JPH046070B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a flat battery, particularly a battery equipped with a flat power generation element using an organic electrolyte, and an exterior film thereof. Conventional configuration and its problems In order to prevent performance deterioration due to storage, flat batteries use flat power generation elements that are packaged in a liquid-tight and air-tight manner with an exterior film. In particular, in the case of flat power generating elements that use organic electrolytes, the influence of moisture in the outside air entering the battery and electrolyte leakage is significant, so the exterior components must be airtight, liquid-tight,
Particularly in consideration of electrolyte resistance, Figures 1 and 2 are
The multilayer film shown in the figure has been used so far. Figure 1 shows a heat-resistant resin film 1 that forms the surface material.
, shows a multilayer film in which an aluminum foil 2 for maintaining airtightness and an adhesive resin layer 3 that is resistant to organic electrolyte and has good thermal adhesion to the current collector metal of the positive and negative electrodes are integrated in a laminated form. . In addition, Fig. 2 shows an improved version of the exterior film shown in Fig. 1, in which another film is added between the aluminum foil 2 and the adhesive resin layer 3 in order to prevent the aluminum foil from being exposed when the flat power generating element is exteriorized. A resin film 4 is arranged. When the adhesive resin layer 3 on the innermost surface is made of polyethylene or polypropylene containing a carboxyl group that has good thermal adhesion to the current collector metal, this resin film 4 is made of a resin with a higher heat-fusion temperature than that of polyethylene or polypropylene. This prevents the aluminum foil 2 from being exposed even when the adhesive resin layer 3 melts. However, the exterior film shown in FIG. 1 had the following problems. The first is in the process of heat-sealing an exterior film around the flat power generation element in order to exteriorize it.
Pinholes are generated in the innermost adhesive resin layer, and the electrolyte reaches the aluminum foil in the exterior film through the pinholes, corroding the aluminum foil. In the exterior film shown in FIG. 2, since the resin film 4 is disposed between the adhesive resin layer 3 and the aluminum foil 2, the occurrence of pinholes as described above is suppressed. As such a resin film 4, it is necessary to use a resin having excellent moisture permeation resistance and electrolyte resistance, such as a polyethylene terephthalate film. It has no adhesive properties. In addition, welding adhesives and non-solvent adhesives that polymerize or crosslink during adhesion will peel off due to penetration of the electrolyte, so they should not be used inside this inner adhesive resin layer. I can't. For this reason,
The resin film 4 does not have sufficient adhesive strength to be bonded to the adhesive resin layer 3, and the exterior film shown in both FIG. 1 and FIG. Therefore, it is not possible to satisfy both the requirements of peeling resistance and peeling resistance. The second problem is that when thermally adhering the current collector metal and the exterior film, the current collector metal may break the inner resin layer or resin film, or penetrate through it and come into contact with the aluminum foil, causing electrolysis with dissimilar metals. It is the formation of a local battery by the action of a liquid. Due to the formation of this local battery, either the current collector or the aluminum foil is eluted or oxidized. In particular, if the aluminum foil in the outer film leaches, the organic electrolyte may evaporate from the leached part, or moisture in the outside air may enter the battery, causing gas generation and causing battery failure, or in the worst case scenario. There was a problem with the battery exploding. OBJECT OF THE INVENTION The present invention solves the above-mentioned problems of the conventional method by providing a layer of heat-resistant synthetic resin non-woven fabric inside the aluminum foil of the exterior film to prevent pinholes from forming in the internal adhesive resin layer. The purpose is to prevent the electrolyte from reaching the aluminum foil even if it occurs, and to prevent electrical contact between the