JPS61176054A - Flat cell - Google Patents

Abstract

PURPOSE:To obtain a flat cell with hermetically good sealing, constant external shaping, and no short-circuiting by composite-integrating the sealing member of a container peripheral part with different-natured polyolefine resin layers. CONSTITUTION:Between both peripheries of a pair of negative and positive polar terminal plates 1 and 6 facing each other, a denatured polyethylene sealing material 7, processed in a window-frame shape, is interposed, and the member 7 is deposited, with pressurizing and heating, at the peripheries of the terminal plates 1 and 6, so that a cell chamber, in which an electric-generation element is housed, is hermetically-sealed. The constitution of member 7 in view of material is achieved by laminating, in a three-layers composite structure, resin layers 7' having high viscosity in fused state of the depositing temperature selected out of good sulvent-proof polyoletine resins on both inner and outer sides of a base material 7'' serving as a core with lower viscosity in fused state than that of resin layer 7'. Since this composition realizes hermetically-sealed good deposition under the condition in which the sealing member is less deformed at the time of deposition, the cell is enabled to be sealed with hermetically good sealing and less deformation of the sealing member.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a flat battery consisting of at least one unit cell in which a flat power generation element is sealed with a battery container for positive and negative electrodes and a heat-fusible sealing material. This is related to improvements.

2. Description of the Related Art In recent years, with the diversification of various electronic devices, the shapes of batteries have also become smaller and thinner.

In order to achieve thinness, the construction method of power generation elements is an important issue, but the sealing method of batteries or unit cells is an even more important technical issue. Conventionally, in the case of cylindrical batteries and button batteries, a gasket is interposed between the battery container and the battery lid, and the opening end of the battery container is folded inward to seal the container, lid, and There is a limit to the mechanical strength due to the thinning of the gasket, and it is usually 1.5tWM, and even the prototype is 1.
The thickness of the unit cell at zero is considered to be the limit for thinning. Therefore, as a sealing structure to further reduce the thickness of the battery, a flat or film-like structure is used with adhesive or heat-fusible resin, which is used in batteries commonly called ``zero-sheet batteries'' or ``paper batteries.'' A method of sealing the battery container has been proposed.An important technical problem in this case is that as batteries become thinner, the distance between the positive and negative electrodes becomes narrower, making it difficult to ensure that the insulation between the two electrodes is maintained. Furthermore, the smaller and thinner the battery is, the more stringent the requirements for dimensional accuracy become, making it difficult to ensure dimensional stability that meets these requirements.

Naturally, a system with high energy density should be selected as the power generating element of such a small and thin battery, and for this reason, a non-aqueous electrolyte with lithium as the negative electrode and an inorganic salt dissolved in an organic solvent is used. It is best to use a so-called non-aqueous electrolyte lithium battery using various solid active materials such as manganese dioxide and carbon fluoride as the positive electrode.

However, as mentioned above, these nonaqueous electrolytes use organic solvents, such as ester or ether solvents such as γ-butyrolactone, propylene carbonate, dimethoxyethane, dioxolane, and tetrahydrofuran, so adhesives used as sealants or heat-fusible resin,
Furthermore, it is necessary to select resin materials such as gaskets that are chemically stable in the above-mentioned solvents, and materials that meet this condition include polyolefin and silicone materials.

Limited to resins such as fluororesin, heat-weldable.

If conditions such as airtightness are added to the selection, polyolefin resins are considered to be the most appropriate.

Problems to be Solved by the Invention During heat welding, the sealing material flows to the inside and outside of the battery due to the softening of the resin and the pressure applied, and the wall becomes thinner, so the outer dimensions of the sealing part are reduced due to the resin protruding. It becomes irregular and large. In addition, the opposing positive and negative terminal plates are formed by punching a thin metal plate such as stainless steel, and due to slight deformation of the edges such as burrs during the punching process, the ends of the terminal plates come into contact with each other, causing the battery Short circuits were likely to occur.

Problems such as deformation of the outer periphery of the battery and short circuits in the battery are caused by the fact that the sealing material has a tendency to become deformed due to poor mechanical strength during heat welding. There was a problem in that the sealing material did not have both strength and strength.

The present invention solves the above-mentioned conventional problems and provides a flat battery with a stable external shape, no risk of short circuit as a battery, good sealing performance, and stable quality. This is the purpose.

Means for Solving the Problem In order to solve this problem, the present invention includes at least one unit cell, a pair of opposing positive and negative metal terminal plates, and an insulating member interposed between the peripheral edges thereof. In a flat battery configured by incorporating the unit cell in a battery chamber formed by heat welding with a sealing member made of solid thermoplastic resin, the sealing member is provided with a large area relative to the positive and negative terminal plates. It has a three-layer structure consisting of a base mainly made of a polyolefin resin in contact with the base, and a carboxyl group-containing polyolefin resin that has a higher melt viscosity than the base at a welding temperature and is laminated on both the inside and outside of this base.

According to this configuration, in order to weld the seal member with good sealing properties with little deformation during welding, the seal material is applied to the inside and outside of the battery with respect to the positive and negative terminal plates of the welded part. A resin layer having a high melt viscosity at the welding temperature is provided, and a resin layer having a relatively low melt viscosity is provided on the base body serving as the core of the sealing member. Therefore, the sealing performance is better than this K,
This makes it possible to seal a battery with little deformation of the sealing member, which is extremely useful for improving storage characteristics.

Embodiment FIG. 1 shows a flat battery according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a negative electrode terminal plate which also serves as a negative electrode current collector and a part of the container, and is made of stainless steel foil.

