JPH0458146B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a flat, thin battery and its outer packaging material. <Description of prior art and development progress> Conventionally, flat and thin batteries using manganese dioxide as the positive electrode active material, zinc as the negative electrode active material, and a neutral salt electrolyte have been commercially available under the trade name of "Paper Battery," for example. It's here. A cross-sectional view of this flat, thin battery is approximately as shown in FIG. That is, in FIG. 1, the negative electrode (zinc plate) 11
and a positive electrode current collector 14, a parator 12 impregnated with an aqueous solution of zinc perchlorate, which is an electrolytic solution, and a positive electrode mixture (a mixture of manganese dioxide and carbon black).
13, and the whole is packaged with an outer packaging material 10. Note that a window is partially opened in this outer covering material 10, and the positive electrode current collector 14 exposed through this window.
becomes the positive electrode terminal 15, the negative electrode 11 and the outer covering material 10
The metal plate sandwiched between them serves as a negative electrode terminal 16. In FIG. 1, the outer wrapper 10 is depicted as a single layer sheet;
As shown in the enlarged cross-sectional view of the figure, from the outside: heat-resistant film 21 / adhesive 22 / aluminum foil 23 / adhesive 24 / heat-resistant resin film 25 / adhesive 2
6/ It is a multilayer sheet in which metal adhesive resin 27 is laminated. Incidentally, recent advances in electronics such as ICs and LSIs have been remarkable, and electronic precision equipment that uses these devices is increasingly required to be highly accurate and multi-functional. High energy density and long-term reliability are required. Furthermore, small portable devices with low power consumption, such as calculators and cameras, are being designed to be more fashionable and more functional, such as dramatically smaller size and weight. Therefore, in terms of being small, lightweight, thin, and fashionable,
Although the above-mentioned flat and thin batteries are extremely excellent, they do not necessarily have the best energy density. To date, the battery with the highest energy density is said to be a lithium battery. This lithium battery is metal lithium or lithium-
It uses a lithium-based alloy such as aluminum (Li-Al) alloy as a negative electrode active material and a non-aqueous electrolyte, and has the following characteristics (a) to (c). (a) Metallic lithium has a standard electrode potential E=-
It has the lowest potential of all substances at 3.045V, and the lowest electrochemical equivalent of 0.26g/Ab among solid substances, so it is a high voltage battery (3V or more) and has a very high energy density. It could be a battery. (b) Since it uses an organic electrolyte, it has a wide operating temperature range. (c) It is expected to have a long shelf life of 5 years or more. Therefore, if it were possible to manufacture a flat thin lithium battery instead of the conventional flat thin manganese dioxide/zinc battery, it would be possible to produce a flat thin lithium battery that has high voltage, high energy density, long-term storage, and is also small, lightweight, and thin. , a fashionable battery can be obtained. Therefore, a rough cross-sectional view of an expected flat thin lithium battery is as shown in FIG. 3, for example. That is, a positive electrode current collector 31 and a negative electrode current collector 35 are respectively heat-sealed to the outer packaging material 30 which is folded into two sheets or two. A positive electrode mixture 32, a separator 33 impregnated with an organic electrolyte, and a negative electrode 34 made of lithium or a lithium-based alloy are sandwiched between the positive electrode current collector 31 and the negative electrode current collector 35 in this order. However, the outer packaging material 3 of flat thin lithium batteries
Unlike the conventional manganese dioxide/zinc-based flat thin battery outer covering material 10, extremely excellent moisture resistance and resistance to organic electrolytes are required. Further, as with conventional flat thin batteries, it goes without saying that thermal adhesion to the current collectors 31 and 35 is required. In view of these circumstances, the inventors of the present invention have so far produced and studied various outer packaging materials. For example, if the conventional outer packaging material 10 in which an inner adhesive resin is laminated using an adhesive is used as is,
The organic electrolyte penetrates into the heat-resistant resin film 25.
