JP2000285955A - Sealed battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin battery high in energy density by covering an electrode group where a positive electrode and a negative electrode are laminated through a separator with a thin film having a fusion surface on its inner surface, heating and crimping them to fuse the electrodes with the separator to adhere the electrode group. SOLUTION: Positive electrode 2 and negative electrode 4 which are formed by previously adhering active material to collectors are laminated through a separator 3 made of a synthetic resin to constitute an electrode group. This electrode group is covered with an armor material 1 having a fusion surface on its inner surface and heated under pressure, thereby a part of the separator 3 is melted, and is fused with the positive electrode 2 and the negative electrode 4 to integrate the electrode group. After electrolyte is injected, the armor material 1 is perfectly sealed to complete a battery. Preferably, this battery is an alkaline battery using alkaline aqueous solution as the electrolyte, and is a sealed battery where the electrode group employs lithium as the active material and nonaqueous electrolyte as the electrolyte, and the fusion temperature of thermally fused resin is lower than the hole opening temperature of the separator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for constructing a thin type sealed battery, and more particularly, to a method of forming an electrode group comprising an electrode and a separator with an exterior material having a fusion surface. In the sealed type battery.

[0002]

2. Description of the Related Art In recent years, new high-capacity secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries have been replaced with sealed lead batteries and nickel cadmium secondary batteries which have been widely used as power supplies for portable equipment for a long time. Was developed,
It has been widely used as a power source for portable devices. These batteries have increased the operating time of portable devices and increased convenience, and also made portable devices smaller and lighter.

However, in a nickel-metal hydride secondary battery, the internal pressure of the battery rises due to oxygen gas generated at the end of charging.
The battery expands. Therefore, as a preventive measure, it is used by being housed in a strong metal container. In a lithium ion secondary battery, gas is not generated during normal charge / discharge, so that the battery does not expand. However, gas is generated at the time of initial charging, and the battery expands. Although the expansion amount is small, the lithium ion secondary battery has a large liquid resistance because the electrolyte is a non-aqueous solvent, and even if the distance between the positive electrode and the negative electrode is slightly widened, the battery characteristics are extremely deteriorated. It is housed in a strong metal container like a battery and put to practical use.

In conventional use applications, the thickness of a metal container has not been a problem even with a metal container. The demand for thinner is becoming stronger. To meet this demand, metal containers having a thickness of 5 mm or less have been developed. However, the limits of cans made by narrowing down metal plates are beginning to appear.

[0005] In order to overcome the limitation of thinning of a battery housed in such a metal container, a lithium ion secondary battery will be solved by making such a thin battery completely different from the conventional one. Attempts have begun to be made. This method has two methods. One is to apply an active material to a current collector together with a gelling material, and then stack this through a separator coated with the gelling material, and then impregnate the gelling material with an electrolytic solution. The other is a polymer battery in which both electrodes are laminated via an organic solid electrolyte. However, in both cases, the method of preparing batteries, especially electrodes, is completely different from the conventional method, so that the performance is insufficient and the problem that the energy density is lower than that of the conventional battery stored in a can has become apparent. And it is not in practical use.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a battery manufacturing method which simultaneously solves the above-mentioned problem of the weight of a thin battery and the problem of the battery characteristics of a polymer battery.

[0007]

Means for Solving the Problems As a result of intensive studies on a structure for solving the above-mentioned problems, the present inventors have found that a structure in which an electrode group including an electrode and a separator is heat-pressed after forming the electrode group is very effective. We have found that there is, and have filed the present application.

The battery of the present invention is a sealed battery in which an electrode group in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween is covered with a thin film having a fusion surface on the inner surface. A sealed battery, wherein an electrode and a separator are fused to each other to bring the electrode group into close contact with each other.

It is preferable that a heat-sealing resin is previously disposed between the electrode and the separator.

Further, the electrode group uses lithium as an active material,
It is preferable that the battery uses a non-aqueous electrolyte as the electrolyte.

Further, it is preferable that the fusion temperature of the heat-fusion resin is lower than the pore closing temperature of the separator.

Further, the battery may be an alkaline battery using an alkaline aqueous solution as an electrolytic solution.

[0013] It is also preferable that the heat-fusing resin is a short fiber whose surface layer is at least made of polyethylene, and that the short fiber is sprinkled between the electrode and the separator when the electrode group is formed to form an electrode group. It is preferable from the viewpoint of the process.