A negative electrode 2 made of lithium foil is crimped onto the inner surface of this negative electrode terminal plate. 3 is a separator made of polypropylene nonwoven fabric, 4 is a positive electrode mixture layer formed by mixing manganese dioxide, fluororesin powder, and acetylene black, rolling it to a predetermined thickness, and drying it. Configure. Reference numeral 6 denotes a positive terminal plate made of stainless steel foil and serving as a positive electrode current collector and a part of the container. A modified polyethylene sealing material 7 processed into a window frame shape is interposed between the peripheral edges of a pair of opposing negative and positive electrode terminal plates 1 and 6, and the sealing material 7 is moved between the terminal plates 1 and 6 by pressure and heating. It is welded to the periphery and seals the battery chamber containing the power generation element.

The material of the sealing member 7 is usually a resin layer 7' made of a polyolefin resin with good solvent resistance, which has a high melt viscosity at the welding temperature, and a core base 7 with a lower melt viscosity than the resin layer 7'.
It is a three-layer composite structure that is laminated on both the inside and outside of the ``.

The resin that forms the base 7" has a melting point or softening point that is usually 10 to 30'C lower than the resin laminated on both the inside and outside of the base, and can be quickly welded to the terminal board at a relatively low temperature. At the same time, it is preferable to use a product containing a calphokyl group to increase the adhesion effect to metals.For example, ethylene or propylene monomers containing acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, maleic anhydride, etc. It is obtained by copolymerizing or graft polymerizing unsaturated carboxylic acids such as acids.

On the other hand, the resin layers laminated on both the inner and outer sides of the base material serving as the core material in the positive and negative electrode directions are made of the same type of resin as the base material and have a higher melt viscosity than the base material at the bonding temperature, and are similar to the base resin. , contains a carboxyl group to increase the adhesion effect with metals.

The melt viscosity referred to here is measured at the bonding temperature using the same measurement method as the normal polyethylene melt index.
It is necessary that the resins on both sides laminated inside and outside have a density of 1.5 or less, preferably 0.6 or less, and a difference from the base resin of 1.0 or more.

Various combinations of polyolefin resins can be considered for the above-mentioned sealing member, but among them, ultra-high molecular weight polyethylene sheets with an average molecular weight of 1 million or more as determined by the viscosity method or 3 million or more as determined by the light scattering method and By using a crosslinked polyethylene sheet with a gel fraction of at least 50% or more, preferably 70% or more, as measured by hot xylene dissolution method, it is possible to effectively prevent thinning of the seal portion due to flow, and It is most preferable as a sealing member for nonaqueous electrolyte batteries because it takes advantage of the inherent inert and low moisture permeation properties of polyolefin resins.

In FIG. 1, 7 is a sealing member consisting of a polyethylene base 7'' and a resin layer 7' laminated on both the inner and outer sides of the base 7''.
% polymerized to contain carboxyl groups.

The softening point of the base 7'' is approximately 150°C, which is suitable for thermal bonding.The softening point of the resin layers 7' on both the inner and outer sides of the button laminated on the base 7 is approximately 170°C, which is higher than that of the base 7''. Made of high density polyethylene. The shape of the battery is O-50rt thick.
rm, the outer diameter is 30 x 30 mm, the thickness of the stainless steel foils 1 and 6 is 30μ, and the thickness of the sealing material base 7 is 300μ.
, the resin layers 7' on both the inner and outer sides have a thickness of 60μ. 7- in Figure 1
As is clear from looking at each seal part of the button A, in the case of the button shown in FIG. maintains a predetermined shape with almost no deformation, and the base resin layer 7
” and the terminal plate 1゜e made of stainless steel foil are reliably thermally welded. Therefore, the shape of the battery is also constant, and short circuits of the battery due to contact between the terminal plates 1 and 6 made of stainless steel foil are also prevented. Moreover, since the base body 7'', the resin 7' on both sides, and the terminal plate 1.degree. 6 are in close contact with each other, the leakage resistance and storage performance are excellent.

Next, a flat battery constructed using the above-mentioned conventional technology was
The internal resistance and leakage resistance of each sample were measured immediately after manufacture (r) and after storage at 60°C for 4 weeks (<ff), with the product according to this example designated as B, and the results are as shown in the following table. there were.

Further, FIG. 2 shows the discharge characteristics of these two types of batteries, A and B, when they were stored at 60° C. for 4 weeks, connected to a load resistance of eaKΩ, and discharged in an atmosphere of 20° C.

Effects of the Invention As detailed above, the present invention has good sealing properties by welding,
By using a sealing member that is less deformed during welding by combining and integrating polyolefin resin layers with different properties, a flat battery with good sealing performance, a constant external shape, and no short circuit is provided. It is.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a flat battery in an embodiment of the present invention;
FIG. 2 is a diagram of its discharge characteristics. 1...Negative electrode terminal plate, 2...Negative electrode, 3.
...Separator, 4...Positive electrode mixture, 6.
... Conductive coating film, 6 ... Positive terminal plate, 7
... Seal member, 7'' ... Seal member base (polyethylene), 7' ... Resin layer on both sides of seal member, 7-A ... Seal Department. Name of agent: Patent attorney Toshio Nakao and one other person”'
---4 goods 1 Figure 2 Special m! rM(ar)

Claims (1)

[Claims] A flat battery chamber that houses a power generation element in a battery chamber formed by thermally bonding a window frame-shaped sealing member made of thermoplastic resin that also serves as an insulating member to the periphery of the battery containers of the opposing positive and negative electrodes. type battery, wherein the sealing member heats a base body mainly made of a polyolefin resin, and resin layers mainly made of a carboxyl group-containing polyolefin resin having a melting temperature higher than that of the base body on both the inner and outer sides of the base body. A flat battery that is laminated and integrated by fusion bonding.