JPH0744038B2 - Sealed secondary battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention realizes a sealed secondary battery, and more specifically, realizes a thinner battery with device miniaturization, and further has a long life and high reliability. The present invention relates to a hermetically sealed secondary battery capable of simultaneously achieving the same, and particularly to a film substrate used for the hermetically sealed secondary battery.

(Prior Art) With the spread of small devices such as portable devices, the demand for inexpensive and thin sealed secondary batteries is increasing. As a method of reducing the thickness, for example, Japanese Patent Application No. 63-185085 (Japanese Patent Application Laid-Open No.
132064), there is a sealed secondary battery.

In this battery, a positive electrode plate and a negative electrode plate are juxtaposed on the same plane of a film substrate made of plastic, and a space between each end face of the positive electrode plate and the negative electrode plate is filled with an electrolyte containing sulfuric acid.

By adopting this structure, the method of advancing the field of the battery reaction due to charge / discharge is not the reaction between the electrode surfaces but the reaction between the electrode end surfaces in the direction parallel to the electrode surfaces. This protects the current collector located at the center of the electrode surface against deterioration, and thus enables the battery to be thinned without reducing the battery life even if the electrode becomes thin.

As a film substrate on which the electrode plates of this battery are arranged side by side, a polyolefin resin film such as polyethylene or polypropylene which is an acid resistant polymer is used. The film substrate also serves as a battery case, the same film substrate as the film substrate is provided on the upper surface, and the upper and lower film substrates are heat-sealed at their outer circumferences except for the safety valve portion to form a hermetically sealed structure. It enables excellent manufacturability, reliability, and weight reduction.

(Problems to be solved by the invention) However, if the electrode plate is thickened in order to increase the capacity while maintaining the thin shape of the battery shape of about 1 mm, the film substrate must be thinned. Therefore, there is a problem that (i) the strength of the battery case against bending is insufficient, and (ii) the amount of moisture in the electrolyte that permeates the outside of the battery case is large, so that the battery capacity is reduced, that is, the battery life is shortened. Have a point.

The present invention has been made in view of the above-mentioned problems, and a new sealed secondary battery capable of improving the strength of the battery case and extending the battery life without deteriorating the battery shape feature of the thin battery. In particular to provide a film substrate.

(Means for Solving the Problems) In order to solve the above problems, in the sealed secondary battery according to the present invention, the positive electrode plate and the negative electrode plate are arranged on the same plane of the first film substrate, and the positive electrode An electrolyte is filled in a gap between the plate and the negative electrode plate, and a second film substrate which is the same as the first film substrate is arranged on the upper surface of the first film substrate so as to cover the positive electrode plate, the negative electrode plate and the electrolyte. In the sealed secondary battery in which the outer peripheries of the first and second film substrates are heat-sealed to form a sealed structure, the first and second film substrates have a water vapor transmission rate of 0.08604 g / m ² , 24h, 40
The film is characterized by being a single-layer film or a multi-layered film having moisture resistance at 90 ° C. and 90% RH or less and strength as a battery case.

That is, the film substrate constituting the sealed secondary battery has a moisture permeability of 0.08604 g / m ² , 24 h, 40 ° C., a single layer film or a multilayer structure satisfying the moisture resistance of 90% RH or less and the strength as a battery case. The main feature is that it is a film.

Also, for the purpose of making the sealed secondary battery thinner, the thickness of the film substrate is 125 μm or less, and the water vapor transmission rate is 0.08604 g /
It is also characterized by having moisture resistance of m ² , 24h, 40 ℃, 90% RH or less and strength performance as a battery case.

Furthermore, when a multi-layered film is used as the film substrate, the film structure is composed of at least a heat-sealable adhesive layer, a moisture-proof layer for preventing moisture in the electrolyte from escaping outside the battery cell, and a reinforcing layer. The protective layer has a three-layer structure, and the moisture-proof layer and the protective layer are formed on the upper surface of the adhesive layer in a forward / reverse manner.

(Structural Example) FIG. 1 shows a structure of a sealed secondary battery using a three-layer structure film as an example using a multilayer structure film among the film substrates used in the sealed secondary battery of the present invention.
In the figure, (a) is a plan view, (b) is a cross-sectional view taken along the line AA ′ in the outer peripheral portion of the heat-sealed film substrate, 1 is a positive electrode plate, 2 is a negative electrode plate, 3 is an electrolyte, and 4 is a film. Substrate, 5
Is a safety valve, 6 is an adhesive layer, 7 is a moisture-proof layer, and 8 is a protective layer.

As is apparent from FIG. 1 described above, in the sealed secondary battery according to the present invention, the positive electrode plate 1 and the negative electrode plate 2 are formed on the same plane of the first plastic substrate 4, and the electrolyte 3 is provided on the positive electrode plate. 1 and the negative electrode plate 2 were filled in a space (see FIG. 1 (a)), and a second plastic substrate 4'was arranged so as to cover the positive electrode plate 1, the negative electrode plate 2 and the electrolyte 3. It has a structure (see FIG. 1 (b)). 5
Is a safety valve.

