in FIG. 6, the both edges of the opening of the battery case  51  are bonded to each other with the positive electrode lead member  16  and the negative electrode lead member  26  interposed therebetween. By sealing the battery case  51  in this arrangement, the position of the electricity-generating element  50  relative to the battery case  51  is fixed. By punching the positive electrode lead member  16  such that the distance between the end  71  of the sealed portion  61  and the edges  73  and  74  of the positive electrode lead member  16  become predetermined values D 3  and D 4 , an external positive electrode terminal  81  is formed as shown in FIG. 7. Similarly, by punching the negative electrode lead member  26  such that the distance between the end  71  of the sealed portion  61  and the edges  75  and  76  of the negative electrode lead member  26  reach predetermined values D 5  and D 6 , an external negative electrode terminal  83  is formed. By the punching, undesirable portions  77 ,  78 ,  79  and  80  are removed. The predetermined distances D 3 , D 4 , D 5  and D 6  are determined depending on the width D 2  of the external terminals  81  and  83  and the predetermined position of the external terminals  81  and  83  from the end  71  of the sealed portion in a completed battery shown in FIG. 9. Thus, a battery  63  is prepared. In accordance with this preparation process, a battery having the external terminals  81  and  83  each in stable positions can be provided.  
     [0041] In some detail, as shown in FIGS. 7 and 8, when the electricity-generating element  50  is inserted into the battery case  51 , the position of the electricity-generating element  50  relative to the battery case  51  can deviate somewhat from the predetermined value.  
     [0042] In accordance with the preparation process of the present invention, after the positioning of the electricity-generating element  50  relative to the battery case  51 , the positive electrode lead member  16  and/or the negative electrode lead member  26  is/are worked with a predetermined position of the battery case  51  as reference. That is, at lease one of the positive electrode lead member  16  and the negative electrode lead member  26  is/are worked to have predetermined position(s) to the battery case and have predetermined size(s).  
     [0043] In any of the batteries  63  of FIGS. 7 and 8, the positive electrode lead member  16  is punched in such an arrangement that the distance between the end  71  of the sealed portion  61  and the edges  73  and  74  of the positive electrode lead member  16  are predetermined values D 3  and D 4 , respectively. Similarly, the negative electrode lead member  26  is punched in such an arrangement that the distance between the end  71  of the sealed portion  61  and the edges  75  and  76  of the negative electrode lead member  26  are predetermined values D 5  and D 6 , respectively.  
     [0044] In other words, the working is conducted in such an arrangement that the position of the external terminals  81  and  83  from the end  71  of the sealed portion  61  are fixed, making it possible to correct the variation of the position of the external terminals  81  and  83  developed during preparation.  
     [0045] The external terminals  81  and  83  may preferably have wide sections  84  and  85 , respectively, left unpunched at which they are drawn from the battery case  51 . By thus having the wide sections  84  and  85  left unpunched, the necessity of working the positive electrode lead member  16  and/or negative electrode lead member  26  up to a position close to the battery case  51  can be eliminated, facilitating the working and hence enhancing the productivity and making it unlikely that the battery case  51  can be damaged.  
     [0046] The working of the positive electrode lead member  16  and/or negative electrode lead member  26  is not specifically limited but may be accomplished by punching as mentioned above, or laser cutting, dimensional adjustment by folding or the like.  
     [0047] In another embodiment of implication of the present invention, the opening of the battery case  51  may be sealed with the external positive electrode terminal  81  and the external negative electrode terminal  83  uncoated with a resin coat layer  91  at the sealed portion  61  as shown in FIG. 10.  
     [0048] The preparation process of the invention can be widely used regardless of which the battery is primary or secondary.  
     [0049] The positive electrode material to be used in the invention is not specifically limited. In the case of secondary lithium battery, examples of the compound capable of absorbing/releasing lithium include an inorganic compound such as composite oxide represented by the composition formula Li x MO 2  or Li y M 2 O 4  (in which M represents a transition metal, x is from not smaller than 0 to not greater than 1 (0≦x≦1), and y is from not smaller than 0 to not greater than 2 (0≦y≦2)), oxide having tunnel-like pores and laminar metal chalcogenide or organic compound such as electrically-conductive polymer. These compounds may be used in admixture. Examples of the positive electrode materials employable herein include LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , Li 2 Mn 2 O 4 , MnO 2 , FeO 2 , V 2 O 5 , V 6 O 13 , TiO 2 , TiS 2 , and polyaniline.  
     [0050] The negative electrode material to be used in the invention is not specifically limited. In the case of secondary lithium battery, an alloy of lithium with Al, Si, Pb, Sn, Zn, Cd or the like, transition metal oxide such as LiFe 2 O 3 , WO 2  and MoO 2 , carbon-based material such as graphite and carbon, lithium nitride such as Li 5 (Li 3 N), metallic lithium foil, or mixture thereof may be used.  
     [0051] The electrolytic solution to be used in the invention is not specifically limited. In the case of secondary lithium battery, examples of the solvent for non-aqueous electrolytic solution include a polar solvent such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, y-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane and methyl acetate or mixture thereof.  
     [0052] Examples of the lithium salt to be dissolved in the organic solvent include a lithium salt such as LiPF 6 , LiClO 4 , LiBF 4 , LiAsF 6 , LiCF 3 CO 2 , LiCF 3 SO 3 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 CF 2 CF 3 ) 2 , LiN (COCF 3 ) 2  and LiN (COCF 2 CF 3 )  2  or mixture thereof.  
     [0053] Examples of the separating material such as separator include an insulating microporous polyethylene membrane impregnated with an electrolytic solution, solid polymer electrolyte, gel-like electrolyte comprising a solid polymer electrolyte having an electrolytic solution incorporated therein or combination of an insulating microporous membrane and a solid polymer electrolyte. In the case where a porous solid polymer electrolyte membrane is used as the solid polymer electrolyte, the electrolytic solution to be incorporated in the polymer and the electrolytic solution to be contained in the pores of the polymer may differ from each other.  
     [0054] The present invention is not limited to the embodiments described in the foregoing description in connection with the attached drawings. For example, the following embodiments can be included in the technical scope of the invention. Various changes and modifications can be made in the invention without departing from the spirit and scope thereof.  
     [0055] While the invention has been described in detail and with reference to the case where the electricity-generating element  50  is in a flat form, the electricity-generating element  50  may be in any other forms such as those having a circular or non-circular coil section, or laminate of flat electrodes with a separator provided interposed therebetween or folded material obtained by folding sheetlike electrodes with a separator provided interposed therebetween.  
     [0056] While the invention has been described in detail and with reference to the case where the battery case  51  is in the form of bag made of a flexible metal-laminated resin film, the present invention is not limited thereto and the battery case  51  may be obtained by vacuum-forming, air pressure-forming or pressure-forming a film or sheet.  
     [0057] While the invention has been described in detail and with reference to the case where both the positive electrode lead member  16  and the negative electrode lead member  26  are worked, either one of the positive electrode lead member  16  and the negative electrode lead member  26  may be worked.  
     [0058] While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.  
     [0059] This application is based on Japanese patent application No. 2000-226740 filed on Jul. 27, 2000, the entire contents thereof being hereby incorporated by reference.