JPH04296467A - Sealed-type battery and manufacture thereof - Google Patents

Abstract

PURPOSE:To maintain the necessary pressure to keep close adhesion between electrodes in order to elevate charging-discharging efficiency and improve the battery' s properties even if a cathode and an anode of a coiled electrode body expand and shrink owing to the charging and discharging. CONSTITUTION:An expandable polyethylene is set in the center space part and the outer circumference of a coild electrode body 1 and the resulting body is inserted into a battery container 10. The expandable polyethylene is heated in the container 10 to make foams and form volume-increased pressing materials 5' and 8'. Pressure is applied to the coild electrode body l by the volume- increased pressing materials 5' and 8' and thus the adhesion strength of the cathode 2 and the anode 4 is improved.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a sealed battery equipped with a spiral electrode body, and more particularly to a sealed battery equipped with a pressurizing material that applies appropriate pressure to the spiral electrode body. be.

0002

2. Description of the Related Art For example, in the case of a nickel-hydrogen battery, the hydrogen storage alloy serving as the negative electrode expands and contracts as the battery is charged and discharged, and in the case of a nickel-cadmium battery, the electrode active material expands and contracts as the battery discharges and charges. Therefore, a sealed battery has been proposed in which a pressurizing material is disposed in the electrode group of such a sealed battery to appropriately apply pressure between the positive and negative electrodes of the electrode group. For example, for sealed batteries with spiral electrode bodies, such as nickel-cadmium batteries, a technology has been proposed in which the outermost periphery of the electrode group is fixed with adhesive tape to maintain a uniform distance between the positive and negative electrodes. has been done (
(Japanese Unexamined Patent Publication No. 60-170171). However, although this technique using tape is effective in maintaining adhesion between the electrode parts closer to the outer periphery of the electrode group, there is a problem in that the winding pressure is relaxed between the electrode parts closer to the center of the electrode group. be. In addition, although the tape itself does not deteriorate significantly, if the adhesive applied to the tape deteriorates due to the electrolyte and expansion and contraction during charging and discharging, the binding force of the tape decreases, causing the electrodes from the outer periphery of the electrode group to deteriorate. There is also a problem in that the adhesion between the parts also decreases. Furthermore, since this technology makes use of the stress generated during winding to bring the electrodes into close contact, depending on the material of the electrodes, the electrodes near the center of the electrode group and the electrodes near the outer periphery may experience less stress during winding. Not only will there be a difference in pressure, but there will also be a difference in the adhesion between the electrodes after winding. For example, if an electrode has a high bending strength and a low elastic modulus, the stress applied during winding will be greater near the center of the electrode group, causing the active material to peel off from the electrode base, and the winding machine When the shaft center is pulled out from the electrode group, the close contact between the electrode portions near the center of the electrodes deteriorates. As a technique for solving the above-mentioned drawbacks, as shown in Japanese Patent Application Laid-Open No. 1-227363,
(1) A water-absorbing polymer (vinyl acrylate alcohol copolymer, etc.) that expands in volume by absorbing water is placed as a pressure material in the center of the electrode group and/or its outer periphery. technology that improves the adhesion between electrodes by expanding them with an electrolyte and pressurizing the electrode group, and (2)
) A technique has been proposed in which a shape memory alloy or shape memory resin is placed as a pressurizing material in the same area as above, and this is heated to transform the shape memory alloy or shape memory resin, thereby pressurizing the electrode group. .

0003

[Problem to be solved by the invention] However, the above (1)
) and (2) above have the following problems in production or in the finished battery. [A] Problems when using a water-absorbing polymer as a pressurizing material (a) In order for a water-absorbing polymer to expand in volume, it must absorb enough electrolyte to expand; This means that an amount of electrolyte will be injected. As a result, the weight of the water-absorbing polymer serving as the pressurizing material and the absorbed electrolyte are added to the weight of the conventional battery, resulting in a problem that the weight of the battery increases. (b) When injecting electrolyte, the water-absorbing polymer that serves as the pressurizing material is expanded; however, if the electrolyte is injected before the battery can is sealed, the water-absorbing polymer will expand from the opening of the battery can during injection. Because the liquid overflows, the liquid injection operation must be performed after sealing or after providing an inner lid inside the battery can. However, in order to enable liquid injection after sealing, precision machining of the can lid is required, and if an inner lid is used, there is a problem in that the weight of the battery increases by the weight of the inner lid. (c) The water-absorbing polymer expands as much as possible until its expansion force is suppressed by external pressure, and when the equilibrium pressure is reached, it no longer absorbs the electrolyte. Furthermore, water-absorbing polymers have a faster absorption rate than separators (polypropylene, nylon, etc.). Therefore, after absorbing the electrolyte necessary for expansion, the separator absorbs the electrolyte necessary for battery reaction. Usually, the pressure applied to the wound electrode group varies depending on the mechanical properties of the electrode. Therefore, even if the same water-absorbing polymer is used, its expansion rate differs for each electrode group, and the amount of electrolyte required for expansion also differs, so the amount of electrolyte injected must be changed for each battery. A problem arises. Additionally, as the charge/discharge cycle of the battery progresses and the degree of expansion and contraction of the electrodes increases, the amount of electrolyte retained in the water-absorbing polymer changes, and the amount of electrolyte retained in the separator changes accordingly, which affects battery performance. The problem of receiving arises.