and the metal adhesive resin 27, and between the heat-resistant resin film 25 and the aluminum foil 23. Similar peeling or deterioration of adhesive strength due to penetration of organic electrolyte also occurred when urethane-based adhesives or epoxy-based adhesives were used. From these experimental results, it can be concluded that so-called adhesives such as solvent-based adhesives and non-solvent adhesives swell due to the penetration of organic electrolytes, which deteriorates their adhesive strength and makes them easier to peel off. I had no choice. Therefore, the present inventors did not use an adhesive on the inner side of the aluminum foil of the outer wrapping material 30, and produced a prototype outer wrapping material using only a heat-fusible resin. This is the fourth
The cross-sectional view in the figure shows, in order from the outside: heat-resistant film 40 / adhesive 42 / aluminum foil 43 /
Laminated material 40 having a layered structure of heat-fusible resin 44
It is. Note that since the organic electrolyte does not penetrate beyond the aluminum foil 43, the heat-resistant film 4
1 and the aluminum foil 43 can be bonded together using a suitable adhesive. Here, heat-fusible resin 4
Examples of 4 include ethylene-(meth)acrylic acid derivative copolymer, ethylene-glycidyl(meth)acrylate-vinyl acetate terpolymer, and polyolefin graft-modified with unsaturated carboxylic acid. Polyolefin graft-modified with unsaturated carboxylic acid was superior in terms of fusion strength and stability over time, and polypropylene graft-modified with unsaturated carboxylic acid was particularly excellent. In this way, by using the laminated material 40 shown in FIG.
Although the problem of deterioration of the adhesion between the outer envelope material 30 and the adhesive strength due to penetration of the organic electrolyte was solved, on the other hand, a new problem occurred by using the laminated material 40 shown in FIG. I did it. That is, the current collectors 31 and 35 and the aluminum foil 43 in the laminated material 40 were short-circuited. There were two causes for the short circuit. One is that when the laminated material 40 is used as the outer covering material 30 and is heat-sealed to the current collectors 31 and 35, a small pinhole is created in the heat-sealable resin 44, and the aluminum in the laminated material 40 is formed through the heat-sealed resin 44. This causes a short circuit to the foil 43. Another cause of the short circuit is that when the outer covering material 30 is heat-sealed together, the current collectors 31 and 35 break the heat-sealing resin 44 at the seal edges, causing a short circuit with the aluminum foil 43. That's what happens. This state is shown in the partial sectional view of FIG. The x in the figure is the torn part. In order to prevent this short circuit, it was considered that another sheet should be interposed between the aluminum foil 43 and the heat-fusible resin 44, which would not cause pinholes due to the heat during heat-sealing. This is shown in the cross-sectional view of FIG. 6, where 61 is nylon, ethylene-vinyl alcohol copolymer, polyester (polyethylene terephthalate), or polyolefin having a higher melt viscosity than the heat-fusible resin 44 during heat-sealing. It is a film of However, nylon and ethylene-vinyl alcohol copolymers have hygroscopic properties and will absorb moisture from their end surfaces, so there is a risk that the lithium or lithium-based alloy used as the negative electrode active material will react with the invading moisture. Polyester is not hygroscopic and has excellent organic solvent resistance, but heat-fusible resin 44 and polyester usually do not have heat-fusibility (polyester-based heat-fusible resin can be heat-fused to polyester, but , it swelled in the organic electrolyte), and sufficient adhesive strength could not be obtained. Polyester may be used as the film 61, and an adhesive may be used between the heat-fusible resin 44 and the film 61, but as described above, the adhesive peels off due to penetration of the organic electrolyte. The problem seemed intractable. However, the present inventors solved this problem using an unexpected method of using a heat-resistant resin film whose both sides were treated with non-equilibrium plasma (low-temperature plasma) using an inorganic gas. <Summary of the Invention> That is, the present invention provides a battery in which a flat power generation element is packaged from the outside with an outer covering material consisting of a heat-resistant film, an aluminum foil, and a multilayer inner adhesive layer, and At least a three-layer structure with a heat-resistant resin film treated with non-equilibrium plasma (low-temperature plasma) using an inorganic gas on both sides between the heat-fusible resin on the aluminum side and the heat-fusible resin on the innermost surface. The flat non-aqueous electrolyte battery is characterized in that the inner adhesive layer is laminated by heat fusion. According to the present invention, the heat-resistant resin film is arranged inside the aluminum foil of the outer covering material, and even if a pinhole occurs in the internal heat-sealable resin, the aluminum foil and the current collector In addition to preventing electrical contact, since no adhesive is used, it is possible to prevent deterioration of adhesive strength due to penetration of organic electrolyte. <Embodiment of the invention> The details of the present invention will be explained below using examples.