Here, the film substrates 4 and 4'having a three-layer structure are composed of the adhesive layer 6,
The positive electrode plate 1 is composed of a moisture-proof layer 7 and a protective layer 8.
The negative electrode plate 2 is fixed on the adhesive layer 6 by thermocompression bonding, and the electrolyte 3 containing sulfuric acid is further formed between the positive electrode and the negative electrode.

In the case of forming a sealed secondary battery, a film substrate 4 having the same structure as the film substrate 4 is arranged on the upper surface of the film substrate 4 so as to cover the positive electrode plate 1, the negative electrode plate 2 and the electrolyte 3, and the upper and lower films are formed. It is realized by heat-sealing the adhesive layers 6 of the substrates 4 at their outer peripheral portions.

The material used for the adhesive layer 6 is a polyolefin resin such as polyethylene or polypropylene, or ethylene.
Polyolefin hot melt adhesives such as acrylic acid / maleic anhydride terpolymers and polypropylene adhesives are available. When a polyolefin resin is used for the adhesive layer 6, it is necessary to previously coat the adhesive surfaces of the positive electrode plate 1 and the negative electrode plate 2 with the same polyolefin resin film. On the other hand, when a hot melt adhesive is used for the adhesive layer 6, the above-mentioned polyolefin resin film coating is not necessarily required on the adhesive surfaces of the positive electrode plate 1 and the negative electrode plate 2. Therefore, there is an advantage that the capacity of the battery can be further increased by increasing the amount of the active material of the electrode plate material corresponding to the thickness. Further, the thickness of the adhesive layer 6 is required to be at least 30 μm from the viewpoint of ensuring reliability when heat sealing the outer peripheral portion.

Next, the function of the moisture-proof layer 7 will be described.

When water in the electrolyte escapes to the outside of the battery cell, the battery capacity deteriorates with time. 80 to the initial battery capacity
%, The moisture permeability of the film substrate should be 0.08604g / m ² , 24h, 40h in order to maintain a life capacity of at least 5 years.
℃, 90% RH or less is required. For the calculation of the moisture vapor transmission rate, refer to the report “Abstracts of the 85th Autumn Meeting of the Electrochemical Society of Japan,” P83.
(1985) ”, based on the theoretical consideration of battery life, the time until the battery capacity drops below 80% (reduced water content 28 wt%) is defined as the battery life. About.

In addition, when aiming to make the sealed secondary battery thinner,
The thickness of the film substrate 4 needs to be 125 μm or less in order not to impair the thin battery feature. In such a case, the film substrate thickness should satisfy the above moisture permeability. It is necessary to select a suitable material for the film substrate 4. For example, if a material such as polychlorotrifluoroethylene having a thickness of 50 μm, aluminum having a thickness of 30 μm, or a titanium alloy is used as the moisture-proof layer 7, the moisture permeability of the film substrate 4 is 0.08604 g / m ² , 24 h, 40 ° C., 90 It can be less than or equal to% RH.

Further, the moisture permeation rate of water from the heat-sealed portion in the outer peripheral portion of the adhesive layer 6 also needs to satisfy the moisture vapor transmission condition, but in the case of the adhesive layer 6 using a normal polyolefin resin,
If the heat-sealing width of the adhesive layer 6 is about 2 mm or more, the moisture permeability condition can be sufficiently satisfied.

Further, the protective layer 8 is preferably made of a material having a higher strength than the material used for the adhesive layer 6, such as a heat resistant resin such as polyimide or polyethylene terephthalate.
Examples include highly crystalline polypropylene and fiber reinforced plastics.

FIG. 2 shows another example of the structure of the film substrate used in the sealed secondary battery of the present invention, which is different from FIG. 1 (b) in that the protective layer 8 is on the inside and the moisture-proof layer 7 is on the outside. The points are different. In the case of such a structure of the film substrate 4,
If aluminum is used as the moisture-proof layer 7, the aluminum surface can also serve as the terminal of the electrode. That is, by fixing the terminals of the positive electrode plate 1 to the upper surface moisture-proof layer 7 and the terminals of the negative electrode plate 2 to the lower surface moisture-proof layer 7, the aluminum surface can be used as the electrode terminal surface. As a result, the thin battery and the device to be used have a feature in that they are convenient in terms of design in terms of adhesion.

Next, examples for confirming the performance of the film substrate having a three-layer structure according to the present invention shown in FIGS. 1 (b) and 2 will be shown below.

(Example) An adhesive layer 6, a moisture-proof layer 7, and a protective layer 8 were laminated by a film laminator in a three-layer structure shown in FIGS. 1 (b) and 2 to form a laminated film, which was used to form a hermetically sealed type film. The next battery was created. An example of the construction of the film substrate is shown in Table 1. Examples 1 to 7 have the construction shown in FIG. 1 (b), and Examples 8 to 11 have the construction shown in FIG.

The size of the created battery is 54 mm in length, 85 mm in width, and 1 mm in thickness, and the initial capacity of this battery is about 70 in all the examples.
It was mAh.

