JPH029498Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an improved outer packaging material for flat, thin lithium batteries, and more specifically to a metal current collector housed inside a sheet-shaped lithium battery using a non-aqueous electrolyte. The present invention provides an outer covering material for a flat, thin lithium battery that has good adhesion to the body, excellent moisture resistance, prevents dissipation and leakage of an organic electrolyte, and can prolong the life of the battery.

Conventional thin batteries include stacked flat batteries made by stacking multiple flat Lecrancier-type cells, and flat Lecrancier-type cells wrapped in outer packaging material.
The terminal was exposed from a part of the outer packaging material. However, all of these batteries are made of water-based neutral salt electrolyte, and the packaging material used is one in which ethylene-acrylic acid copolymer resin, etc. with metal adhesive properties are laminated with adhesive on the inner layer. It had been.

Furthermore, in recent years there has been an increasing demand for flat, thin batteries as devices become smaller and thinner, such as with electronic watches and smaller and thinner calculators. Lithium batteries have been developed that use a non-aqueous electrolyte as a negative electrode active material and a non-aqueous electrolyte. However, in the case of nonaqueous electrolyte-based thin batteries, conventionally used packaging materials have problems such as peeling of the laminated structure due to the organic solvent electrolyte, deterioration of adhesion to metals, and poor sealing. However, nothing good was obtained.

The present invention was developed in view of the above-mentioned circumstances, and is an outer casing for thin lithium batteries that has sufficient adhesion to the metal current collector, prevents evaporation of the electrolyte or moisture infiltration to the outside, and has good storage stability. As a result of repeated research on the material and lamination method of the internally adhesive resin, we have developed an intermediate material that uses maleic anhydride grafted polyethylene as the internally adhesive resin and is non-conductive and has heat and solvent resistance. By laminating the film and the inner adhesive resin by heat fusion instead of adhesive, it is stable against organic electrolytes and has excellent adhesion to metal current collectors such as nickel.
The inventors have discovered that the adhesion of the battery periphery by the inner adhesive resin is strong and prevents electrolyte from leaking from the battery terminals and the battery periphery, and has completed this invention.

The present invention will be explained in detail below with reference to the drawings. That is, the present invention consists of a laminated structure of an aluminum foil 2 with a thickness of 9μ or more bonded to a heat-resistant resin film 3, an intermediate heat-resistant and solvent-resistant film 4, and an inner adhesive resin 1 made of maleic anhydride grafted polyethylene. The present invention is an outer covering material for a flat and thin lithium battery, characterized in that an intermediate heat-resistant/solvent-resistant film 4 and an inner adhesive resin 1 are laminated by heat fusion.

Here, the inner adhesive resin 1 is for thermally adhering to the metal current collectors 6 and 7 and thermally sealing the battery periphery, and is a continuous film with a thickness of 25 to 80 μm.
It is made by graft polymerizing 0.01 to 10 parts by weight of maleic anhydride to 100 parts by weight of low-density, medium-density or high-density polyethylene, and using an intermediate heat-resistant/solvent-resistant film 4 such as a nylon film and an adhesive. They are laminated by heat fusion instead of heat fusion. The internal adhesive resin 1 is a non-polar crystalline polyolefin, that is, polyethylene has inherent heat-sealability and solvent resistance, and the presence of the carboxyl group of graft-polymerized maleic anhydride makes it suitable for aluminum, zinc, stainless steel, and nickel. It has good thermal adhesion with current collector metals 6 and 7 such as, etc., and also has good thermal adhesion with intermediate heat-resistant and solvent-resistant films 4 such as nylon. The amount of maleic anhydride
If it is less than 0.01 part by weight, it has no adhesive effect on metal, and 10
If the amount is more than 1 part by weight, the inherent organic solvent resistance of polyethylene will be impaired, and since the polyethylene will become hydrophilic, there will be problems such as the risk of adsorption and contamination of water, which will cause performance deterioration in lithium batteries.

The heat-resistant resin film 3 has a melting point or softening point that is 20 to 30 degrees Celsius higher than the thermal bonding temperature of the inner adhesive resin 1, and is laminated with the aluminum foil 2 to prevent pinholes and corrosion in the aluminum foil. It provides heat bonding workability to the packaging material, and polyester, nylon, etc. with a thickness of about 12 to 50 μm can be used, but there is no particular limitation.

The aluminum foil 2 prevents the electrolyte from evaporating to the outside and moisture from entering from the outside, and also provides rigidity to the periphery of the thin battery, and must have a thickness of 9 μm or more. Aluminum foil thinner than 9μ may cause pinholes. However, if the thickness is 9μ or more, there will be almost no pinholes, and the barrier properties of the foil will prevent the evaporation of the electrolyte and the intrusion of moisture from the outside. The heat-resistant film 3 and the aluminum foil 2 are bonded together using an adhesive or adhesive film that is stable against heat received during the battery manufacturing process.

