JP5449800B2 - Laminated battery - Google Patents

Description

  The present invention relates to a laminated battery, and in particular, even when the side seal part is bent so as to be along the cup-shaped molded body side, the side seal part is hardly broken, and the sealing reliability of the side seal part is improved. The present invention relates to an improved laminated battery.

  It has high energy density as a driving power source for portable electronic devices such as today's mobile phones, portable personal computers, portable music players, and also as a power source for hybrid electric vehicles (HEV) and electric vehicles (EV). However, non-aqueous secondary batteries typified by high-capacity lithium ion secondary batteries are widely used.

  These non-aqueous secondary batteries generally include a positive electrode in which a positive electrode mixture containing a positive electrode active material that occludes and releases lithium ions is applied to both surfaces of a positive electrode core made of an elongated sheet-like aluminum foil, and an elongated sheet A negative electrode core material (current collector) made of copper foil or the like, and a negative electrode in which a negative electrode mixture containing a negative electrode active material that occludes and releases lithium ions is applied, and is microporous between the positive electrode and the negative electrode A separator made of a conductive polyethylene film or the like is arranged, and a positive electrode and a negative electrode are insulated from each other by a separator and wound into a columnar or elliptical shape to form a wound electrode body. Are formed by connecting the positive electrode tab and the negative electrode tab to predetermined portions of the positive electrode and the negative electrode, respectively, and covering the outside with an exterior.

  As this outer package, that is, a battery package, a metal outer can is mainly used to give strength to the battery. However, it is replaced with an outer can for the purpose of reducing the weight or increasing the battery capacity per unit volume. A laminate battery in which a metal-resin laminate film is used as a packaging material and a wound electrode body is laminated and packaged is also known. In such a laminated battery, the use of the laminated film as a battery package increases the complexity of the manufacturing process, solves problems such as strength as an exterior, reliability of sealing, and increases battery capacity. In order to achieve higher performance, improvements are being made every day.

  For example, in Patent Document 1 below, the thickness of the side sealing portion of the laminate exterior is made thinner than the thickness of the top sealing portion, so that the cross-sectional area of the sealant layer serving as a moisture permeation path is reduced. Thus, an invention of a laminated battery in which moisture intrusion is suppressed is disclosed. According to the invention of this laminated battery, it is said that battery swelling can be suppressed, and furthermore, the width of the side sealing portion can be made narrower than that of the conventional one, so that high capacity can be achieved. Yes.

JP 2004-303589 A JP 2005-285526 A

  Such a laminate battery is manufactured by folding and laminating a laminate material in a state in which a wound electrode body is housed in a cup-molded metal-resin laminate material, and sealing both sides by heat sealing. However, when the side seal part is bent to the cup molding side after that, the bottom of the structure is weak in bending resistance and the tensile stress to the laminate material is the strongest, so if the battery vibrates or the side seal part When force is applied, the laminated metal layer has a fracture or a tensile fracture (so-called crack) due to fatigue at the bottom, and there is a problem that the reliability of sealing is lowered.

  On the other hand, in Patent Document 2 described above, even if stress is applied by cracking the folded portion of the sealing portion on both sides of the laminated battery by reinforcing the folded portion with resin or fixing the folded portion, a crack is generated in the folded portion. Thus, there has been disclosed an invention of a laminated battery in which the appearance defect is suppressed, the sealing structure is hardly broken, and the reliability of the laminated battery is improved.

  However, if the folded part of the folded part of the sealing part on both sides of the laminated battery is reinforced with resin or the folded part is fixed, the thickness of the sealing part on both sides increases, so that the battery size becomes constant. If this is done, the battery capacity will decrease, and if the battery capacity is kept constant, the battery size will increase.

  The present invention has been developed to solve the problems of the conventional laminated battery as described above. That is, the present invention reduces the battery capacity or increases the battery size by reviewing the structure of the side sealing portion even when the side seal portion is bent along the cup-shaped molded body side. An object of the present invention is to provide a laminated battery in which the side seal part is hardly broken and the sealing reliability of the side seal part is improved.

