JP2008103294A - Flat type battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat type battery capable of restraining short-circuiting failure between a cathode and an anode terminals and a thermal fusion part, without bringing forth manufacturing failure. <P>SOLUTION: The flat type battery is provided with a film-made vessel 1 having thermal fusion parts 21<SB>1</SB>to 21<SB>3</SB>at least at a part of its peripheral edge, a flat-shaped electrode group 8 housed in the vessel 1 containing cathodes 11 and anodes 15, a cathode terminal 16 electrically connected with the cathodes 11 and drawn out from the vessel 1 through the thermal fusion parts, and an anode terminal 17 electrically connected with the anodes 15 and drawn out from the vessel 1 through the thermal fusion parts. The cathode terminal 16 and the anode terminal 17 are equipped with slanted parts 22, respectively, getting thinner toward an end face at part located inside the thermal fusion part, with a microhardness of the slanted parts 22 of 1.5 times or more and 3 times or less of that of non-slanted parts 23. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flat battery.

  In recent years, with the development of electronic devices, lithium secondary batteries have been developed as non-aqueous electrolyte secondary batteries that are small, lightweight, have high energy density, and can be repeatedly charged and discharged. Recently, it is suitable for in-vehicle secondary batteries mounted on hybrid cars and electric cars, and secondary batteries for power storage used for power leveling. Development of a nonaqueous electrolyte secondary battery is desired. As such a secondary battery, for example, as described in Patent Document 1, lithium titanium oxide (lithium titanium composite oxide) having a small particle size (average particle size of primary particles is 1 μm or less) as a negative electrode active material. A non-aqueous electrolyte secondary battery that can be rapidly charged and discharged with high power and has excellent cycle performance has been developed.

  On the other hand, as an exterior member for housing the nonaqueous electrolyte secondary battery as described above, it is made of a laminate film having an aluminum foil and a thermoplastic resin film for the purpose of further reducing the thickness and weight in place of the conventional metal can. Attempts have been made to use containers and they have been put to practical use.

  A non-aqueous electrolyte secondary battery using such a film container is configured as follows, for example. A film having a rectangular concave portion (rectangular cup portion) produced by deep drawing, an edge portion extending horizontally in the four sides of the cup portion, and a flat plate portion connected to one of these edge portions. Use a container. In the cup portion of the container, a positive electrode capable of inserting and extracting lithium ions, a negative electrode, and a separator interposed between the positive and negative electrodes or an electrode group including a lithium ion conductive solid electrolyte layer are housed. Positive and negative terminals are connected to the positive and negative electrodes of this electrode group. The positive and negative terminals are extended outside the container through the edge. The flat plate of the container is bent 180 ° and heat-sealed to three edges excluding the edge connected to the flat plate, and the electrode group is hermetically sealed in the cup.

  The thermoplastic resin film constituting the film container needs to be thinned in order to make the battery thin. However, when the thermoplastic resin film is thinned, when the thermoplastic resin film is softened by the pressure at the time of thermal fusion, the thermoplastic resin film is pushed away by the thickness of the positive and negative electrode terminals, and the positive and negative electrode terminals and A metal foil such as aluminum constituting the film container is brought into contact, and short-circuit failure occurs. For this reason, even when the thermoplastic resin film is pushed away to some extent by the positive and negative electrode terminals at the time of heat fusion, an insulating resin layer having a sufficient thickness exists between the positive and negative electrode terminals and the metal foil of the container. An insulating film is disposed at a position corresponding to the fused portion of the positive and negative electrode terminals. As the insulating film, an acid-modified resin having good adhesion to metal is used.

  At this time, if the positive and negative electrode terminals have burrs or warps, there is a problem that even if an insulating film is used, the positive and negative electrode terminals and a metal foil such as aluminum in the container come into contact with each other and short circuit failure occurs.

  In particular, in recent years when non-aqueous electrolyte secondary batteries capable of rapid charging and high output discharge and excellent in cycle performance are developed, charging and discharging with a large current is required. In addition, large-sized batteries are applied to in-vehicle secondary batteries and secondary batteries for power storage used for power leveling. Therefore, these batteries require positive and negative terminals with lower resistance than before. Yes. That is, in order to realize low resistance, it is desirable to increase the current cross-sectional area, and a positive and negative electrode terminal that is thicker and wider than the conventional one is suitable. Such a situation is more likely to cause a short circuit failure between the positive and negative terminals and the container.

By the way, Patent Document 2 describes that the sealing performance at the end portion of the tab is improved by rounding or chamfering the corner portion of the tab of the polymer battery. When the corner of the tab is rounded or chamfered as in Patent Document 2, the strength of the corner is reduced, and thus the tab is likely to be chipped, warped, bent or the like in the battery manufacturing process.
JP-A-2005-123183 JP 2001-57203 A

  An object of the present invention is to provide a flat battery capable of suppressing a short circuit failure between the positive and negative electrode terminals and the heat-sealed portion without causing a manufacturing failure.

