JP5720132B2 - Resin film covering metal terminals for secondary batteries - Google Patents

Description

  The present invention relates to a metal terminal-coated resin film for a secondary battery that is excellent in shape stability and adhesiveness during heating.

  Conventional water-based batteries such as nickel-metal hydride and lead-acid batteries have a limit of about 1.2 V in terms of cell unit voltage due to restrictions on water electrolysis voltage. Recently, however, miniaturization of portable devices and effective utilization of natural power generation energy are required, and the need for lithium ion batteries with higher voltage and high energy density is increasing. Conventionally, metal cans have been used as exterior materials for such lithium-ion batteries, but resin films are laminated on aluminum foil that can be used at low cost to meet the demands for thinner and diversified products. Laminated wrapping materials in the form of bags have been used.

  The laminated packaging material for secondary batteries (hereinafter referred to as packaging material) is a laminate of an aluminum foil and a resin as shown in FIG. 1. Generally, a polyolefin resin layer 11, an inner layer side adhesive layer 12, It has the structure of the chemical conversion treatment layer 13, the aluminum foil layer 14, the chemical conversion treatment layer 13, the outer layer side adhesive bond layer 15, and the outer layer 16 (nylon, PET, etc.).

  In order to supply electric power from a lithium ion battery composed of such a packaging material, an electrode terminal called a tab is required. As shown in FIG. 2, the tab is composed of a metal terminal 23 (lead) and a metal terminal covering resin film 21 (sealant). Aluminum is used for the lead of the positive electrode and is often subjected to a corrosion prevention surface treatment 22. Nickel or copper is used for the negative electrode. Since the purpose of the sealant is to obtain adhesion between the lead and the packaging material, the following two characteristics are mainly required. One is to have adhesion between both metal and polyolefin resin. For this, a method of introducing a polar group by acid-modifying polypropylene or polyethylene, which is a polyolefin resin used for a sealant, is generally used. Another required characteristic is shape stability during heating. Specifically, the deformation of the sealant is suppressed when the lead and the sealant are thermally bonded. As described in Patent Documents 1 and 2, conventional techniques for these required characteristics are provided with a method of increasing the heat resistance by providing a resin crosslinking step, and using a polyester resin for the heat-resistant layer to increase the shape stability. A method has been proposed. However, in applications of large batteries such as in-vehicle and power generation, further improvement in dimensional accuracy of the sealant and improvement in adhesion between the lead and the sealant are required.

Japanese Patent No. 3114174 JP 2008-230620 A

  Therefore, the present invention has been made in view of the above circumstances, and does not require the addition of a step such as cross-linking, improves the shape stability during thermal bonding between the lead and the sealant, and can secure adhesion. It aims at provision of the metal terminal covering resin film for secondary batteries.

The invention according to claim 1 is a laminated metal terminal covering resin film for a secondary battery covering a metal terminal connected to a positive electrode or a negative electrode of a secondary battery, wherein the metal terminal covering resin film for a secondary battery is And an adhesive layer in contact with the metal terminal, and a single heat-resistant layer constituting the outermost layer, wherein the entire layer of the metal terminal covering resin film for the secondary battery is made of polypropylene resin, and the adhesive layer and Each of the heat-resistant layers is made of a resin having a melt flow rate of 3 g / 10 min or more and 7 g / 10 min or less, and the heat-resistant layer is made of a propylene homopolymer having a melting point of 150 to 165 ° C. It is a metal terminal covering resin film for secondary batteries. By setting the melt flow rate (MFR) within this range, deformation of the sealant during heating can be reduced.

Moreover , according to the structure of Claim 1, thermal adhesiveness with the inner layer of a packaging material is securable. In addition, even when the structure of the metal terminal covering resin film for secondary batteries of the present invention (hereinafter sometimes simply referred to as a resin film) is composed of a plurality of layers, the same type is used to ensure adhesion between layers. It is preferable that the resin (polyolefin resin) is used. Moreover, in the case of the resin film which laminated | stacked the same kind of resin, it becomes possible to make a film simply by a coextrusion molding method etc.

The invention according to claim 2 is the metal terminal-coated resin film for a secondary battery according to claim 1, wherein the adhesive layer and the heat-resistant layer have a melting point difference of 5 ° C. or more. According to this configuration, deformation of the resin film can be reduced during the thermal bonding between the resin film of the present invention and the lead.