When the fusion temperature of the heat-sealing resin is higher than the closing temperature of the micropores of the separator (also referred to as shutdown temperature), the electrodes are heat-fused while avoiding the closing of the micropores of the separator. In addition to this, the heat fusion strength becomes insufficient and the battery characteristics deteriorate.

There is no particular limitation on the battery configuration of such a sealed battery, and it has been widely used as well as new high-capacity secondary batteries such as nickel-metal hydride secondary batteries and lithium ion secondary batteries. The present invention is also applicable to nickel cadmium secondary batteries. Therefore, in the case of a nickel-metal hydride secondary battery, a sintered or paste-type nickel hydroxide electrode is used as a positive electrode, a LaNi5 or Laves phase hydrogen storage alloy electrode is used as a negative electrode, and a lithium ion secondary battery is used as an electrode material. For batteries, the positive electrode is LiC
oO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄
Materials such as coke, graphite, metal Li
Etc. can be used.

Also, the electrolyte is not particularly limited, and an electrolyte suitable for the above-described battery system can be appropriately selected and used. For example, in the case of a nickel-hydrogen secondary battery, an electrolyte solution containing an alkali aqueous solution such as KOH, NaOH, or LiOH alone or in a mixture is used. In the case of a lithium-ion secondary battery, an electrolytic solution such as EC, PC, MEC, DMC, or DEC is used. A solution to which a suitable amount of a supporting salt such as LiPF6 or LIBF4 is added is used. Of course, combinations other than those described here can be used as long as they can be realized as a battery system.

It is not necessary to particularly limit the selection of the separator, but it is necessary to select a material that can be fused with the exterior material. However, there is no need to select any special materials. For nickel-metal hydride secondary batteries, nylon or polypropylene non-woven fabrics, for lithium-ion secondary batteries,
A porous film of polyethylene or polypropylene may be used.

In the case of a non-aqueous electrolyte battery, the exterior material is preferably a multilayer film in which a barrier layer of aluminum or the like is inserted, but in the case of an aqueous electrolyte such as a nickel-hydrogen secondary battery, such as polypropylene. A polyolefin membrane is sufficient. Also, it is not necessary to use a special material for the material of the fusion surface, and in many cases, a polyolefin such as polyethylene or polypropylene or an ionomer can be used. (Operation) FIG. 1 shows an example of the production of the battery of the present invention. As described above, the positive electrode 2 prepared by previously adhering the active material to the current collector was used.
And a negative electrode 4 are laminated via a separator 3 made of a synthetic resin to form an electrode group. Next, this electrode group is wrapped in an exterior material having a fusion material layer on the inner surface, and heat is applied while pressing, whereby a part of the separator is melted and thermally fused with the electrode, whereby the electrode group is integrated. Although FIG. 1 shows one electrode group for each of the positive and negative electrodes, the electrode groups can be integrated by a similar method in a case where a plurality of layers are stacked or an electrode group formed by winding a long electrode.

Next, after injecting the electrolytic solution, the exterior material 1 is completely sealed to complete the battery.

With the battery having such a configuration,
Increase in battery internal pressure due to gas generated at the end of charging or initial charging makes it possible to prevent electrode spacing from expanding and battery shape from expanding, thereby suppressing deterioration of battery characteristics due to the increase in electrode spacing. It becomes possible.

That is, the electrode group formed by laminating the electrode and the separator shown in the present application is heat-pressed to integrate the electrode group without using a special electrode such as a polymer battery at all. In addition to being able to provide thin, high-energy-density lithium-ion secondary batteries, nickel-hydrogen secondary batteries and nickel-cadmium Thinning has become possible.

Further, since there is no limit in forming a can like a metal can, it is easy to prepare a battery having a thickness of 1 mm or less.
It has the feature that flexibility can be imparted to the battery.

Hereinafter, a detailed description will be given based on embodiments.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Examples) (Examples 1 to 3, Comparative Example 1) A positive electrode and a negative electrode for a nickel-metal hydride secondary battery were prepared by the following method.