aluminum foil and the current collector metal, thereby improving the discharge characteristics and storage performance of flat batteries. do. Structure of the Invention In order to achieve the above-mentioned object, the present invention provides an inner adhesive resin layer that constitutes an exterior film together with a heat-resistant resin film and an aluminum foil. It has at least a three-layer structure with a heat-resistant synthetic resin non-woven fabric placed between the resin film and the resin film on both sides is thermally fused to allow the resin to penetrate, making the non-woven fabric impermeable to electrolyte vapor in its thickness direction. It is characterized by the fact that it is maintained. According to the present invention, the heat-resistant synthetic resin nonwoven fabric can prevent the electrolyte from reaching the aluminum foil even if a pinhole is generated in the innermost resin film during heat fusion, and the electrolyte can be prevented from concentrating with the aluminum foil. It can cut off contact with electric metals. DESCRIPTION OF EXAMPLES Hereinafter, details of the present invention will be explained with reference to examples. Figure 3 is a cross-sectional view of an exterior film that covers a flat power generating element in an embodiment of the present invention, and includes a heat-resistant resin film indicated by 1 in the figure and an aluminum foil with a thickness of 9μ or more bonded to one side of the film. 2 and
The heat-resistant synthetic resin non-woven fabric 5 is sandwiched between the heat-fusible resin film 6 on the aluminum foil side and the heat-fusible resin film 7 on the innermost side, and these are integrated by heat-fusion to create a three-layer internal adhesive resin. It is composed of layer 8. Further, FIG. 4 shows a cross section of another exterior film of the present invention. The inner adhesive resin layer 8' arranged on the inner surface of the aluminum foil 2 has a two-layer structure, each consisting of a heat-adhesive resin film 6 on the aluminum foil side and a heat-resistant synthetic resin nonwoven fabric 5. The fusible resin film 7 has a five-layer structure as a whole. Heat-resistant synthetic resin nonwoven fabric 5
The heat-fusible resin films 6, 7 or 6, 6 located on both sides are heat-sealed, and the resin penetrates into the interior, so there are no voids, and the vapor of the electrolyte flows in the thickness direction. does not pass through. The heat-resistant synthetic resin nonwoven fabric 5 is preferably a nonwoven fabric made of short polyethylene terephthalate fibers that does not use a binder in terms of heat resistance, physical strength, and electrolyte resistance. In addition, in order to prevent moisture and electrolyte from permeating, the resin of the resin films on both sides and the innermost heat-adhesive resin film must penetrate into the interior through heat fusion and become physically firmly integrated with them. There is. Therefore, the fiber density (basis weight) is less than 0.5g/ ^cm3 , and the thickness
It is preferably 0.05 mm or less. The basis weight is
If it is 0.5 g/cm ³ or more, the resin will not penetrate sufficiently between the fibers, resulting in fine voids. Furthermore, if the thickness of the synthetic resin nonwoven fabric is 0.05 mm or more, there is a limit to the flow of the fused resin on both sides, and the infiltration into the inside of the nonwoven fabric is insufficient, resulting in the formation of voids. The innermost resin film 7 is for thermally adhering to the current collector metal and for thermally sealing it at the battery periphery, and is made of ethylene or propylene monomer.
For 100 parts by weight, acrylic acid, methacrylic acid,
It is obtained by copolymerizing or graft polymerizing 0.01 to 10 parts by weight of αβ-unsaturated carboxylic acids such as itaconic acid, fumaric acid, maleic acid, and maleic anhydride.
This innermost resin film 7 has the heat sealability and solvent resistance inherent to non-polar crystalline polyolefin, and has good thermal adhesion to current collector metals such as aluminum and nickel due to the presence of carboxyl groups. be. If the amount of carboxylic acid is less than 0.01 parts by weight, there will be no adhesion effect to metals, and if it is more than 10 parts by weight, the inherent organic solvent resistance of polyethylene or polypropylene will be impaired.