FIG. 7 of the drawings shows a sectional view of an outer wrapping material according to an embodiment of the present invention. In the figure, 71 means a heat-resistant film such as polyester or nylon, and this heat-resistant film 71 has a melting point 20 to 30°C higher than the heat-fusion temperature of the heat-fusible resin 76, and is laminated with the aluminum foil 73. This prevents the occurrence of pinholes and corrosion in the aluminum foil 73, and also provides heat-sealing workability to the outer wrapping material 70. This heat-resistant film 71 and aluminum foil 73 are pasted together with an adhesive or an adhesive film 72 interposed therebetween. Further, 75 is a heat-resistant resin film whose both sides are treated with non-equilibrium plasma (low-temperature plasma) using an inorganic gas, and for example, a polyester film (polyethylene terephthalate film) is suitable. That is, at a gas pressure of 0.01 to 1.0 Torr,
Plasma is formed by applying high frequency power,
By applying this to the surface of the polyester film, it is possible to create a polyolefin-based metal adhesive resin with carboxyl groups and the like, which was previously considered impossible, without changing the original properties of the polyester film such as strength and heat resistance. The surface has been modified to allow thermal bonding. Oxygen gas has shown the best results as the inorganic gas used, but its adhesion effect is thought to be caused by a combination of etching of the film surface by plasma, introduction of functional groups such as carboxyl groups, or surface crosslinking. As expected, nitrogen gas, argon gas, etc. can be used in combination with oxygen gas as the inorganic gas. The innermost heat-fusible resin 76 may be made of, for example, ethylene-(meth)acrylic acid copolymer, ethylene-glycidyl(meth)acrylate-vinyl acetate, or polyolefin graft-modified with unsaturated carboxylic acid, which adheres to metal. As mentioned above, polyolefin graft-modified with an unsaturated carboxylic acid is preferable because of its resistance to organic electrolytes. On the other hand,
α, β- such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, maleic anhydride, etc.
It is preferable to graft polymerize 0.01 to 10 parts by weight of unsaturated carboxylic acid. Further, as the aluminum foil side heat-fusible resin 74, any resin that can be used as the innermost heat-fusible resin 76 can be used, but polyethylene or the like can also be used. Aluminum foil (for example, thickness 9μ or more) 73,
The aluminum side heat-fusible resin 74, the heat-resistant resin film 75 whose both sides have been treated with non-equilibrium plasma, and the innermost heat-fusible resin 76 must be laminated by heat-fusion without using adhesive. It is. A cross-sectional view of a flat thin battery obtained using this outer wrapping material 70 is similar to that shown in FIG. The negative electrode current collectors 35 are each heat-sealed. The thermal fusion temperature at this time is preferably 150 to 200°C. Titanium, stainless steel, aluminum, etc. are used for the positive electrode current collector 31, and nickel, stainless steel, etc. are used for the negative electrode current collector 35. Moreover, its thickness is 30 to 80μ. The positive electrode mixture layer 32 consists of a positive electrode active material, carbon black as a conductive material, and a binder. 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, the negative electrode 34 is made of lithium or a lithium-based alloy such as a lithium-aluminum alloy. The separator 33 is a nonwoven fabric such as polypropylene. The organic electrolyte consists of an aprotic high dielectric constant, low viscosity organic solvent such as γ-butyrolactone, lithium fluoride,
A solution containing an inorganic salt such as lithium perchlorate is used. As described above, according to the present invention, pinholes are formed in the heat-fusible resin layer when the outer wrapping material and the current collector are heat-sealed and when the outer wrapping materials are heat-sealed together. Even if it occurs,
The presence of the heat-resistant resin film prevents electrical contact between the current collector and the aluminum foil, thereby preventing a short circuit between the outer wrapping material and the current collector. In addition, the layers of the outer covering material, current collector, and outer covering material have strong adhesive strength, and peeling does not occur due to penetration of the organic electrolyte. The present invention will be explained below with reference to Examples and Comparative Examples. <Example> Both sides of a biaxially stretched polyethylene terephthalate film with a thickness of 25 μm were treated with non-equilibrium plasma (low temperature plasma) using an inorganic gas mainly composed of oxygen gas, and one side was coated with ethylene containing 8% acrylic acid.