[B] Problems when using a shape memory alloy or shape memory resin as a pressure material (d) When a shape memory alloy is used as a pressure material, the above (b)
Although the problems of ) and (c) are eliminated, since a metal with a large specific gravity is used, there is a problem that the weight of the battery increases more significantly than when a water-absorbing polymer is used.

(e) With pressurizing materials such as shape memory alloys or shape memory resins that do not increase in volume but change in shape upon heating to generate pressurizing force, it is difficult to apply uniform pressure to the electrode group. Then, a problem arises in that the structure of the pressurizing material becomes complicated.

(f) When a shape memory alloy or a shape memory resin is used as a pressure material, the necessary pressure can be obtained if the pressure material is heated above its transformation point. However, when charging and discharging the battery repeatedly when the ambient temperature is below the transformation point, the pressurizing material does not undergo the necessary deformation for pressurization.
There is a problem in that the shape memory alloy or shape memory resin that is the pressurizing material also deforms in response to changes in the volume of the electrodes as the battery charges and discharges, making it impossible to obtain the pressure necessary for close contact between the electrodes.

[0007] An object of the present invention is to provide a sealed battery that can maintain the pressure necessary for close contact between electrodes regardless of the ambient temperature.

Another object of the present invention is to provide a sealed battery that can easily and reliably arrange a pressurizing material without increasing the weight of the battery as much as possible and without increasing the amount of electrolyte, and a method for manufacturing the same. It is about providing.

Still another object of the present invention is to provide a method for manufacturing a sealed battery that can simplify the battery assembly process.

0010

[Means for Solving the Problems] In order to solve the above problems, the invention according to claim 1 provides a spiral electrode body in which an electrode is spirally wound with a separator interposed between a positive electrode and a negative electrode. In a sealed battery stored in a battery container,
A pressurizing material whose volume has irreversibly increased due to physical change is disposed in at least one of the central space of the spiral electrode body and the outer peripheral space between the outer peripheral surface of the spiral electrode group and the battery container.

[0011] In the specification of this application, "physical change" does not mean causing a change in a substance by filling or adding a chemical substance such as an electrolytic solution, but rather refers to applying physical energy such as heat or vibration. It means to cause a change in a substance by doing something.

[0012] In the second aspect of the invention, the pressurizing material is made of a foamed material that is foamed by physical change to form a closed cell structure inside.

In the third aspect of the invention, a pressurizing material whose volume increases due to a physical change and exhibits an irreversible change is disposed in at least one of the central space of the spiral electrode body and the outer circumference of the spiral electrode body. After the assembly is made and the electrode assembly is housed in a battery container, a physical change is applied to the pressurizing material.

[0014]

[Operation] In the invention of claim 1, since the pressurizing material whose volume has irreversibly increased due to a physical change is used, the volume of the pressurizing material is substantially changed due to changes in ambient temperature, etc. after the volume has increased. There isn't. Therefore, unlike shape memory alloys and shape memory resins, the shape does not change depending on the ambient temperature, and the necessary pressure can be applied between the electrodes without being affected by the ambient temperature. can improve sex.

[0015] According to the second aspect of the invention, if a foam material that expands due to physical change to increase the volume and forms a closed cell structure inside is used as the pressurizing material that irreversibly increases the volume, the battery can be improved. The necessary pressurizing force can be obtained without significantly increasing the weight of the pressurizing material, and without increasing the amount of electrolyte as in the case of pressurizing materials made of water-absorbing polymers. The closed cell structure imparts elasticity to the pressurizing material, so it is possible to maintain the pressure necessary to maintain close contact between the electrodes even after repeated charging and discharging. Even if the adhesion state is uneven, the adhesion state can be made uniform.