A flat battery according to the present invention comprises a film container having a heat fusion part by heat fusion at least a part of the periphery,
A flat electrode group that is housed in the container and includes a positive electrode and a negative electrode;
A positive electrode terminal electrically connected to the positive electrode and drawn from the container through the thermal fusion part;
A negative electrode terminal electrically connected to the negative electrode and drawn out from the container through the thermal fusion part,
Each of the positive electrode terminal and the negative electrode terminal has an inclined portion whose thickness decreases toward an end surface at a portion located in the heat-sealed portion, and the ultrafine hardness of the inclined portion is higher than that of the non-inclined portion. It is characterized by being 1.5 to 3 times the microhardness.

  ADVANTAGE OF THE INVENTION According to this invention, the flat battery which can suppress the short circuit defect between a positive-negative electrode terminal and a heat-fusion part can be provided, without causing a manufacturing defect.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the flat type non-aqueous electrolyte battery includes a film container 1. As shown in FIG. 3, the film container 1 extends from the rectangular cup portion 2, the edges 3 a to 3 c formed on the three open ends of the cup portion 2, and the remaining open ends of the cup portion 2. And a flat plate-like lid 4. The lid body 4 is used by being folded back to the cup portion 2 side. As shown in FIG. 2, the film container 1 is formed by laminating a thermoplastic resin film 5 constituting an inner surface of the container 1, a metal foil 6 such as an aluminum foil, and a rigid organic resin film 7 in this order. It is formed from a laminate film.

As shown in FIG. 3, the flat electrode group 8 is housed in the cup portion 2 of the film container 1. As shown in FIG. 2, the flat electrode group 8 includes a current collector 14 between a positive electrode 11 having a structure in which a current collector 10 is interposed between positive electrode layers 9 and 9, a separator 12, and negative electrode layers 13 and 13. The negative electrode 15 and the separator 12 having a structure in which a metal is interposed are spirally wound into a substantially cylindrical shape, and then flattened by, for example, pressure molding at room temperature under a pressure of 10 to 30 kg / cm ^2. It is produced by. The strip-like positive electrode terminal 16 is electrically connected to the positive electrode 11 of the electrode group 8. On the other hand, the strip-like negative electrode terminal 17 is electrically connected to the negative electrode 15 of the electrode group 8. The tips of the positive electrode terminal 16 and the negative electrode terminal 17 extend from the same end surface of the electrode group 8 and are drawn out through the short side edge 3 c of the cup portion 2 in the container 1.

  As shown in FIG. 3, the strip-shaped insulating film 18 a is interposed between the short side edge 3 c of the cup 2 in the container 1 and the positive and negative terminals 16 and 17. On the other hand, as shown in FIG. 3, the strip-shaped insulating film 18 b is disposed at a location facing the edge 3 c on the inner surface of the lid 4. As shown in FIG. 2, the insulating films 18a and 18b are in contact with the positive and negative terminals 16 and 17, and are melted at the time of heat-sealing and are in close contact with the positive and negative terminals 16 and 17, respectively. It has a two-layer structure that is laminated on one resin film 19 and is composed of a second resin film 20 having a higher melting point than that of the first resin film 19.

The lid body 4 in the film container 1 is folded back to the cup portion 2 side, and the three edges 3a to 3c of the cup portion 2 and the lid body 4 are heat-sealed. The long side edge portions 3a and 3b and the lid 4 are heat-sealed by the thermoplastic resin film 5 located on the inner surface thereof to form heat-sealed portions 21 ₁ and 21 ₂ . As shown in FIG. ₁ , the heat fusion portions 21 ₁ and 21 ₂ are bent inward by 90 ° toward the cup portion 2. Short side edge 3c and the cover 4, in the meantime, the insulating film 18a, positive and negative terminals 16, 17 and the insulating film 18b is thermally fused in a state of being interposed, heat-sealed portion 21 ₃ is formed . The flat electrode group 8 is hermetically sealed in the container 1 by the heat fusion portions 21 _{1 to} 21 ₃ . The nonaqueous electrolyte is accommodated in the cup portion 2 of the container 1.

Next, the positive and negative terminals 16 and 17 will be described with reference to FIGS. Positive and negative terminals 16 and 17, (in the case of FIG. 5, the longitudinal direction) withdrawing direction molded crush the portion located thermally fused portion 21 ₃ of the parallel end faces is applied. As crushing molding, for example, press molding or roll molding can be employed. Press molding is easier. The portion subjected to the crush molding is stretched in the width L direction of the positive and negative electrode terminals 16 and 17 and has an inclined structure in which the thickness decreases toward both end faces as shown in FIGS. (Hereinafter referred to as the inclined portion 22). The ultra micro hardness of the inclined portion 22 is 1.5 times or more and 3 times or less of the ultra micro hardness of the non-inclined portion (non-molded portion) 23. The reason for this will be explained. If the ratio is less than 1.5 times, the positive and negative terminals 16 and 17 may be defective, warped, bent, or the like in the battery manufacturing process, particularly in the heat fusion process. Moreover, since the burr | flash and curvature which a positive / negative electrode terminal has are crushed and it is easy to remain after shaping | molding, a metal foil like aluminum of a film-made container contacts, and a short circuit defect arises. On the other hand, if the ratio exceeds three times, the thickness of the end face of the inclined portion 22 becomes thin, and thus the positive and negative terminals 16 and 17 are chipped, warped, bent, etc. in the battery manufacturing process, particularly in the heat fusion process. By making the ultra micro hardness of the inclined portion 22 1.5 times or more and 3 times or less than the ultra micro hardness of the non-inclined portion, both of manufacturing defects and short circuit defects can be avoided.