The intermediate heat-resistant/solvent-resistant film 4 is a continuous film with a thickness of 12 μm to 40 μm made of polyester, nylon, saponified resin of ethylene vinyl acetate, etc., which has a melting point 20 to 30° C. higher than that of the internal adhesive resin and solvent resistance. By arranging the aluminum foil 2 and the inner adhesive resin 1 in a sandwich pattern, the aluminum This prevents the foil 2 from being exposed inside the battery and causing a short circuit, and also prevents deterioration of the adhesion between the packaging materials due to penetration of the electrolytic solution, providing stable sealing workability and improved storage stability. In the present invention, the inner adhesive resin 1
and the intermediate heat-resistant/solvent-resistant film 4 are laminated by heat fusion without using an adhesive. γ-Butyrolactone, etc. used in lithium batteries has strong permeability to polymers and swelling properties, and when using adhesives such as urethane, swelling of the adhesive layer or deterioration of adhesive strength is unavoidable. Because of the strong interfacial adhesion due to the reactivity of the grafted maleic anhydride, there is no deterioration in adhesive strength, and the adhesion improves with the heat of the battery manufacturing process and with storage time.

When the present invention is applied to a flat thin lithium battery, two flat thin lithium battery outer covering materials 5 are cut into specified dimensions and shapes and provided with electrode windows 8 and 8' of appropriate size. A negative electrode current collector 6 made of a nickel sheet having a smaller shape than the outer covering material 5 and having a thickness of about 20 to 100 μm is thermally bonded to the inside of one of the outer covering materials 5 by heating and pressurizing. For example, the inner surface may have a thickness of 20 mm with a carbon coating on the back surface.
A positive electrode current collector 7 made of a hard aluminum sheet having a shape smaller than the outer covering material 5 of about 100μ is heated and pressurized to thermally bond the negative electrode current collector 6 and the positive electrode current collector 7, In between, a separator 9 is made of a nonwoven fabric made of polypropylene or the like impregnated with an electrolytic solution in which an alkali metal salt such as lithium borofluoride is dissolved in an aprotic, high dielectric constant, low viscosity organic solvent such as γ-butyrolactone. A battery element in which a positive electrode layer 10 and a lithium negative electrode 11 are laminated is sandwiched and pressed together, and the peripheral edges of the outer envelope material 5 are heated and pressurized to thermally fuse and seal to form a flat, thin lithium battery. It is. In this case, the positive and negative terminals are the negative electrode current collector 6 and the positive electrode current collector 7 exposed through the windows made in the outer envelope material 5.

As mentioned above, the present invention has the aluminum foil 2 having the original gas barrier effect and the inner adhesive resin 1.
Since it is based on inert polyethylene, it does not swell with organic electrolytes such as γ-butyrolactone, propylene carbonate, dioxolane, and 3-methyl-2oxazoline, so it has intermediate heat and solvent resistance. Combined with the vapor blocking effect of Film 4, it can prevent permeation and evaporation of the electrolyte, and in the case of lithium batteries, it also provides sufficient moisture resistance, which is required since the negative electrode lithium has a high reactivity with water. Therefore, the increase in internal resistance is small and the life of the battery can be extended. Furthermore, the maleic anhydride grafted polyethylene on the inner surface has strong adhesion strength to metals, and the adhesion to current collector metals to be bonded, such as nickel and aluminum, is strong, and there is no leakage of electrolyte from the terminal portions. Furthermore, in the present invention, since the internal adhesive resin 1 is firmly laminated with the intermediate heat-resistant and solvent-resistant film 4 by heat fusion, there are few factors that cause deterioration of the adhesion between the laminated structures, and it can be stored for a long time.
There is no delamination during use, making full use of the high reliability and long life of lithium batteries.

[Brief explanation of drawings]

FIG. 1 is a partially enlarged sectional view of the present invention, and FIG. 2 is a sectional view of one embodiment of a flat, thin lithium battery to which the present invention is applied. DESCRIPTION OF SYMBOLS 1... Inner adhesive resin, 2... Aluminum foil, 3... Heat-resistant film, 4... Intermediate heat-resistant and solvent-resistant film, 6, 7... Metal current collector.

Claims (1)

[Scope of utility model registration request] The outer packaging material for a flat thin lithium battery includes, in order from the outside to the inside, a heat-resistant resin film 3, an aluminum foil 2 with a thickness of 9μ or more pasted to this film 3, and an aluminum foil 2 pasted to this foil 2. It is made by laminating a heat-resistant and solvent-resistant film 4 and an inner adhesive resin 1 made of maleic anhydride grafted polyethylene, and the heat-resistant and solvent-resistant film 4 and the inner adhesive resin 1 are laminated by heat fusion. An outer packaging material for flat and thin batteries characterized by the following.