In order to achieve the above object, the laminated battery of the present invention comprises an electrode body having an electrode lead tab at one end inside a cup-shaped molded body obtained by folding a packaging material made of a metal-resin laminate material. Is inserted so as to be exposed to the outside from the top portion of the cup-shaped molded body, side seal portions are provided on both sides of the cup-shaped molded body, and a top seal portion is disposed on the top portion of the cup-shaped molded body. However, in each of the laminated batteries formed by heat sealing and bent so that at least one of the side seal portions on both sides is along the cup-shaped formed body side, the bent side seal portion is when the entire length of the side seal portions was set to L, 87.1~ thickness of a region a of length 0.03L~0.5L the thickness of the other portion Is 3.9% the region A, the distance from the position corresponding to the bottom of the cup-like shaped body to a lower end of the region A and D1, the upper end of the side seal part from the upper end of the region A When the distance to the corresponding position is D2, it is formed at a position that satisfies the condition of D1 / D2 ≦ 0.800 .

In the laminated battery of the present invention, in the side seal portion, the region from the upper end of the region A to the position corresponding to the upper end of the side seal portion (hereinafter referred to as “region B”) and the bottom of the cup-shaped molded body. There are three regions from the corresponding position to the lower end of region A (hereinafter referred to as “region C”), and the thicknesses of the side seal portions of region B and region C are constant, and region A Is 87.1 to 93.9% of the thickness of the region B and the region C. Thus, if the thickness of the region A is made thinner than the thickness of the other portions, the amount of resin existing between the metal layers of the laminate material is reduced in the region A, so that the buffering action is prevented against deformation at the time of bending. Since it decreases, durability against bending increases. For this reason, the region A is more resistant to bending than the regions B and C, and the length D2 of the region B is longer than the length D1 of the region C. Since the force applied to the part is distributed to the region B, it is difficult to apply an external force to the region C. Therefore, according to the laminate battery of the present invention, cracks at the bottom of the side seal are hardly generated, and a laminate battery with improved reliability can be obtained.

  In addition, the thickness of the side seal part can be easily performed by changing the width between the heat heads for each region by changing the shape of the heat head used for heat sealing, and further, the pressure of the upper and lower heat heads It can also be performed by adjusting the above. The length of the region A needs to be in the range of 0.03L to 0.5L, where L is the total length of the side seal portion. If the length of the region A is less than 0.03L or more than 0.5L, the crack formation rate in the region C increases rapidly, which is not preferable.

In addition, a relationship of D1 / D2 ≦ 0.800 needs to be established between the length D2 of the region B and the length D1 of the region C. If the relationship between the length D2 of the region B and the length D1 of the region C is D1 / D2 ≧ 1, it is not preferable because the crack formation rate in the region C increases rapidly. In the laminated battery of the present invention, the region C is not necessarily provided, and D1 = 0 may be used. Further, the electrode body may be a flat wound electrode body or a laminated electrode body, and may be a secondary battery using an aqueous electrolyte such as a nickel-hydrogen secondary battery.

  In the laminated battery of the present invention, it is preferable that the values of D1 and D2 satisfy the condition of D1 / D2 ≦ 0.3.

  According to the laminated battery of the present invention, when the values of D1 and D2 satisfy the condition of D1 / D2 ≦ 0.3, the cracks are less likely to occur at the bottom.

  Moreover, in the laminated battery of this invention, it is preferable that the said electrode body is an electrode body for nonaqueous electrolyte secondary batteries.

  Since the nonaqueous electrolyte secondary battery has a large capacity per unit volume and unit weight, the effect of the present invention is greatly exhibited particularly when a small laminate battery is used.

1A is a plan view of a laminated battery according to each example and comparative example of the present invention, FIG. 1B is a bottom view of FIG. 1A, and FIG. 1C is a bottom view of the laminated battery in actual use.

  Hereinafter, the form for implementing this invention is demonstrated in detail using an Example and a comparative example. However, the following examples show an example of a laminated battery for embodying the technical idea of the present invention, and are not intended to limit the present invention to this example. The present invention can be equally applied to various modifications without departing from the technical idea shown in the claims.

Initially, the specific manufacturing method of the nonaqueous electrolyte secondary battery as a laminated battery used in common with Examples 1-13 and Comparative Examples 1-8 is demonstrated.
[Preparation of positive electrode plate]
Lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, carbon black (Denka Black HS-100 manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive agent, and polyvinylidene fluoride (PVdF) powder as a binder, 95: 2 After mixing uniformly at a ratio of 5: 2.5 (mass ratio), the mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode active material slurry. This positive electrode active material slurry was applied to both surfaces of a positive electrode current collector made of aluminum foil with a thickness of 12 μm by a doctor blade method so as to have a uniform coating amount of 360 g / m ^2, and then passed through a dryer to pass NMP. By removing by drying, a positive electrode active material layer was formed on both surfaces of the positive electrode current collector. Then, this positive electrode plate was rolled with a roll press so that the filling density was 3.70 g / cm ³ , cut into a predetermined size, and common to Examples 1 to 13 and Comparative Examples 1 to 8. A positive electrode plate to be used was prepared.