The invention described in claim 3 is characterized in that the metal terminal covering resin film for a secondary battery is in contact with a packaging material for a secondary battery having a polyolefin-based resin on at least one outermost layer. It is a metal terminal covering resin film for secondary batteries in any one of -3. According to this structure, the adhesiveness of a packaging material and the resin film of this invention becomes favorable.

  According to the present invention, it is not necessary to add a step such as cross-linking, and it is possible to prevent a decrease in adhesive strength due to the lamination of different materials, and the shape at the time of thermal bonding between the lead and the resin film of the present invention. It is possible to provide a metal terminal-coated resin film for a secondary battery that can be expected to improve the stability and peel strength of the secondary battery.

It is sectional drawing of an example of the laminated packaging material for lithium ion batteries. It is sectional drawing of an example of a general tab. It is sectional drawing which shows embodiment of the sealant of this invention. It is sectional drawing of an example of a tab.

  Hereinafter, the present invention will be described in detail. As described above, the resin film (sealant) of the present invention uses an adhesive resin that has low fluidity at high temperatures and maintains adhesion to both the metal and the polyolefin resin in order to maintain shape stability during heating. Is good. In order to further improve the insulation and shape stability, it is preferable that a resin having a higher melting point than the adhesive resin is laminated with the adhesive layer as a heat resistant layer. FIG. 3 is a cross-sectional view showing an embodiment of the sealant of the present invention having a structure in which a heat-resistant layer and an adhesive layer are laminated. The adhesive layer 31 and the heat-resistant layer 32 are laminated.

<Adhesive layer>
The adhesive layer 31 is preferably a resin excellent in adhesion between both the lead and the polyolefin resin. For example, an acid-modified polyolefin resin obtained by graft-modifying maleic anhydride or the like on a polyolefin resin is preferable. The thickness of the adhesive layer 31 is preferably about 10 to 200 μm per layer, and more preferably 20 to 150 μm in order to obtain good adhesion between the metal terminal and the packaging material. The higher the melting point of the resin, the more likely it is to impair the productivity. When the melting point of the resin is low, there is a possibility of lowering the reliability. Therefore, when considering the melting point of the adhesive layer generally used in packaging materials, the temperature is about 120 to 150 ° C. preferable. Moreover, in order to improve the shape stability at the time of a heating, the one where MFR is low is preferable. Specifically, 7 g / 10 min or less is preferable.
The MFR referred to in the present invention is a value measured at ASTM D1238, 190 ° C., 2.16 kg.

<Heat resistant layer>
The heat resistant layer 32 is preferably a polyolefin resin in view of the packaging material and the adhesiveness with the adhesive layer 31. Further, in order to improve the stability of the shape at the time of thermal bonding between the lead and the sealant, a melting point higher than the bonding temperature is preferable. Specifically, a resin (homo, block) having a melting point of about 150 to 165 ° C. is used. preferable. Moreover, in order to improve the shape stability at the time of a heating, the one where MFR is low is preferable, However For the reason mentioned above, 7 g / 10min or less is preferable.

  For the adhesion between the sealant and the lead created as described above, the adhesive layer is melted by heating, and the sealant and the lead are simultaneously adhered by pressurization and thermally bonded. In order to obtain sufficient peel strength, the heating temperature needs to be higher than the melting point temperature of the adhesive layer. Further, when there is a heat-resistant layer, the heating temperature is preferably not higher than the melting point temperature of the heat-resistant layer, and even when there is no heat-resistant layer, it is preferably not higher than the melting point temperature of the resin constituting the outer layer of the packaging material. Specifically, about 140 to 170 ° C. is appropriate. The heating and pressurizing time needs to be determined in consideration of the peel strength and productivity, and is preferably about 1 s to 10 s.

  FIG. 4 is a cross-sectional view of an example of a tab. The lead 43 is covered with the sealant of the present invention in which the adhesive layer 41 and the heat-resistant layer 42 are alternately laminated.

  Examples of the present invention are shown below, but the present invention is not limited to the following examples.