  The ultra-micro hardness is a hardness calculated from a test load and an indentation depth by placing an indenter on a sample, increasing the load at a constant speed, holding the load for a certain time after reaching a specified load. Specifically, it is measured by the method described in Examples described later.

The length Lp of the inclined portion 22 desirably satisfies L _p ≦ 10T ₀ when the thickness of the positive and negative terminals 16 and 17 is T ₀ . When L _p exceeds 10T ₀ , the strength of the tip surface where the inclined portion 22 is the thinnest is insufficient, and the positive and negative terminals 16 and 17 are missing, warped, bent, etc. in the battery manufacturing process, particularly in the heat sealing process. May cause defects. The lower limit value of Lp is desirably 5T ₀ . This is because when Lp is less than 5T ₀ , the resin film softened by heat fusion is not easily adapted to the shape of the positive and negative electrode terminals, and the adhesion between the positive and negative electrode terminals and the resin film is lowered. This is because gaps (bubbles) may be generated in the portion. By setting Lp to 5T ₀ ≦ L _p ≦ 10T ₀ , it is possible to further increase the sealing strength of the heat-sealed portion and to reduce manufacturing defects.

A method for measuring the length Lp of the inclined portion 22 will be described. In the optical micrograph (for example, FIG. 9) of the surface of the portion located in the heat fusion part 21 ₃ of the positive and negative terminals 16 and 17, the inclined part 22 has lower brightness than the non-inclined part 23, and the inclined part 22 And a non-inclined portion 23 has a boundary based on a difference in brightness. The maximum value of the distance from the boundary X to the end face Y of the inclined portion 22 is defined as a length Lp.

The thickness Tp of the end surface of the inclined portion 22, it is desirable to Tp ≦ T _0/2. If the thickness Tp is greater than T _0/2, hardly familiar softened the shape of the resin film positive and negative terminals by thermal fusion, the adhesion between the positive and negative terminals and the resin film is reduced, heat-sealed portion A gap (bubble) may be generated in the (seal part). By the Tp ≦ T _0/2, can be a seal strength of heat-sealing unit positive and negative terminals 16, 17 are interposed between sufficient. However, when the thickness Tp is less than 10 μm, the strength of the end face of the inclined portion 22 may be insufficient. Therefore, in order to make the strength of the seal strength between the inclined portion 22 of the heat-sealed portion in sufficient, it is more preferable that the thickness Tp to _{10μm ≦ Tp ≦ T 0/2} .

Note that T ₀ is the thickness of the positive electrode terminal 16 when the length Lp and the thickness Tp of the inclined portion 22 of the positive electrode terminal 16, and T ₀ is the case of the length Lp and the thickness Tp of the inclined portion 22 of the negative electrode terminal 17. Is the thickness of the negative electrode terminal 17. The thickness of the positive electrode terminal 16 and the negative electrode terminal 17 can be in the range of 50 μm or more and 500 μm or less, respectively. The thicknesses of the positive electrode terminal 16 and the negative electrode terminal 17 may be the same or different from each other.

The length Ln (the length in the direction orthogonal to Lp) of the inclined portion 22 may be equal to the width Ls of the heat-sealing portion 21 _{3 or} may be longer than the width Ls. When longer than the width Ls, the difference between the length Ln and the width Ls is desirably 2 mm or less.

  The material of the positive and negative terminals 16 and 17 is preferably aluminum or an aluminum alloy. By selecting this material, the strength of the terminal can be increased by crushing molding. The aluminum alloy preferably contains at least one element selected from the group consisting of Cu, Mn, Mg, and Cr.

  Next, a method for manufacturing a flat battery according to the present invention will be described below.

  First, the rectangular cup portion 2 is formed by deep drawing a laminate film obtained by laminating a thermoplastic resin film, a metal foil, and a rigid organic resin film in this order. Subsequently, the laminate film is cut so that one side of the opening of the rectangular cup part 2 is located at the center, and the narrow edges 3a to 3c extending horizontally in the four sides around the cup part 2 and The film container 1 is obtained by cutting out so as to form a wide edge (lid) having a wide width (the same width as the combined length of the cup 2 and the second edge 3c). Next, strip-shaped insulating films 18 a and 18 b are thermally fused to the edge 3 c of the film container 1 and the inner surface of the lid 4, respectively. The insulating films 18 a and 18 b are in contact with the positive and negative terminals 16 and 17, and are laminated on the first resin film 19 and a first resin film 19 that melts and adheres closely to the positive and negative terminals 16 and 17 during heat fusion. And has a two-layer structure including the second resin film 20 having a higher melting point than the first resin film 19.