[Production of negative electrode plate]
Artificial graphite (average particle diameter d50 = 0.335 nm) as a negative electrode active material, carbon nanofibers (VGCF manufactured by Showa Denko KK) as a conductive agent, carboxymethylcellulose (CMC) as a thickener, and as a binder Styrene-butadiene rubber (SBR) was uniformly mixed at a ratio of 95: 3: 1: 1 (mass ratio), and then dispersed in water to prepare a negative electrode active material slurry. This negative electrode active material slurry was applied on both sides of a negative electrode current collector of copper foil having a thickness of 8 μm by a doctor blade method so as to have a uniform coating amount of 160 g / m ^2, and then passed through a dryer to pass water. By removing it by drying, a negative electrode active material layer was formed on both surfaces of the negative electrode current collector. Then, this negative electrode plate was rolled with a roll press so that the packing density was 1.60 g / cm ³ , cut into a predetermined size, and common to Examples 1 to 13 and Comparative Examples 1 to 8. A negative electrode plate to be used was prepared. The charge capacity ratio between the positive electrode and the negative electrode was adjusted so that the negative electrode charge capacity / the positive electrode charge capacity = 1.1 when the battery voltage during charging was 4.2 V.

[Production of wound electrode body]
A current collecting tab is welded to each of the positive electrode plate and the negative electrode plate produced as described above, and then wound with a winder with a polyethylene microporous membrane separator (12 μm) in between. A flat wound electrode body used in common in Examples 1 to 13 and Comparative Examples 1 to 8 was manufactured by attaching and pressing an insulating winding stop tape to the end portion.

[Preparation of non-aqueous electrolyte]
As the non-aqueous electrolyte, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed at 40:20:40 (1 atm, volume ratio at 25 ° C.). A nonaqueous electrolyte solution commonly used in Examples 1 to 13 and Comparative Examples 1 to 8 is prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt in a nonaqueous solvent so as to be 1 mol / L. Was prepared.

[Laminate]
As a laminate material commonly used in Examples 1 to 13 and Comparative Examples 1 to 8, a thickness of 15 μm is formed on one surface of the metal layer having a thickness of 35 μm made of aluminum (the surface on the outside of the laminated battery). A nylon layer having a thickness of 30 μm was disposed on the other surface of the metal layer (the surface on the inner side of the laminated battery). The metal layer and the nylon layer are bonded by a dry laminate adhesive layer having a thickness of 5 μm, and the metal layer and the polypropylene layer are bonded by a carboxylic acid-modified polypropylene layer having a thickness of 5 μm in which a carboxyl group is added to polypropylene. The total thickness of the laminate material is 90 μm.

[Production of battery]
The above-mentioned laminate material was previously cup-molded so that a flat wound electrode body could be inserted. Next, after the wound electrode body obtained as described above is accommodated in the cup-shaped laminate, an L-shaped heat head is used as in the case of the invention disclosed in Patent Document 1. The first side seal portion 15a and the top seal portion 16 were formed by heat-sealing one side surface and the side where the positive electrode lead tab 11 and the negative electrode lead tab 12 are disposed. Next, after injecting 5 ml of the non-aqueous electrolyte from the other side surface and performing an impregnation treatment, the second side seal portion 15b is removed by heat-sealing the other side surface using a bar-shaped heat head. Formed and sealed. In addition, the L-shaped heat head and the bar-shaped heat head used here have convex portions formed so that the thickness of the heat seal portion corresponding to the region A shown below is reduced. Was used. Thereafter, charging and discharging were performed, and square laminated batteries having a thickness of 5 mm, a width of 45 mm, and a height of 62 mm used in Examples 1 to 13 and Comparative Examples 1 to 8 were produced. The design capacity of each obtained nonaqueous electrolyte secondary battery is 1500 mAh.