  A film having a three-layer structure in which the heat-resistant layer 32 is sandwiched between the adhesive layers 31 as shown in FIG. The heat-resistant layer 32 was made of homopolymer polypropylene. The melting point is 160 ° C. and the MFR is 3 g / 10 min. The adhesive layer 31 used was a resin obtained by graft-modifying maleic anhydride on polypropylene. The melting point is 140 ° C., and the MFR is 3 g / 10 min similarly to the heat-resistant layer 32. The thickness of the heat-resistant layer 32 using the above resin was 40 μm, the thickness of each adhesive layer 31 was 30 μm, and a sealant with a total thickness of 100 μm was formed by extrusion molding. Each sealant was cut into 9 mm × 20 mm, the lead was sandwiched between the two sealants, and the film and the lead were thermally bonded at 190 ° C. for 3 seconds while applying pressure to produce a tab. The lead was soft aluminum, and the dimensions were 5 mm × 30 mm and the thickness was 100 μm.

Comparative Example 1

  Similar to Example 1, a film having a three-layer structure in which a heat-resistant layer was sandwiched between adhesive layers was prepared. Polyethylene terephthalate (PET) was used for the heat resistant layer. The melting point was 264 ° C. and the thickness was 25 μm. For the adhesive layer, a resin obtained by graft-modifying maleic anhydride on polypropylene was used. The melting point is 140 ° C., and the MFR is 3 g / 10 min as in Example 1. The adhesive layer was sand-laminated to the PET resin, the thickness of each adhesive layer was 30 μm, and a film having a total thickness of 85 μm was prepared. Moreover, the tab was created like Example 1 using the created film.

Comparative Example 2

  A sealant and a tab were prepared in the same manner as in Example 1 except that the MFR of the heat-resistant layer and the adhesive layer was 8 g / 10 min.

<Evaluation 1: Evaluation of shape stability>
The dimensional variation of the sealant portion of the tab created above was measured, and ± 300 μm or less was regarded as a conforming product.

<Evaluation 2: Evaluation of peel strength>
The tab created above was sandwiched between packaging materials, heated and pressurized, and after thermal bonding, the packaging materials were pulled in the 180 ° direction to measure peel strength.

<Evaluation results>
Table 1 shows the evaluation results. Regarding shape stability (size fluctuation), Example 1 and Comparative Example 1 were conforming products, but Comparative Example 2 was non-conforming product. Since the difference between Example 1 and Comparative Example 2 is only the MFR of the resin, it was confirmed that selection of the optimum MFR is important. Moreover, in the shape stability of the comparative example 1, since resin (PET) with high melting | fusing point was used as a heat resistant layer, it is thought that it was hard to receive the deformation | transformation at the time of a heating. Only the comparative example 1 was low in peel strength. This is considered to be because the compatibility of the resin between the heat-resistant layer and the adhesive layer is low, and it was thus confirmed that the sealant needs to be laminated with the same kind of resin of all-layer polyolefin type. From the above, it was possible to achieve both the stability of the shape during heating and the securing of the peel strength in the configuration of Example 1, and thus the effectiveness of the present invention was confirmed.

DESCRIPTION OF SYMBOLS 11 Polyolefin resin layer, 12 Inner layer side adhesive layer, 13 Chemical conversion treatment layer, 14 Aluminum foil layer, 15 Outer layer side adhesive layer, 16 Outer layer (nylon, PET, etc.), 21 Sealant, 22 Chemical conversion treatment layer, 23 Lead, 31 Adhesive layer, 32 heat-resistant layer, 41 adhesive layer, 42 heat-resistant layer, 43 lead.

Claims (3)

In the laminated metal terminal covering resin film for the secondary battery covering the metal terminal connected to the positive electrode or the negative electrode of the secondary battery,
The metal terminal covering resin film for a secondary battery has an adhesive layer in contact with the metal terminal, and one heat-resistant layer constituting the outermost layer,
All layers of the metal terminal covering resin film for the secondary battery are composed of polypropylene resin,
Each of the adhesive layer and the heat-resistant layer is composed of a resin having a melt flow rate of 3 g / 10 min to 7 g / 10 min .
The said heat-resistant layer consists of a homopolymer of propylene which has 150-165 degreeC of melting | fusing point , The metal terminal covering resin film for secondary batteries characterized by the above-mentioned.   2. The metal terminal-coated resin film for a secondary battery according to claim 1, wherein the adhesive layer and the heat-resistant layer have a melting point difference of 5 ° C. or more. The secondary battery metal terminal-coated resin film is in contact with a secondary battery packaging material having a polyolefin-based resin on at least one outermost layer thereof . Metal terminal covering resin film.

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