Due to increased hydrophilicity, organic electrolyte batteries have problems such as the risk of adsorption or contamination of moisture, which can cause performance deterioration. Furthermore, this innermost resin film 7 has a thermal fusion temperature lower than the melting point of the heat-resistant synthetic resin nonwoven fabric 5 by at least 20°C,
When thermally adhering to the current collector metal or thermally sealing the battery periphery, it is quickly fused at a low temperature without reducing the physical strength of the heat-resistant synthetic resin nonwoven fabric 5, and the current collector and aluminum foil are bonded together. It is possible to prevent the aluminum foil from being exposed to the inside of the battery due to contact with the battery or the formation of pinholes in the inner film. If the difference in melting point between this innermost resin film and the heat-resistant synthetic resin nonwoven fabric is less than 20°C, the nonwoven fabric will also soften due to heat, and there is a risk that the current collector will come into contact with the aluminum foil in the exterior film. There is no effect of the presence of heat-resistant synthetic resin nonwoven fabric. The heat-resistant resin film 1 has a melting point or softening point that is 20 to 30°C higher than the heat-sealing temperature of the innermost resin film 7, and is laminated with the aluminum foil 2 to prevent pinholes and corrosion of the aluminum foil. It is intended to prevent heat-bonding and provide workability for thermal bonding to the packaging material, and polyester, nylon, or the like with a thickness of about 12 to 50 μm can be used, but the material is not particularly limited thereto. The aluminum foil 2 prevents the electrolyte from evaporating to the outside and moisture in the outside air from entering the power generation element, and also provides rigidity to the battery periphery, and must have a thickness of 9 μm or more. In addition, heat-resistant resin film 1
and aluminum foil 2 are bonded together using an adhesive or adhesive film that is stable against heat received during the battery manufacturing process. Furthermore, in the present invention, the aluminum foil film 6 constituting the inner adhesive resin layer 8 may be the same as the innermost resin film 7, or may have metal adhesiveness and be the same as the innermost resin film 7. Although other polyolefin resin films with adhesive properties may be used, the aluminum foil 2 can be bonded by heat fusion without using a solution adhesive.
are laminated on. An example of the structure of a flat battery in which a power generation element is packaged using the exterior film of the present invention will be explained with reference to FIG. A positive electrode current collector 10 and a negative electrode current collector 11 are each heat-sealed to the exterior film 9 which is folded into two sheets or two. The welding temperature at this time is preferably 150°C to 200°C. Titanium, stainless steel, aluminum, etc. are used for the positive electrode current collector 10, and nickel, stainless steel, etc. are used for the negative electrode current collector 11. Moreover, its thickness is 30 to 80μ. The positive electrode mixture layer 12 consists of a positive electrode active material, carbon black as a conductive material, and an adhesive. Metal oxides such as manganese dioxide, metal sulfides, or carbon fluoride are used as the positive electrode active material. Polytetrafluoroethylene is used as the binder. On the other hand, an alkali metal such as lithium is used for the negative electrode 13. Separator 14 is a polypropylene nonwoven fabric. The electrolytic solution used is an aprotic, high dielectric constant, low viscosity organic solvent such as γ-butyrolactone in which an inorganic salt such as lithium fluoride or lithium perchlorate is dissolved. The separator 14 is impregnated with this electrolyte. The surroundings of these power generation elements are thermally welded with the exterior film 9. The temperature conditions are 150°C to 200°C. In addition, the positive electrode current collector 10 and the negative electrode current collector 11 exposed through the window 15 formed in the exterior film 9 serve as the positive and negative electrode terminals. By providing a layer of heat-resistant synthetic resin nonwoven fabric in the adhesive resin layer of the exterior film in this way, it was possible to prevent pinholes from occurring in the inner film during the heat welding process around the battery during battery construction. As a result, the electrolyte did not reach the aluminum foil in the exterior film through the pinhole, and corrosion of the aluminum was eliminated. Furthermore, by providing a layer of heat-resistant resin nonwoven fabric,
When heat-sealing the exterior film, there is no contact between the current collector metal and the aluminum foil in the exterior film.
As a result, the elution of the aluminum foil in the outer film due to battery formation could be prevented. As a result of eliminating corrosion of the aluminum foil in the above two processes,
The number of defects caused by electrolyte evaporation from the leached portion of the aluminum foil of the exterior film and moisture in the outside air entering the power generation element has been drastically reduced. The following table compares the storage performance of flat organic electrolyte batteries stored at a temperature of 60°C and a relative humidity of 90% in terms of failure rate. The conventional exterior film has a three-layer structure of polyester film (thickness 12μ)/aluminum foil (9μ)/carboxyl group-containing polypropylene film (80μ). Invention 1 uses an exterior film consisting of polyester film (12μ)/aluminum foil (9μ)/carboxyl group-containing polypropylene film (40μ)/polyester nonwoven fabric (50μ)/carboxyl group-containing polypropylene film (40μ). In addition, the present invention 2 is polyester film (12μ) / aluminum foil (9μ) / carboxyl group-containing polypropylene film (40μ) / polyester non-woven fabric (50μ) / carboxyl group-containing polypropylene film (40μ) / polyester non-woven fabric (50μ) / carboxyl-containing polypropylene This is an exterior film made of film (40μ). The power generating elements are all 30 mm wide and 60 mm long, with a thickness of 1.6 mm including the positive and negative electrode current collectors, and each of the above-mentioned exterior films is 40 mm wide and 70 mm long, making only the total thickness of the battery. It was changed depending on the thickness of the exterior film. Note that carbon fluoride was used as the positive electrode, lithium was used as the negative electrode, and lithium fluoride dissolved in γ-butyrolactone at a concentration of 1 mol/mol was used as the electrolytic solution. In each case, 100 batteries were used.