A 40μ thick acrylic acid copolymer resin was applied by melt extrusion coating (resin temperature 280°C), and the aluminum foil surfaces of a laminated material with a layered structure of polyester film/adhesive/aluminum foil were overlapped and heat-sealed. Next, this other plasma-treated surface is melt-extruded and coated with polyethylene graft-modified with maleic anhydride to form a polyester film 71 / adhesive 72 / aluminum foil 73 / ethylene-acrylic acid copolymer resin 74 / double-sided plasma-treated polyester film. An outer packaging material having a layer structure of 75/maleic anhydride-modified polyethylene 76 was obtained. When the flat non-aqueous electrolyte battery shown in FIG. 3 was fabricated using this outer casing material, there was no problem of short circuit between the current collectors 31 and 35 and the aluminum foil 73 in the outer casing material 70. Nakatsuta. In addition, polyester film 75 with plasma treatment on both sides and ethylene-
The adhesive strength between acrylic acid copolymer resin 74 and maleic anhydride modified polyethylene 76 was good as shown in Table 1. <Comparative Example> An outer wrapping material was created in the same manner as in the example, using an untreated polyester film and a polyester film whose both sides were subjected to corona discharge treatment instead of the polyester film whose surfaces were plasma-treated. As shown in Table 1, the adhesive strength between this untreated polyester film, the corona discharge-treated polyester film, the ethylene-acrylic acid copolymer resin 74, and the maleic anhydride-modified polyethylene 76 was either nonexistent or unstable; It peels off due to the action of electrolyte (γ-butyrolactone) during storage,
It was unsuitable for use as an outer covering material. 【table】

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views of a conventional manganese dioxide/zinc-based flat thin battery and its outer packaging material;
Figure 3 is a cross-sectional view of a flat, thin battery with lithium as the negative electrode, Figures 4 and 6 are cross-sectional views of conventional outer packaging materials, and Figure 5 is a cross-sectional view of a flat, thin battery with lithium as a negative electrode. Partial sectional view, FIG. 7 is a sectional view of the outer wrapping material of the present invention. 10, 30, 40, 60, 70...outer packaging material,
21,41,71...Heat-resistant film, 22,2
4, 26, 42, 72...adhesive, 23, 43,
73... Aluminum foil, 44... Heat-fusible resin, 74... Aluminum foil side heat-fusible resin, 7
3... Heat-resistant resin film treated with non-equilibrium plasma (low-temperature plasma) on both sides, 76... Innermost heat-sealing resin, 31... Positive electrode current collector, 32... Positive electrode mixture, 33... Separator , 34... negative electrode, 35
...Negative electrode current collector.

Claims (1)

[Scope of Claims] 1. A battery in which a flat power generating element is packaged from the outside with an outer covering material consisting of a heat-resistant film, an aluminum foil, and an inner adhesive layer with a multilayer structure, wherein the inner adhesive layer is made of aluminum. At least three layers of polyester film with improved thermal adhesive properties that have been treated with non-equilibrium plasma (low-temperature plasma) using an inorganic gas on both sides between the side thermal adhesive resin and the innermost thermal adhesive resin. 1. A flat, thin non-aqueous electrolyte lithium battery characterized in that the inner adhesive layer is laminated by heat fusion. 2. The flat and thin non-aqueous electrolyte lithium battery according to claim 1, wherein the heat-resistant resin film disposed between the inner adhesive layers is a biaxially stretched polyethylene terephthalate film.