Next, the flat electrode group 8 having the positive and negative terminals 16 and 17 is accommodated in the cup portion 2 of the film container 1 so that the positive and negative terminals 16 and 17 extend from the edge 3c to the outside. Subsequently, the lid body 4 of the film container 1 is bent by 180 °, the lid body 4 and the edges 3a to 3c are overlapped, and the two edges 3b and 3c are heat-sealed while being pressed at a desired pressure. At this time, the insulating films 18a and 18b are thermally fused to both surfaces of the positive and negative terminals 16 and 17, respectively, at the edge 3c from which the positive and negative terminals 16 and 17 extend and the lid body 4, and the positive and negative terminals 16, In the region excluding 17, the insulating films 18 a and 18 b are heat-sealed. Further, the thermoplastic resin films of the film container 1 are heat-sealed at the edge 3 b and the lid 4. Thereafter, the nonaqueous electrolytic solution is injected into the cup portion 2 through the gap between the non-thermally bonded edge portion 3a and the lid body 4, and the electrode group 8 accommodated therein is impregnated with the nonaqueous electrolytic solution. Subsequently, after the non-heat-sealed portion is heat-sealed and the flat electrode group 8 is hermetically sealed, the heat-sealed portions 21 ₁ and 21 ₂ are cut to a desired width and bent toward the cup portion 2. Thus, the flat battery shown in FIGS. 1 to 3 described above is manufactured.

  The arrangement of the insulating film in the flat battery described above is not limited to the form shown in FIG. For example, as shown in FIG. 8, insulating films 24 and 25 may be disposed at locations facing each surface of the positive electrode terminal 16 and locations facing each surface of the negative electrode terminal 17, respectively.

  Moreover, as shown in FIGS. 1-3 and 8, after fixing an insulating film to a cover body and an edge part, you may heat-seal a cover body and an edge part, but an insulating film is attached to a cover body and an edge part. Instead of fixing, it is also possible to fix to the positive and negative terminals. In this invention, since the inclination part (crush molding part) is formed only in the part located in a heat-fusion part, positioning of the insulating film to a positive / negative electrode terminal can be performed easily.

  The heat-sealing portion may be formed on a part of the peripheral edge of the container as shown in FIG. 3 described above, but it can also be formed on the entire peripheral edge of the container.

  In FIG. 1 described above, the positive and negative electrode terminals 16 and 17 are drawn out from the same heat fusion part of the container 1, but the positive electrode terminal 16 is drawn out from one of the heat fusion parts and positioned on the opposite side of the heat fusion part. The negative electrode terminal 17 may be drawn out from the heat-sealed part.

  Hereinafter, the film container 1, the positive electrode 11, the separator 12, the negative electrode 15, the nonaqueous electrolyte, and the insulating films 18a and 18b will be described.

1) Container made of film Examples of the thermoplastic resin film constituting the container made of film include polyethylene (PE) film, polypropylene (PP) film, polypropylene-polyethylene copolymer film, ionomer film, and ethylene vinyl acetate (EVA) film. Etc. can be used.

  As the metal foil constituting the film container, for example, an aluminum foil can be used.

  As the organic resin film having rigidity that constitutes the film container, for example, a polyethylene terephthalate (PET) film, a nylon film, or the like can be used.

2) Positive electrode The positive electrode has a structure in which a positive electrode layer containing an active material and a binder is supported on both surfaces (or one surface) of a current collector.

  Examples of the current collector include aluminum, nickel or stainless steel plates, aluminum, nickel or stainless steel meshes, and the like.

Examples of the active material include various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel cobalt oxide, lithium-containing iron oxide, and vanadium containing lithium. Examples thereof include chalcogen compounds such as oxides, titanium disulfide, and molybdenum disulfide. Among them, it is preferable to use lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or lithium manganese oxide (LiMn ₂ O ₄ or LiMnO ₂ ) because a high voltage can be obtained.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-gen copolymer (EPDM), and styrene-butadiene rubber (SBR).

  The positive electrode layer contains a conductive agent such as acetylene black, carbon black, and graphite.

  The positive electrode layer preferably has a thickness of 3 to 6 times that of the current collector by single-sided coating (single-sided support).

3) Separator The separator is made of, for example, a microporous film made of polyethylene, polypropylene, an ethylene-propylene copolymer, an ethylene-butene copolymer, or a woven or non-woven fabric having fibers of these materials.

4) Negative electrode This negative electrode has a structure in which a negative electrode layer containing an active material and a binder is supported on (or on one side of) a current collector.

  Examples of the current collector include a copper plate and a copper mesh.