Positive electrode: 90 g of nickel hydroxide and 10 g of cobalt monoxide, 0.175 g of sodium polyacrylate and 0.15 g of CMC as a kneading agent, and further 3.10 g of PTFE.
After adding 5 g and mixing well, water is added and further kneaded to prepare a nickel active material paste. Next, these pastes are rubbed on a nickel foam substrate having a three-dimensional structure (Celmet manufactured by Sumitomo Electric Industries, Ltd.), and then dried by being left in a hot air dryer. After sufficient drying, pressing was performed to a predetermined thickness using a two-stage rolling mill, and finally punching was performed to 40 mm x 60 mm by a punching press. The theoretical capacity calculated based on the nickel hydroxide content obtained from the weight of this electrode is about 1000 mAh.

Negative electrode: First, LmNi _4.0 Co _0.4 Mn
100 g of _0.3 Al _0.3, 1 g of Ketjen black,
Further, 0.1 g of CMC, 0.3 g of sodium polyacrylate, and 2 g of PTFE are added as a kneading agent and sufficiently mixed, and then water is added to prepare a hydrogen storage alloy active material paste. Next, this paste is rubbed on a nickel foam substrate (Celmet, manufactured by Sumitomo Electric Industries, Ltd.) having a three-dimensional structure in the same manner as the positive electrode, and then dried by leaving it in a hot air drier. After sufficient drying, pressing was performed to a predetermined thickness using a two-stage rolling mill.
It was punched to a size of 62 mm × 62 mm.

Then, using these electrodes, electrode groups of Comparative Example 1, Example 1, Example 2, and Example 3, which will be described in detail below, were prepared.

Comparative Example 1: The above-mentioned electrodes were laminated via a nonwoven fabric separator made of polypropylene, and the outside was covered with a laminate film having a heat-sealed surface made of an ionomer formed on the surface of a PET film. Then, the peripheral portion of the laminated film was adhered by heat fusion except for the opening for liquid injection, and then an 8N aqueous potassium hydroxide solution was injected with a syringe from the unfused portion for liquid injection, and the electrolyte was discharged. It was left until it was sufficiently absorbed by the electrode group. Thereafter, the unfused portion used for the injection was brought into close contact by heat fusion to produce a sealed battery of Comparative Example 1. FIG. 2 shows a cross section of the battery. In addition,
The heat-sealing of the laminate film was performed at 105 ° C., which is higher than the melting point of the ionomer and lower than the melting point of the polypropylene constituting the separator 23, and further, heating was performed only in the peripheral portion of the laminate film. There is no fusion of the ionomer with the ionomer. Here, 21 is an exterior material, 22 is a positive electrode, 23 is a separator,
24 is a negative electrode.

Example 1 An electrode group obtained by laminating the above-mentioned electrodes via a non-woven fabric separator made of a fiber in which a core material made of polypropylene was thinly covered with polyethylene was heat-bonded to a surface of a PET film by an ionomer. The outside was covered with the laminated film formed with. The laminate was heated to 140 ° C. while compressing the electrode group from the outer surface of the laminate film. The polyethylene in the separator was melted to fuse the separator and the electrode, and the ionomer was melted to fuse the electrode and the laminate film. Then, the peripheral portion of the laminated film was adhered by heat fusion except for the opening for liquid injection, and then an 8N aqueous potassium hydroxide solution was injected with a syringe from the unfused portion for liquid injection, and the electrolyte was discharged. It was left until it was sufficiently absorbed by the electrode group. Thereafter, the unfused portion used for the liquid injection was adhered by heat fusion to produce a sealed battery of Example 1. FIG. 3 shows a cross section of the battery. 2 are denoted by the same reference numerals, and detailed description thereof is omitted. still,
Reference numeral 30 denotes a heat-sealing layer.

Example 2 The above-mentioned electrodes were laminated via a nonwoven fabric separator made of polypropylene. At this time, lamination was performed while fine particles of polyethylene were being sprayed between the electrode and the separator. The electrode group created in this way is PET
The outside was covered with a laminate film having a heat-sealed surface made of an ionomer formed on the surface of the film. Heat to 140 ° C while pressing the electrode group from the outer surface of the laminated film, melt the polyethylene sprayed between the separator and the electrode, melt the separator and the electrode at the place where the polyethylene fine particles are scattered, and melt the ionomer and the electrode and the laminated film. Were heat-sealed. Then, the peripheral portion of the laminated film was adhered by heat fusion except for the opening for liquid injection, and then an 8N aqueous potassium hydroxide solution was injected with a syringe from the unfused portion for liquid injection, and the electrolyte was discharged. It was left until it was sufficiently absorbed by the electrode group. Thereafter, the unfused portion used for the injection was brought into close contact by heat fusion to produce a sealed battery of Example 2. FIG. 3 shows a cross section of the battery.