[0016] According to the third aspect of the present invention, an electrode assembly is produced in which a pressurizing material is disposed in at least one of the central space of the spiral electrode body and the outer circumference of the spiral electrode body, and the electrode assembly is used in a battery. If the pressurizing material is subjected to a physical change after being stored in the battery container, it is easy to place the pressurizing material in the battery container, and
The pressurizing material can be placed in a predetermined location without causing liquid leakage and without requiring an inner lid or the like, and the battery assembly process can be simplified.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a sectional view of an embodiment in which the present invention is applied to a nickel-metal hydride battery, and FIG. 2 is a partially cutaway perspective view showing an aspect of one step of the manufacturing process. In addition, in Figure 1,
The separator 3 in the spiral electrode body 1 is not shown. Further, the spiral electrode body 1 shown in FIG. 2 is exaggerated for ease of understanding, and the number of windings is different from that of the spiral electrode body 1 in FIG. The spiral electrode body 1 is constructed by stacking and winding a positive electrode 2, a separator 3, and a negative electrode 4. The positive electrode 2 uses a 60 mesh nickel net as an electrode base, 90 wt% nickel hydroxide as an active material, 2 wt% nickel fiber as a conductive agent, 5 wt% metal cobalt as an activator for the active material, and polytetrafluoro as a binder. A solid composition of 3 wt% ethylene is used. Further, the separator 3 is made of a microporous polypropylene film. Further, the negative electrode 4 is made of MmNiMnCo (1:4.5:
A paste made by mixing and kneading a hydrogen storage alloy (0.2:0.3) and polyvinyl alcohol as a binder is mixed with foamed nickel (Celmet [trademark] manufactured by Sumitomo Electric Co., Ltd.).
It was manufactured by filling the

In this embodiment, as shown in FIG. 2, a foamed polyethylene sheet 5 having a thickness of 0.1 mm is wound around the outer peripheral surface of the spiral electrode body 1, and the end of the winding is It is fixed by partially welding one or more points to form a thermally welded part 6. When performing this partial welding, a heating iron with a width of 2 mm is attached to the electrode so that the volume expansion of the foamable polyethylene 5 due to partial heating spreads not in the electrode lamination direction of the spiral electrode body 1 but in a direction perpendicular to the electrode lamination direction. Partial welding is performed while shifting in the direction perpendicular to the stacking direction. In this example, a sheet-like foamable polyethylene manufactured by Nitto Electric Industry Co., Ltd. that can be expanded to three times its size is used. Currently commercially available foamable polyethylene has a volume that increases by 2 to 12 times before heating due to foaming, and the stress at this time is 0.5 kgf/cm2 to 10 kgf/cm.
2 is shown. As an example, the specific gravity of expandable polyethylene before foaming is 0.93, which is lighter than the electrolyte (specific gravity of 1.2 to 1.4 for nickel-cadmium batteries), so the weight of the battery can be significantly reduced. It will not increase. Further, a round rod-shaped foamed polyethylene 8 having a diameter of 3 mm and expanded 10 times is inserted into the central space 7 of the spiral electrode body 1. The round rod-shaped foamed polyethylene 8 is inserted into the central space 7 from the opposite side at the same time as the shaft core 9 of the winding machine is pulled out. In this way, the foamed polyethylenes 5 and 8 constituting the pressurizing material before volume increase are attached to the spiral electrode body 1 to form an electrode assembly.

The electrode assembly manufactured in this way is housed inside the battery container 10, and heated at 120° C. for 10 minutes with the battery container 10 open to form foamed polyethylene 5,
By foaming 8, pressurizing materials 5' and 8' with increased volumes are formed. The pressurizing member 5' whose volume has increased is disposed in a restrained state in the outer circumferential space between the outer circumferential surface of the spiral electrode body 1 and the inner circumferential surface of the battery container 10. Since the spiral electrode body 1 is pressurized from both inside and outside by the pressure members 5' and 8' whose volumes have increased, the positive electrode 2 and the negative electrode 4 are brought into close contact with each other with the separator 3 in between. After that, an electrolytic solution (30% potassium hydroxide aqueous solution) is poured, and then the current collector 11 is welded to the end of the positive electrode 2 and the battery lid 12, and the battery lid 12 is fixed by drawing and caulking. to seal the battery container 10. In FIG. 1, 13 is a pressure relief valve.

FIG. 3 shows the nickel-hydrogen battery A of the above embodiment.
and shows the cycle characteristics of conventional battery B. Conventional batteries are
Water-absorbing polymer (vinyl alcohol acrylate) for pressure material
The battery is the same as the battery in the above example except that . As the number of cycles increases, a difference occurs in battery capacity between conventional battery B and battery A of the present invention.
Hydrogen battery A showed no decrease in capacity up to 600 cycles. In addition, in the battery A of the present invention, the adhesion between the electrodes was better than in the conventional battery B, so the battery capacity was also increased. Furthermore, the weight of conventional battery B is 24.7g for AA size.
However, in contrast, battery A of the present invention weighed 23.4g.
Therefore, the weight was reduced by 1.3g.