  The first and second side seal portions 15a and 15b are formed between the rectangular region A having a predetermined thickness X and the upper end of the region A and the upper end of the side seal portion (the current collecting tab side of the laminated battery). A region B having a predetermined thickness Y and a region C having a predetermined thickness Y between the lower end of the region A and the lower end of the side seal portion (the bottom side of the laminated battery), so that X <Y. Has been. In addition, the seal thickness control of the side seal part was performed by changing the position, that is, the width between the heat heads. The total length L of the side seal from the lower end of the side seal portion to the lower end of the top seal portion was L = 58.0 mm.

As shown in FIG. 1A and FIG. 1B, the laminated battery 10 used in each of the obtained Examples and Comparative Examples has a flat wound electrode body 13 having a positive electrode lead tab 11 and a negative electrode lead tab 12 made of a laminate material. The first and second side seal portions 15a and 15b are formed on both side ends, and the top seal portion 16 is formed on the upper end side. In addition, as shown in FIG. 1C, both side seal portions 15 on both sides are usually used by being bent along the cup-shaped molded body 14 side. The symbols used for convenience to indicate the size and position of each region of the side seal of the laminated battery are defined as follows.
α = seal length in region A D1 = seal length in region C D2 = seal length in region B Note that α + D1 + D2 = L holds.

[Vibration test]
250 cells of the laminated batteries of Examples 1 to 13 and Comparative Examples 1 to 8 prepared as described above were prepared and vibrated under the following conditions.
Amplitude: 2 mm
Frequency: 5Hz
Vibration time: 180 min
Subsequently, the crack formation rate was calculated by the following calculation formula, and is shown in Table 1, Table 2, and Table 3.
Crack formation rate (%)
= (Number of cells with cracks at the bottom of the laminate battery / 250) × 100

[Examples 1 to 5, Comparative Examples 1 to 4]
Table 1 shows that seal thickness X in region A is constant at 120 μm, seal thickness Y in regions B and C is constant at 130 μm, and D1 is constant at 0.1 L, and α is between 0 L and 1.0 L. That is, α = 0L (Comparative Example 1), α = 0.02L (Comparative Example 2), α = 0.03L (Example 1), α = 0.06L (Example 2), α = 0.1 L (Example 3), α = 0.3 L (Example 4), α = 0.5 L (Example 5), α = 0.6 L (Comparative Example 3), α = 1.0 L (Comparative Example) It is summarized as 4).

  From the results shown in Table 1, the following can be understood. First, it can be seen that cracks are likely to be formed at the bottom when the thickness of the side seal portion is constant over the entire thickness (Comparative Examples 1 and 4) regardless of the difference in thickness of the heat seal. In addition, when α is 0.02 L or less or 0.6 L or more, the effect of suppressing the crack formation at the bottom is hardly seen, but when α is 0.03 L or more and 0.5 L or less, the crack formation at the bottom is effectively performed. Can be suppressed. In particular, it is more preferable that α is 0.06L or more and 0.3L or less because cracks are hardly formed at the bottom.

[Examples 6-9, Comparative Examples 5-6]
Table 2 shows that α = 0.1 L constant, D1 = 0.1 L constant, and the seal thickness Y of regions B and C is constant 130 μm, and the region A seal thickness X is varied between 115 to 130 μm. That is, X = 115 μm (Example 10), X = 117 μm (Example 9), X = 119 μm (Example 8), X = 123 μm (Example 7), X = 124 μm (Example 6), 127 μm ( Comparative examples 6) and 130 μm (comparative example 5) are summarized together with the results of Example 3 (X = 121 μm).

From the results shown in Table 2, it can be seen that even when α = 0.1 L, if the value of X / Y exceeds 94%, the effect of suppressing crack formation at the bottom is not observed. In order to effectively suppress the formation of cracks bottom value is preferably 87.1 to 93.9% of the X / Y, more preferably 85-93%, even more preferably from 90 to 92%.

[Examples 10 to 13, Comparative Examples 7 to 8]
Table 3 shows that the seal length α in the region A is constant at 0.1 L, the seal thickness X in the region A is constant at 120 μm, and the seal thickness Y in the regions B and C is constant at 130 μm. 8, ie, D1 = 0L (Example 11), D1 = 0.2L (Example 12), D1 = 0.4L (Example 13), D1 = 0.6L (Comparative Example 7) D1 = 0.8L (Comparative Example 8) is summarized together with the results of Example 3 (D1 = 0.1L).