[Table] Effects of the invention As is clear from the results in the previous table, in the present invention, a heat-fusible resin film is heat-sealed into the exterior film, and a heat-resistant synthetic resin nonwoven fabric with resin permeated inside is made from aluminum foil. By placing it inside,
Even if pinholes occur in the heat-fusible resin film, corrosion or elution of the aluminum foil can be maintained in a state where there is no or almost no corrosion or elution. In addition, in order to maintain good air-tightness and liquid-tightness, it is possible to significantly improve battery storage performance by eliminating evaporation of organic electrolyte to the outside and preventing moisture from entering the power generation element in the outside air during battery storage. did it.

[Brief explanation of drawings]

1 and 2 are sectional views showing the exterior film of a conventional flat battery, FIGS. 3 and 4 are sectional views of the exterior film in an embodiment of the present invention, and FIG. 5 is an embodiment of the present invention. FIG. 1...Heat-resistant resin film, 2...Aluminum foil, 3, 8, 8'...Inner adhesive resin layer, 4...
...Resin film, 5...Heat-resistant synthetic resin nonwoven fabric,
6, 7... Heat-fusible resin film, 12... Positive electrode, 13... Negative electrode, 14... Separator.

Claims (1)

[Scope of Claims] 1. A multilayer film consisting of a heat-resistant resin film, an aluminum foil, and an inner adhesive resin layer, impregnated with a positive electrode mixture layer, an alkali metal for the negative electrode, and an organic electrolyte, and positioned between the positive and negative electrodes. The battery is equipped with a flat power generating element made of a separator, and the inner adhesive resin layer has a heat-resistant synthetic resin film between an aluminum foil side resin film and an innermost resin film each made of a heat-fusible resin film. A flat battery having at least a three-layer structure with resin non-woven fabric arranged thereon, resin films on both sides of the heat-resistant synthetic resin non-woven fabric being heat-sealed and resin permeating the inside. 2 A patent in which the inner adhesive resin layer has a two-layer structure of a heat-fusible resin film on the aluminum foil side and a heat-resistant synthetic resin nonwoven fabric, and the innermost layer is a heat-fusible resin film, making the entire structure five-layered. A flat battery according to claim 1. 3. The heat-resistant synthetic resin nonwoven fabric is made of polyethylene terephthalate staple fibers that do not use a binder,
And the fiber density is 0.5g/ ^cm3 or less, and the thickness is 0.05
3. The flat battery according to claim 1 or 2, which has a diameter of less than mm. 4. Claim 1 in which the innermost resin film is made of carboxyl group-containing polyethylene or polypropylene having a thermal fusing temperature that is at least 20°C lower than the melting point of the heat-resistant synthetic resin nonwoven fabric.
The flat battery according to item 1 or 2. 5. An exterior film for a battery with a flat power generation element, which has a multilayer film structure consisting of a heat-resistant resin film, aluminum foil, and an inner adhesive resin layer.
The inner adhesive resin layer has at least a three-layer structure in which a heat-resistant synthetic resin nonwoven fabric is arranged between a heat-fusible resin film on the aluminum foil side and a heat-fusible resin film on the innermost side, and the heat-resistant synthetic resin Resin films on both sides of the non-woven fabric are heat-sealed, and the resin penetrates into the inside of the non-woven fabric to form the exterior film for flat batteries.