According to this embodiment, even if the volume of the pressurizing material increases, there is no large increase in weight, and the increase in weight can be reduced compared to conventional batteries. In addition, since the pressurizing material is made of foamed polyethylene that irreversibly increases in volume, the pressurizing material after increasing in volume becomes an elastic body with a closed cell structure inside.
Even after repeated charging and discharging, the pressure required to maintain close contact between the electrodes can be maintained. Further, since the volume increase of the pressurizing material is due to heating, there is no change in the amount of electrolyte held in the separator due to a change in the volume of the pressurizing material, unlike in the case of using a water-absorbing polymer. Furthermore, since the pressure material itself increases in volume (foams) by simply heating, the battery assembly process and its internal structure can be simplified. In addition, even if the mechanical properties of the electrodes are different and the adhesion between the electrodes in the electrode group is uneven, the adhesion can be made uniform because the pressurizing material is a foam with elasticity. . The present invention is not limited to the above-mentioned nickel-hydrogen batteries and nickel-cadmium batteries, but also applies to various batteries whose electrodes expand and contract during charging and discharging.
Effective in maintaining adhesion between electrodes. Even when applying the present invention to other batteries, if a pressurizing material whose volume increases when heated is used, it is necessary to select a separator that does not lose its properties even when heated. In addition, the material constituting the pressurizing material used in the present invention is not limited to the above-mentioned foamed polyethylene, but also any material that shows irreversible volume increase due to physical changes such as heating or ultrasonic vibration, and is resistant to electrolyte. Any material can be used.

[0022]Also, in the above embodiment, the pressurizing material is placed in both the center space and the outer circumference of the spiral electrode body. It can also be applied when the pressurizing material is placed only on one side. When the pressurizing material is disposed only in the central space, it is preferable to make the inner diameter of the battery container and the outer diameter of the spiral electrode body as close as possible. In addition, when a pressurizing material is placed only on the outer periphery of the spiral electrode body, the spiral electrode body is formed so that the diameter of the central space is as small as possible, or an appropriate insulating material is placed in the central space. All you have to do is fill it up.

[0023]

According to the invention as claimed in claim 1, since the pressurizing material whose volume has irreversibly increased due to physical change is used, the pressurizing material whose volume has increased is substantially reduced in volume due to changes in ambient temperature, etc. It does not change, and has the advantage that the necessary pressing force can be applied between the electrodes without being affected by the ambient temperature, and the adhesion between the electrodes can be improved.

According to the second aspect of the invention, the pressurizing material is made of a foaming material that expands due to physical changes to increase its volume and form a closed cell structure inside, so that the weight of the battery can be significantly increased. Moreover, it has the advantage that the necessary pressurizing force can be obtained without increasing the amount of electrolyte as is the case with pressurizing materials made of water-absorbing polymers. In addition, the closed cell structure imparts elasticity to the pressurizing material, so it is possible to maintain the pressure necessary for adhesion between the electrodes even after repeated charging and discharging. Even if it is non-uniform, there is an advantage that the adhesion state can be made uniform.

According to the third aspect of the present invention, an electrode assembly is produced in which a pressurizing material is disposed in at least one of the central space of the spiral electrode body and the outer circumference of the spiral electrode body, and the electrode assembly is placed in a battery container. In order to cause a physical change to the pressurizing material after it is stored in the battery container, it is easy to place the pressurizing material in the battery container, and
This has the advantage that the pressurizing material can be placed in a predetermined location without causing liquid leakage and without requiring an inner lid or the like, and the battery assembly process can be simplified.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a schematic structure of a nickel-hydrogen battery according to an embodiment of the present invention.

FIG. 2 is a partially cutaway perspective view showing the configuration of a spiral electrode body used in an example of the present invention.

FIG. 3 is a diagram showing the cycle characteristics of a nickel-hydrogen battery according to an embodiment of the present invention and a conventional battery.

[Explanation of symbols]

1 Spiral electrode body 2 Positive electrode 3 Separator 4 Negative electrode 5. Expandable polyethylene 5´　　Pressure material with increased volume 6 Heat welded part 7 Central space 8. Expandable polyethylene 8´ Pressure material with increased volume 9 Axial center 10 Battery container 11 Current collector 12 Battery cover 13 Pressure relief valve

Claims (3)

[Claims] 1. A sealed battery in which a spiral electrode body, which is a spirally wound electrode with a separator interposed between a positive electrode and a negative electrode, is housed in a battery container. A sealing device characterized in that a pressurizing material whose volume irreversibly increases due to physical change is disposed in at least one of the central space and the outer peripheral space between the outer peripheral surface of the spiral electrode body and the battery container. type battery. 2. The sealed battery according to claim 1, wherein the pressurizing material is made of a foam material that foams due to physical change to form a closed cell structure inside. 3. An electrode assembly is produced by arranging a pressurizing material whose volume irreversibly increases due to physical change in at least one of the central space of the spiral electrode body and the outer circumference of the spiral electrode body; A method for manufacturing a sealed battery, comprising applying a physical change to the pressurizing material after the electrode assembly is housed in a battery container.