Using this battery, 40 ℃, 2.45V constant voltage, maximum charging current
Trickle charging was performed under the condition of 0.25C, and the capacity test was conducted every 30 days under the condition of the discharge current of 0.25C and the discharge end voltage of 1.7V. The results of the capacity change up to 150 days after the initial capacity are shown in Table 1, and the time-dependent capacity change is shown in FIG. In addition,
The environmental water vapor pressure of the battery under trickle charging was set to 14 mmHg.

(Comparative Example) A sealed secondary battery was prepared in the same manner as in Example except that a polypropylene film having a thickness of 100 μm was used as the film substrate. The results of a capacity test conducted on this battery in the same manner as in the example are shown in Table 1, and the change in capacity with time is shown in FIG.

As shown in Table 1 and FIG. 3, when a sealed secondary battery is constructed by using the three-layer structure film of the present invention as a film substrate, a material that does not satisfy the moisture permeability condition as in Comparative Example is used. Compared to when used as a film substrate,
No reduction in capacity due to trickle charging was observed, and the strength as a battery case was sufficiently satisfied.

In addition, in this example, as a multilayer structure film,
Although an example using a layered film has been shown, it goes without saying that even in the case of a multilayered film having another structure, the same effect is produced as long as the moisture permeability condition and the strength as a battery case are satisfied. .

That is, as the multilayer structure film, the following structures are conceivable.

PET (12) / Al (20) / PET (12) (insulating layer) / PE (20) PET (12) / Al (20) / PET (12) (insulating layer) / AP (20) PET (12) / Al (20) / Polyimide (12) (insulating layer) / AP
(20) Here, PET represents polyethylene terephthalate, PE represents polyethylene, and AP represents a polypropylene adhesive, and the numbers in parentheses in the above abbreviations indicate thickness (μm) (the same applies to Table 1).

The multi-layer structure film having such a structure is effective when the thickness of the adhesive layer 6 cannot be secured, and in addition to the three-layer structure film of the present invention shown in Table 1, the adhesive layer 6 and the moisture-proof layer 7 are newly added. An insulating layer is provided between the layers to prevent short circuit between the upper and lower Al surfaces due to melting of the adhesive layer 6 during heat sealing.

When a single-layer film is used as the film substrate, a film material that satisfies the moisture vapor transmission conditions and the strength of the battery case is selected, or when a thin battery is manufactured using the single-layer film. , Thickness 12
It is necessary to select a film material having a thickness of 5 μm or less and satisfying the moisture permeability condition and the strength as a battery case.

(Effect of the invention) As described above, in the present invention, in the sealed secondary battery in which the positive and negative electrode plates are arranged on the same plane of the film substrate, the film substrate has moisture resistance and hardness as a case. Since it is a multi-layer structure film, the sealed secondary battery used for this has a longer life and protection as a case than the conventional sealed secondary battery using a film substrate with poor moisture resistance and hardness. Since the thin secondary battery is achieved at the same time, the practical industrial value of the thin secondary battery is enormous.

[Brief description of drawings]

1 (a) is a plan view of the sealed secondary battery of the present invention and FIG. 1 (b) is a sectional view taken along the line AA ', and FIG. 2 is different from FIG. 1 (b) of the present invention. Sectional views of different film substrates, third
The figure is a capacity curve in the trickle charge period of the batteries shown in Examples 1 to 11 of the present invention and Comparative Example. 1 ... Positive electrode plate, 2 ... Negative electrode plate, 3 ... Electrolyte, 4 ... Film substrate, 5 ... Safety valve, 6 ... Adhesive layer, 7 ... Moisture-proof layer, 8 ... Protective layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Maki Ishizawa 1-1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Tsutomu Ogata 1-1-6 Uchisai-cho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. A positive electrode plate and a negative electrode plate are arranged on the same plane of a first film substrate, an electrolyte is filled in a gap between the positive electrode plate and the negative electrode plate, and the upper surface of the first film substrate is aforesaid. A second film substrate, which is the same as the first film substrate, is arranged so as to cover the positive electrode plate, the negative electrode plate and the electrolyte,
In a sealed secondary battery in which the outer peripheries of the first and second film substrates are heat-sealed to form a sealed structure, the first and second film substrates have a water vapor transmission rate of 0.08604 g / m ² , 24
A sealed secondary battery, which is a single-layer film or a multi-layered film having a moisture-proof property at 40 ° C., 90% RH or less for h, and strength as a battery case. 2. The hermetically sealed secondary according to claim 1, wherein the first and second film substrates are single-layer films or multi-layered films having a thickness of 125 μm or less. battery. 3. The three-layer structure of the multi-layer structure film comprising at least a heat-sealable adhesive layer, a moisture-proof layer for preventing moisture in the electrolyte from escaping outside the battery cell, and a protective layer for reinforcing the battery case. 3. The hermetically sealed type two according to claim 1 or 2, which is made of a film and has the moisture-proof layer and the protective layer formed on the upper surface of the adhesive layer in a forward / reverse manner. Next battery.