  The active material is not particularly limited, but is lithium metal, lithium alloy, or coke, carbon fiber, graphite, mesophase pitch carbon, pyrolysis gas, which reversibly occludes / releases or intercalates lithium ions during charge / discharge. Examples thereof include carbonaceous materials such as phase carbonaceous materials and resin fired bodies.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-gen copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. It is preferable to contain this binder.

  It is preferable that the negative electrode layer has a thickness of 3 to 6 times by single-sided coating (single-sided support) with respect to the current collector.

5) Nonaqueous electrolyte As this nonaqueous electrolyte, a nonaqueous electrolyte, a gel-like nonaqueous electrolyte, etc. can be used, for example. The nonaqueous electrolytic solution includes an electrolyte and a nonaqueous solvent in which the electrolyte is dissolved.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium hexafluoroarsenate (LiAsF ₆ ), and lithium trifluoromethanesulfonate. (LiCF ₃ SO ₃ ), LiN (CF ₃ SO ₂ ) ₂ or the like can be used.

  Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; cyclic esters such as γ-butyrolactone; tetramethylsulfolane, dimethyl sulfoxide, N-methylpyrrolidone, dimethylformamide, and derivatives thereof. Non-aqueous solvents, etc. can be used. These non-aqueous solvents can be used in the form of one kind or a mixture of two or more kinds. Furthermore, the viscosity of the non-aqueous electrolyte can be obtained by mixing these non-aqueous solvents with a chain carbonate such as dimethyl carbonate, methyl ethyl carbonate or diethyl carbonate, or a solvent such as acetonitrile, ethyl acetate, methyl acetate, toluene or xylene. Can be lowered.

  The concentration of the electrolyte in the non-aqueous solvent is preferably 0.5 mol / L or more.

  In the flat battery according to the present invention, a solid electrolyte may be used instead of the separator. However, in the flat battery having such a configuration, the nonaqueous electrolyte is held by the positive and negative electrodes and the solid electrolyte, respectively.

6) Insulating films 18a and 18b
As described above, the insulating films 18 a and 18 b each have a two-layer structure including the first resin film 19 and the second resin film 20.

  It is desirable to make the melt flow rate (MFR) of the second resin film 20 lower than the MFR of the first resin film. According to such a configuration, when the first resin film (high MFR and good flow characteristics of the resin film at the time of fusion) out of the insulating films in contact with the positive and negative terminals is positive or negative when melted by heat fusion. A good resin flow can be formed along the inclined portion of the electrode terminal. In particular, the second resin film 20 preferably has a melt flow rate (MFR) of 2 g / 10 minutes.

  That is, in order for the positive and negative electrode terminals and the insulating film to be in close contact with each other, it is necessary to sufficiently soften the resin film around the positive and negative electrode terminals so as to conform to the shape of the positive and negative electrode terminals. At this time, the inclined portions of the positive and negative electrode terminals on both end surfaces function effectively, and no gaps (bubbles) are generated in the heat-sealed portion (seal portion), and a favorable seal can be formed. Further, by forming a good resin flow as described above, the mixing between the layers of the resin film due to the convection between the first and second resin films generated at the time of heat fusion is reduced, and the second resin The function as the protective layer of the film is sufficiently maintained, and a short circuit due to contact between the metal foil of the film container and the positive and negative terminals can be prevented.

  In the insulating film having a two-layer structure having a low MFR of the second resin film, (a) an acid-modified polyethylene layer and a polyethylene layer are arranged, and the acid-modified polyethylene layer is disposed on the side in contact with the positive and negative electrode terminals, or (b It is preferable that the acid-modified polypropylene layer is disposed on the side in contact with the positive and negative electrode terminals.

  The acid-modified polyethylene is preferably, for example, acid-modified low-density linear polyethylene or acid-modified linear polyethylene.

  The polyethylene is preferably, for example, medium density or high density polyethylene.

  The polypropylene is preferably, for example, a homopolymer-based polypropylene.

  The acid-modified polypropylene is preferably a random copolymer-based polypropylene, for example.

[Example]
Embodiments of the present invention will be described below with reference to the drawings described above.

(Example 1)
<Production of film container>
Depth processing is applied to a laminate film with a total thickness of 0.095 mm composed of 0.025 mm thick nylon film / 0.04 mm thick aluminum foil / 0.03 mm thick polyethylene film to a depth of 3 A rectangular cup portion 2 having a length of 0.0 mm, a length of 54 mm, and a width of 34 mm was formed. Next, by cutting the laminate film, as shown in FIG. 3 described above, the edges 3a to 3c having a width of 5 mm extending horizontally on the three sides around the cup portion 2 and a width of 60 mm on the remaining one side. A film container 1 having a lid 4 and having an outer dimension of 170 mm × 130 mm was produced.