Example 3 The above-mentioned electrodes were laminated via a nonwoven fabric separator made of polypropylene. At this time, lamination was performed while spraying short fibers between the electrodes and the separator, the surfaces of the polypropylene core being thinly covered with polyethylene. The outside of the electrode group thus formed was covered with a laminate film having a heat-sealed surface made of an ionomer formed on the surface of a PET film. The laminate is heated to 140 ° C while compressing the electrodes from the outer surface of the laminate film.The polyethylene of short fibers sprayed between the separator and the electrode is melted to heat the separator and the electrode, and the ionomer is melted to heat the electrode and the laminate film. Fused. Then, the peripheral portion of the laminated film was adhered by heat fusion except for the opening for liquid injection, and then an 8N aqueous potassium hydroxide solution was injected with a syringe from the unfused portion for liquid injection, and the electrolyte was discharged. It was left until it was sufficiently absorbed by the electrode group. Thereafter, the unfused portion used for the liquid injection was adhered by heat fusion to produce a sealed battery of Example 3. Figure 3 shows a cross section of the battery.
Shown in

After charging these batteries at a current of 1 A for 1 hour and 20 minutes, the battery was repeatedly charged and discharged at a current of 1 A to 0.8 V, and the change in the discharge capacity with the cycle progression with respect to the initial discharge capacity was measured. FIG. 4 shows the measurement results.

As is clear from FIG. 4, the capacity of the battery of the example is small with the progress of the cycle, whereas the capacity of the battery of the comparative example is sharply reduced. When the outer shape of the battery was inspected to find out the cause, as shown in Table 1, the change in thickness of the battery of the example was small, while the battery of Comparative Example 1 was greatly expanded. all right.

From this and the results of transmission X-ray photography, the reason for the large decrease in the capacity of the battery of Comparative Example 1 was that the internal pressure of the battery increased due to the oxygen gas generated at the positive electrode at the end of charging and was fixed only in the peripheral portion It is considered that the battery of Comparative Example 1 in which the swelling of the battery was not able to be suppressed, the electrode gap was widened, and the discharge capacity was reduced. On the other hand, in each battery of the example, although the method is different, the electrode and the separator,
It is considered that since the exterior material was bonded to at least a part of the exterior material, the expansion of the battery was suppressed and the capacity reduction was small.

[Table 1] (Comparative Examples 2-3, Example 4) A positive electrode and a negative electrode for a lithium ion secondary battery were produced by the following method.

Positive electrode: A positive electrode was prepared by adding 6 g of acetylene black as a conductive material to 100 g of LiCoO ₂ , mixing well with 3 g (solid content) of PVdF and forming a paste, applying the paste to an aluminum foil, drying and pressing. This electrode was cut out to 300 mm × 50 mm and used. The theoretical capacity calculated from the amount of the active material of the positive electrode is 800 mAh.

Negative electrode: MCF1 which is a fibrous graphite
6 g (solid content) of PVdF was added to 00 g, kneaded well, and a paste was applied to a copper foil, followed by drying and pressing. This electrode is 340mm x 52m
m.

These electrodes were wound around a winding core having an outer diameter of 20 mm while insulating with a porous membrane separator made of polyethylene. At this time, lamination was performed while spraying ionomer powder having a melting point of 92 ° C. between the positive and negative electrodes and the separator. The electrode wound in this manner was removed from the winding core and crushed to form a flat electrode group. This electrode group was covered with an ionomer and an aluminum foil laminate. Then, the laminate is heated to 100 ° C. while pressing the electrode group from the outer surface of the laminate film, and the ionomer between the electrode group and the inner surface of the laminate film is thermally fused between the separator and the electrode. The part was heat-sealed in accordance with the periphery of the electrode except for a place for liquid injection. Thereafter, a solution obtained by dissolving 1 mol of LiPF6 in a mixture of equal amounts of ethylene carbonate and methyl ethyl carbonate was injected with a syringe from an injection portion on the outer peripheral portion as an electrolytic solution, and the injection hole was thermally fused. I blocked it. This battery is referred to as Example 4.

A battery prepared in exactly the same procedure as in Example 4 except that the ionomer powder was not sprayed is referred to as Comparative Example 2.