From the results of Table 3, even when α = 0.1 L and the values of X / Y are within the range of 87.1 to 93.9% , if D1 / D2 ≧ 1, the crack formation at the bottom is suppressed. It turns out that an effect is not seen. In order to effectively suppress the formation of cracks at the bottom, D1 / D2 ≦ 0.800 is preferable. From the comparison of Example 12 and Example 13, it is understood that D1 / D2 ≦ 0.3 is more preferable. .

  As described above, according to the laminated battery having the configuration of the present invention, it is possible to obtain a laminated battery in which the side seal portion is hardly broken and the sealing reliability of the side seal portion is improved.

  In addition, as a metal layer of the laminate material that can be used in the laminate battery of the present invention, not only aluminum but also aluminum alloy, stainless steel, and the like can be used, but aluminum is more preferable. As aluminum, soft aluminum and semi-hard aluminum are preferable, and the thickness is preferably in the range of 7 to 100 μm.

  In addition, as the inner layer (battery inner side) of the laminate material, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene / acrylic acid copolymer, ethylene / methacrylic acid copolymer, ethylene / ethyl acrylate copolymer, ethylene・ Methyl methacrylate copolymer, ethylene methyl acrylate copolymer, ionomer resin, ethylene-ethyl acrylate-maleic anhydride terpolymer, polyolefin, carboxylic acid modified polyethylene, carboxylic acid modified polypropylene, carboxylic acid modified ethylene -A thermoplastic resin single layer made of one kind of vinyl acetate, vinyl chloride, polystyrene or the like, or a blend of two or more kinds can be used. Carboxylic acid-modified polypropylene is particularly preferable from the viewpoints of welding strength, sealing properties, and heat resistance.

  Moreover, as the outer layer (battery outer side) of the laminate material, it is possible to use a single layer film such as a polypropylene film (OPP film), a polyester film (PET film), a nylon film (stretched film) or a multilayer film in which these are laminated. it can. The thickness of each film is preferably 20 to 40 μm for the OPP film, 6 to 25 μm for the PET film, and 15 to 25 μm for the ONY film. Of these, nylon and PET film are particularly preferable from the viewpoint of moldability.

  Moreover, as an adhesive layer for dry lamination, polyester polyol, polyether polyurethane, or the like can be generally used. However, these have the disadvantage that the resistance to electrolyte is low and the laminate strength between the aluminum foil layer and the sealant layer is lowered, so as a method other than dry lamination, a solution-type adhesive resin is applied on the aluminum foil. A heat laminating method in which the sealant layer is bonded by thermocompression bonding from above can be used. Moreover, in each said Example, although the example which manufactured the laminated battery by the two-step heat seal using the L-shaped heat head and the bar-shaped heat head was shown, only the bar-shaped heat head was used. After sealing both sides, a laminated battery may be manufactured by a three-step heat seal in which liquid is injected from the top side and finally the top side is sealed.

  DESCRIPTION OF SYMBOLS 10 ... Laminate battery 11 ... Lead tab for positive electrodes 12 ... Lead tab for negative electrodes 13 ... Winding electrode body 13 ... Electrode body 14 ... Cup-shaped molded body 15a ... 1st side seal part, 15b ... 2nd side seal part 16 ... Top seal

Claims (3)

An electrode body provided with an electrode lead tab at one end inside the cup-shaped molded body obtained by folding back a packaging material made of a metal-resin laminate, and the electrode lead tab is exposed from the top of the cup-shaped molded body to the outside. A side seal portion is formed on both sides of the cup-shaped molded body, and a top seal portion is formed on the top portion of the cup-shaped molded body by heat sealing, respectively. In the laminated battery in which at least one of the side seal portions is bent so as to be along the cup-shaped molded body side,
Side seal portion being said bending, when the entire length of the side seal portions was set to L, 87.1-93 thickness of a region A of length 0.03L~0.5L the thickness of the other portion .9% ,
In the region A, the distance from the position corresponding to the bottom of the cup-shaped molded body to the lower end of the region A is D1, and the distance from the upper end of the region A to the position corresponding to the upper end of the side seal portion A laminated battery characterized by being formed at a position satisfying the condition of D1 / D2 ≦ 0.800 when D2 .   The laminated battery according to claim 1, wherein the values of D1 and D2 satisfy a condition of D1 / D2 ≦ 0.3.   2. The laminated battery according to claim 1, wherein the electrode body is an electrode body for a non-aqueous electrolyte secondary battery.