  Next, a 0.07 mm thick first resin film made of acid-modified linear low density polyethylene (acid-modified LLDPE) having a melting point of 120 ° C. and MFR of 1.7 g / min, a melting point of 130 ° C. and MFR of A two-layer film having a total thickness of 0.12 mm made of 0.6 g / min high-density polyethylene (HDPE) and laminated with a second resin film having a thickness of 0.05 mm, has a width of 5 mm and a length of 30 mm. Two strip-shaped insulating resin films (insulating films) were produced. Subsequently, as shown in FIG. 3 described above, these insulating films 18 a and 18 b were arranged on the edge 3 c of the film container 1 and the inner surface of the lid 4. At this time, the second resin film made of HDPE of the insulating films 18 a and 18 b was disposed so as to contact the inner surface of the container, and was heat-sealed to the film container 1.

<Preparation of end crushing electrode terminal>
A strip-shaped aluminum positive electrode terminal and negative electrode terminal having a thickness T ₀ of 0.1 mm and a width L of 4 mm were prepared. About each, it crush-molded with the press in the location located in a heat-fusion part among the both end surfaces of a longitudinal direction side. FIG. 9 shows an optical micrograph of the inclined portion (crushed molding portion). As shown in FIG. 9, a boundary X based on the difference in brightness exists between the inclined portion 22 and the non-inclined portion 23. The maximum value of the distance from the boundary X to the end face Y of the inclined portion 22 is the length Lp. The length Lp was 0.8 mm. Since the thickness T ₀ of the positive and negative electrode terminals is 0.1 mm, 5T ₀ ≦ L _p ≦ 10T _{0 in} this case is 0.5 mm ≦ L _p ≦ 1 mm.

The thickness Tp of the end face of the inclined portion 22 was 40 μm. Since the thickness T ₀ of the positive and negative terminals of _{0.1mm, 10μm ≦ Tp ≦ T 0} /2 in this case is 10μm ≦ Tp ≦ 50μm (0.05mm) .

  A method for measuring the thickness Tp of the end face of the inclined portion 22 is as follows.

  The end face thickness Tp was measured by observing the end face part of the inclined part 22 with a microscope.

  Furthermore, the ultra micro hardness of the inclined part 22 and the non-inclined part 23 was measured using the dynamic ultra micro hardness meter DUH-201S manufactured by Shimadzu Corporation under the test conditions shown below.

Test mode: Indenter push-in mode Test load: 50mN
Load speed: 1.323898 mN / sec
Holding time: 15 sec
Indenter type: Triangular indenter 115 °
Formula for calculating hardness: DHT115 = 3.8854 × P / D ²
Here, DHT 115 is dynamic hardness by a triangular pan indenter with a recliner angle of 115 °, P is a test load (mN), and D is an indentation depth (μm).

  As a result of the above test, the ultrafine hardness (dynamic hardness DHT115) was 51 in the inclined portion 22 and 25 in the non-inclined portion 23. Therefore, the ultra-micro hardness of the inclined portion 22 was 2.0 times that of the non-inclined portion 23.

<Production of electrode group>
First, a paste prepared by mixing 89 parts by weight of LiCoO ₂ powder as an active material, 8 parts by weight of graphite powder as a conductive filler and 3 parts by weight of polyvinylidene fluoride (PVdF) resin as a binder into 25 parts by weight of N-methylpyrrolidone. Was prepared. This paste was applied to both sides of an aluminum foil having an outer dimension of 50 mm × 370 mm and a thickness of 0.2 mm as a current collector so that an edge portion of 50 mm × 70 mm remained as an uncoated portion on one side, and after drying, The positive electrode was produced by welding the positive electrode terminal to the coated portion.

  Next, after the mesophase pitch-based carbon fiber was pulverized, 100 parts by weight of the heat-treated carbon fiber powder was mixed with an aqueous solution containing 2 parts by weight of carboxymethylcellulose and styrene-butadiene crosslinked rubber latex particles to prepare a paste. This paste was applied to both sides of a copper foil having an outer dimension of 51.5 mm × 380 mm and a thickness of 0.15 mm as a current collector so that an edge portion of 51.5 mm × 60 mm remained as an uncoated part on one side, After drying, a negative electrode was produced by welding the negative electrode terminal to the uncoated portion.

Next, after placing a polyethylene microporous film of 53 mm × 450 mm between the positive and negative electrodes and on the positive electrode side, it was wound in a spiral shape so that the outermost peripheral surface was covered with the copper foil of the negative electrode by a winding machine. A cylindrical product was prepared. Subsequently, this cylindrical object is subjected to pressure molding at room temperature under a pressure of 10 to 30 kg / cm ² , whereby a flat electrode group having a thickness of about 3 mm having the above-described positive and negative terminals 16 and 17 shown in FIG. Was made.

<Preparation of non-aqueous electrolyte>
LiPF ₆ as an electrolyte is dissolved in a non-aqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a volume ratio of 1: 1 so as to have a concentration of 1 mol / L. Was prepared.