A battery in which polyethylene powder was sprayed instead of the ionomer powder of Example 4 and the heat fusion temperature was 140 ° C., which is higher than the melting point of polyethylene, is referred to as Comparative Example 3.

These were charged at a constant current up to 4.2 V at a current of 400 mA, and then charged at a constant voltage after reaching 4.2 V for a total of 5 times.
After performing the test for a period of time, a cycle of discharging to 3 V at 800 mA was repeated, and a change in discharge capacity with progress of the cycle was measured. The result is shown in FIG.

FIG. 5 shows that little deterioration was observed in the battery of Example 4 in which the electrode and the separator were heat-sealed with the ionomer powder, but rapid deterioration occurred in Comparative Example 2 in which no heat-sealing was performed. It can be seen that no capacity was obtained from the beginning of the cycle in Comparative Example 3 in which thermal fusion was performed with polyethylene powder. In order to investigate the cause, the battery after the cycle was disassembled and observed. As a result, in the battery of Example 4, the electrode group was integrated and the positive and negative electrodes were in close contact with each other. Many discharges and precipitation of the remaining metallic lithium were observed. From this, in Comparative Example 2 in which no fusion was performed, the electrode spacing was widened with the progress of the charge / discharge cycle, the current distribution became nonuniform, and metal lithium was precipitated. As a result, the capacity was reduced with the progress of the cycle. It is thought that it was.

In Comparative Example 3, the electrode group was firmly integrated as in the embodiment because heat fusion was performed with polyethylene powder, but the impedance was extremely high as a result of the impedance measurement of the battery. Was confirmed. Thereafter, the battery was forcibly disassembled and the separator was observed with a scanning electron microscope. As a result, it was found that almost all the fine holes provided in the separator had been contracted and closed. For this reason, in the battery of Comparative Example 3, polyethylene powder was used for heat fusion, and the fusion temperature was increased to 140 ° C., so that the shutdown mechanism, which is a safety mechanism of the separator, acted to close the pores, resulting in ion migration. It was considered that the battery did not function as a battery.

This indicates that it is necessary to select a heat-sealing resin to be used for heat-sealing at a temperature lower than the closing temperature of the separator.

[0044]

The present invention finds a simple and effective battery construction method in which the electrode and the separator are heat-sealed to each other. In addition to being able to provide high lithium-ion secondary batteries, it is also possible to make nickel-metal hydride secondary batteries and nickel cadmium secondary batteries thinner, which were practically impossible only with metal cans. Was.

Further, since there is no limit in forming a can like a metal can, it is easy to produce a battery having a thickness of 1 mm or less, and its industrial contribution is significant.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of the present invention.

FIG. 2 is a cross-sectional view of a part of the battery of Comparative Example 1.

FIG. 3 is a cross-sectional view of a part of the batteries of Examples 1 to 3.

FIG. 4 is a charge / discharge cycle characteristic diagram of the batteries of Examples 1 to 3 and Comparative Example 1.

FIG. 5 is a charge / discharge cycle characteristic diagram of the batteries of Example 4 and Comparative Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exterior material 2 Positive electrode 3 Separator 4 Negative electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takahisa Osaki 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Pref. F-term in Toshiba Kawasaki Office (reference) 5H028 AA01 AA07 BB04 BB05 CC02 EE06 HH08 5H029 AL07 AL12 AM01 BJ04 CJ02 CJ03 EJ12 HJ14

Claims (6)

[Claims] In a sealed battery in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween with a thin film having a fusion surface on an inner surface, the electrode group is formed by applying heat and pressure after forming the electrode group. A sealed battery, wherein the separators are fused to each other at least in a part thereof. 2. The battery according to claim 1, wherein the battery is an alkaline battery using an alkaline aqueous solution as an electrolyte.
A sealed battery according to claim 1. 3. The sealed battery according to claim 1, wherein an electrode group in which a heat-sealing resin is disposed between the electrode and the separator in advance is used. 4. The sealed battery according to claim 3, wherein the electrode group uses lithium as an active material and a non-aqueous electrolyte is used as an electrolyte. 5. The sealed battery according to claim 4, wherein a fusion temperature of the heat fusion resin is lower than a pore closing temperature of the separator. 6. The heat-fusing resin is a short fiber of which at least the surface layer is made of polyethylene, and the short fiber is formed between the electrode and the separator when forming the electrode group to form an electrode group. The sealed battery according to claim 3.