<Manufacture of thin lithium-ion secondary batteries>
The obtained flat electrode group 8 was accommodated in the cup portion 2 of the film container 1 so that the positive and negative electrode terminals 16 and 17 extended from the edge portion 3c to the outside. Subsequently, the lid 4 of the film container 1 is bent 180 °, the lid 4 and the edges 3a to 3c are overlapped, and the two edges 3b and 3c are pressurized with a pressure of 4.0 kgf / cm ^2. However, heat fusion was performed at a temperature of 70 ° C. added to the melting point of the acid-modified LLDPE. At this time, the first resin film made of the acid-modified LLDPE of the insulating films 18a and 18b is formed on both surfaces of the positive and negative terminals 16 and 17, respectively, at the edge 3c from which the positive and negative terminals 16 and 17 are extended and the lid 4. While heat-sealing, the first resin films of the insulating films 18a and 18b were heat-sealed in the region excluding the positive and negative terminals 16 and 17. Moreover, the polyethylene film of the film container 1 was heat-sealed in the edge part 3b and the cover body 4. FIG. Thereafter, the nonaqueous electrolytic solution was injected into the cup portion 2 through the gap between the non-thermally bonded edge portion 3a and the lid body 4, and the electrode group 8 accommodated therein was impregnated with the nonaqueous electrolytic solution. . Subsequently, the non-heat-sealed portion is heat-sealed to seal the flat electrode group 8 in an airtight manner, and then the heat-sealed portions 21 ₁ and 21 ₂ are cut so as to remain 2.5 mm wide. The 1000 flat-type (thin) lithium ion secondary batteries having the structure shown in FIGS. 1 to 7 described above, having an external dimension excluding positive and negative terminals of 35 mm × 60 mm and a capacity of 300 mAh are obtained. Manufactured.

(Examples 2-3)
A flat lithium ion secondary battery (each, 1000 in total) was produced by the same method as in Example 1 except that the type of insulating resin film was changed as shown in Table 1 below.

(Examples 4 to 5)
After producing the film container 1 by the same method as in Example 1, when storing the flat electrode group 8 in the cup part 2, the part corresponding to the edge part 3c of both surfaces of the positive and negative terminals 16 and 17 An insulating film having the structure shown in Table 1 below was heat-sealed. Thereafter, a flat lithium ion secondary battery having the structure shown in FIGS. 1 to 7 and having an outer dimension of 35 mm × 60 mm and a capacity of 300 mAh, excluding the positive and negative terminals, is obtained in the same manner as in Example 1. A total of 1000) was manufactured.

(Example 6)
A strip-shaped aluminum positive electrode terminal and negative electrode terminal having a thickness T ₀ of 0.2 mm and a width L of 4 mm were prepared. About each, it crush-molded with the press in the location located in a heat-fusion part among the both end surfaces of a longitudinal direction side. The length Lp of the inclined portion was 2.0 mm. Since the thickness T ₀ of the positive and negative electrode terminals is 0.2 mm, 5T ₀ ≦ L _p ≦ 10T _{0 in} this case is 1.0 mm ≦ L _p ≦ 2.0 mm.

Further, the thickness of the end face of the inclined portion 22 was 20 μm. Since the thickness T ₀ of the positive and negative terminals of _{0.2mm, 10μm ≦ Tp ≦ T 0} /2 in this case is 10μm ≦ Tp ≦ 100μm (0.1mm) .

  Furthermore, the ultrafine hardness (dynamic hardness DHT115) was 50 in the inclined portion 22 and 25 in the non-inclined portion 23. Therefore, the ultra-micro hardness of the inclined portion 22 was 2.0 times that of the non-inclined portion 23.

  Except for using the positive and negative electrode terminals, flat lithium ion secondary batteries (each 1000 in total) were produced in the same manner as in Example 1.

(Example 7)
A strip-shaped aluminum positive electrode terminal and negative electrode terminal having a thickness T ₀ of 0.08 mm and a width L of 4 mm were prepared. About each, it crush-molded with the press in the location located in a heat-fusion part among the both end surfaces of a longitudinal direction side. The length Lp of the inclined portion was 0.4 mm. Since the thickness T ₀ of the positive and negative electrode terminals is 0.08 mm, 5T ₀ ≦ L _p ≦ 10T _{0 in} this case is 0.4 mm ≦ L _p ≦ 0.8 mm.

Further, the thickness of the end face of the inclined portion 22 was 40 μm. Since the thickness T ₀ of the positive and negative terminals of _{0.08mm, 10μm ≦ Tp ≦ T 0} /2 in this case is 10μm ≦ Tp ≦ 40μm (0.04mm) .

  Furthermore, the ultrafine hardness (dynamic hardness DHT115) was 51 at the inclined portion 22 and 26 at the non-inclined portion 23. Therefore, the ultra-micro hardness of the inclined portion 22 was 2.0 times that of the non-inclined portion 23.

  Except for using the positive and negative electrode terminals, flat lithium ion secondary batteries (each 1000 in total) were produced in the same manner as in Example 1.

(Example 8)
A strip-shaped aluminum alloy positive electrode terminal and negative electrode terminal having a thickness T ₀ of 0.1 mm and a width L of 4 mm were prepared. Aluminum alloy is composed of Al 96 wt%, Mg 2.5 wt%, Si 0.25 wt% or less, Fe 0.40 wt% or less, Cu 0.10 wt% or less, Mn 0.10 wt% or less, Zn 0.10 wt% or less. 5052 material. About each, it crush-molded with the press in the location located in a heat-fusion part among the both end surfaces of a longitudinal direction side. The length Lp of the inclined portion and the thickness of the end face were set to the same values as in Example 1.

  The ultrafine hardness (dynamic hardness DHT115) was 55 at the inclined portion 22 and 25 at the non-inclined portion 23. Therefore, the ultra-micro hardness of the inclined portion 22 was 2.2 times that of the non-inclined portion 23.

(Comparative Examples 1-5)
A flat type lithium ion secondary battery (each 1000 in total) was manufactured in the same manner as in the example except that positive and negative terminals that were not subjected to end crushing were used instead of the end crushing formed lead used in the example.

For each of the obtained batteries, the number of internal short-circuit defects in 1000 manufactured was measured, and the results are shown in Table 1. In addition, the production failure rate (%) in which defects such as chipping, warping or bending are generated in the positive electrode terminal or the negative electrode terminal when 1000 batteries are manufactured is also shown in Table 1 below. Note that the manufactured 1000 pieces do not include those determined to be defective.

  As is clear from Table 1, the batteries of Examples 1 to 8 in which the ultrafine hardness of the inclined portion is 1.5 times or more and 3 times or less of the ultrafine hardness of the non-inclined portion are the number of occurrences of short-circuiting of the positive and negative electrodes. It can be seen that (out of 1,000) is zero, and there is no manufacturing defect rate, and it has high reliability.

  On the other hand, in Comparative Examples 1 to 5 having positive and negative terminals that have no inclined portion and uniform ultra-micro hardness, no matter what kind of insulating film is used, the positive and negative electrodes are short-circuited and defective in production. occured.

  As described above in detail, according to the present invention, it is possible to provide a flat battery that prevents a short circuit failure between positive and negative electrodes and that has excellent lead seal reliability, and is particularly suitable for a secondary vehicle mounted on a hybrid vehicle or an electric vehicle. The battery is suitable as a secondary battery for power storage used for power leveling.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The perspective view which shows the flat battery which concerns on embodiment of this invention. Sectional drawing which follows II-II of the flat battery of FIG. The disassembled perspective view of the flat battery of FIG. The schematic diagram which shows the positional relationship of the positive / negative electrode terminal and heat sealing | fusion part in the flat battery of FIG. Sectional drawing which follows the VV line | wire of the flat battery of FIG. The expanded sectional view of the positive / negative terminal of FIG. Sectional drawing of the positive / negative electrode terminal in the location shown by the A section of FIG. The top view which shows the state before sealing of the flat battery which concerns on another embodiment of this invention. 2 is an optical micrograph of positive and negative electrode terminals used in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Film container, 2 ... Rectangular cup part, 3a-3c ... Edge part, 4 ... Cover body, 5 ... Thermoplastic resin film, 6 ... Aluminum foil, 7 ... Organic resin film which has rigidity, 8 ... Flat shape 11 ... positive electrode, 12 ... separator, 15 ... negative electrode, 16 ... positive electrode terminal, 17 ... negative electrode terminal, 18a, 18b, 24, 25 ... insulating film, 19 ... first resin film, 20 ... second Resin film, 21 _{1 to} 21 ₃ ... heat-sealed part, 22 ... inclined part, 23 ... non-inclined part.

Claims (5)

A film container having a heat-sealed portion at least at a part of the periphery;
A flat electrode group that is housed in the container and includes a positive electrode and a negative electrode;
A positive electrode terminal electrically connected to the positive electrode and drawn from the container through the thermal fusion part;
A negative electrode terminal electrically connected to the negative electrode and drawn out from the container through the thermal fusion part,
Each of the positive electrode terminal and the negative electrode terminal has an inclined portion whose thickness decreases toward an end surface at a portion located in the heat-sealed portion, and the ultrafine hardness of the inclined portion is higher than that of the non-inclined portion. A flat battery having a microhardness of 1.5 times or more and 3 times or less. The inclined section, said the length Lp is L _p ≦ 10T _0, and the thickness Tp of the end surface is _{Tp ≦ T 0/2 (T} 0 is the thickness of the positive electrode terminal or the negative terminal) The flat battery according to claim 1.   3. The flat battery according to claim 1, wherein the inclined portion is formed by crushing molding using a press or a roll. Further comprising an insulating film interposed in a portion located in the thermal fusion part of the positive electrode terminal or the negative electrode terminal,
The insulating film is laminated on the first resin film in contact with the positive electrode terminal or the negative electrode terminal, and has a low melt flow rate (MFR) as compared with the first resin film. The flat battery according to any one of claims 1 to 3, further comprising a second resin film.   The flat battery according to claim 1, wherein the positive electrode terminal and the negative electrode terminal are made of aluminum or an aluminum alloy.

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