JPH1055795A - Rectangular secondary battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent short-circuit of a rectangular secondary battery in which at least one of positive and negative poles is stored in a separator made of olefin material fusion worked in a bag shape even if quick charging and discharging or shock is repeated by fusing the separator so that a fusion worked part of the separator becomes transparent. SOLUTION: For negative and positive electrode base bodies, a copper foil of 15 micrometers in thickness and an aluminum foil of 15 micrometers in thickness are employed respectively. The copper and aluminum foils are employed respectively for the negative and positive electrode base bodies. Here, a positive electrode 1 is constituted so as to be stored in a bag-shaped separator 3, a fine hole film made of polyethylene material of 25 micrometers in thickness, for example, is bent in a U shape, the positive electrode 1 is covered, and both sides bend in the U shape is thermally fused. When alignment faces for fusion is heated so as to be melted each other, a fusion part of a white separator becomes transparent. A rectangular battery is fabricated in combination with the positive and negative electrodes 1 and 2 inserted into the bag-shaped separator 3 thus fused. A battery group is housed in the rectangular metal container, and an electrolyte is injected and sealed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prismatic secondary battery comprising a large number of electrode groups and a method of manufacturing the same.

[0002]

2. Description of the Related Art As square secondary batteries, for example, small secondary batteries such as nickel-cadmium batteries and nickel-hydrogen batteries or lead storage batteries are practical techniques. Looking at the usage of separators in these,
For nickel-cadmium and nickel-hydrogen batteries,
Since the battery has a small size and a small capacity, and the strength of the electrode itself is sufficient, the separator is only slightly larger than the electrode between the positive electrode and the negative electrode. on the other hand,
Some lead-acid batteries are also known to use a mechanically crimped bag-shaped separator (JP-A-7-3026).
No. 16). Further, recently developed rocking chair type lithium secondary batteries have thin electrodes, and a rectangular sealed secondary battery in which a large number of electrodes are stacked uses a bag-shaped separator to avoid a short circuit between the electrodes. It has been proposed. Incidentally, in these bag-shaped separators, the base separator film is generally not a non-woven fabric but a microporous membrane.

[0003]

The rocking chair type lithium secondary battery described in the above prior art does not clearly define the processing technology of the separator processed into a bag shape, so that it is practically sufficient. No strong fixing strength or durability is guaranteed. A problem to be solved by the present invention is to clarify a processing technique that is unclear in the above-described conventional technique in a technique of processing a separator in a bag shape.

[0004]

Means for Solving the Problems To solve the above problems, a positive electrode 1 having a positive electrode active material mixture layer formed on an electrode substrate according to the present invention, and a negative electrode active material mixture layer formed on an electrode substrate. Negative electrode 1 and a separator interposed between these two electrodes
Battery and a battery element made of an electrolytic solution distributed over the three members are housed in a square airtight container, and at least one of the positive electrode 1 and the negative electrode 2 is formed by welding a polyolefin-based material. A structure in which the bag-shaped separator is housed in the bag-shaped separator 3 and the welded portion 4 of the bag-shaped separator.
Is transparent. The fact that the welded portion 4 of the bag-shaped separator becomes transparent means that the welded portion has been sufficiently welded, thereby ensuring practically sufficient fixing strength or durability. Also, being transparent has the advantage that it is easy to find defects in the processing operation. That is, after welding, it is easy to inspect visually or by light transmittance. In carrying out the present invention, a predetermined part of the welded portion 4 of the bag-shaped separator may be left unwelded.
In this case, by doing so, there is an effect that the penetration of the electrolytic solution into the electrodes is promoted and a short circuit between the electrodes is prevented. Specific examples of the polyolefin-based material of the bag-like separator 3 are polyethylene, polypropylene or a coexisting material thereof, and are microporous membranes which have become white and opaque by stretching or the like. In order to weld the separator into a bag shape, a method such as heating, compression bonding, or a combination of heating and compression bonding is particularly suitable. In addition,
The object of the present invention is achieved whether the electrode inserted into the bag-shaped separator is a positive electrode, a negative electrode, or both a positive electrode and a negative electrode.

As a method of manufacturing the electrodes housed in the bag-like separator 3, a bag-like separator 3 having the above-mentioned welded portion 4 is prepared in advance, and then the positive electrode or the negative electrode or both the positive electrode and the negative electrode are stored. A method is conceivable. Further, a method is also conceivable in which the separator film is bent in a U-shape to wrap the electrodes, and both sides of the U-shape are welded. However, the invention is not limited to these.

[0006]

EXAMPLE The present invention was carried out in a rocking chair type prismatic lithium secondary battery using a carbon-based material for the negative electrode.
The present invention will be described in more detail with reference to the drawings. In FIG. 2, reference numeral 1 denotes a positive electrode and 2 denotes a negative electrode. In this case, the positive electrode 1 is in a state of being inserted into a bag-shaped separator 3 to form a square electrode group. The gist of the present invention resides in the bag-shaped separator 3 and the object of the present invention is achieved by making this structure appropriate. Hereinafter, the present invention will be described in more detail with reference to specific examples and comparative examples. (Example) The electrode shown in FIG. 2 was produced as follows. A copper foil having a thickness of 15 μm was used for the negative electrode substrate, and an aluminum foil having a thickness of 15 μm was used for the positive electrode substrate. A slurry of artificial graphite powder having an average particle size of 6 μm was applied to the negative electrode substrate. N-methylpyrrolidone (NMP) was used as the slurry solvent, and polyvinylidene fluoride (PVDF) was used as the binder. Lithium cobaltate (LiCoO ₂ ) having an average particle size of 3 μm was used for the positive electrode substrate,
A slurry composed of artificial graphite powder as a conductive agent, PVDF as a binder, and NMP as a solvent was applied. The obtained electrode in a dry state was further molded by a roll press, and cut into predetermined dimensions to obtain an electrode. The positive electrode was housed in a bag-shaped separator, and a microporous film of a polyethylene material having a thickness of 25 μm was bent in a U-shape to wrap the positive electrode, and both sides of the U-shape were thermally welded. FIG. 1 shows a bag-shaped separator according to the present invention.
2 shows a positive electrode inserted into the data. In the figure, 1 is a positive electrode, 3 is a bag-shaped separator, and 4 is a welded portion thereof. Since the lower end of the figure is a folded portion, there is no welded portion. In this example, the welding conditions at this time were examined, and heating was performed until the mating surfaces for welding were mutually fused. As a result, the welded portion of the white separator became transparent, and at this time, the transmittance of visible light in the wavelength range of 500 to 700 μm became 10% or more. A prismatic battery was manufactured by combining the positive electrode and the negative electrode inserted in the bag-like separator thus welded. The electrode dimensions were 55 mm × 67 mm, comprising 18 positive electrodes and 19 negative electrodes, and the battery capacity was 3.0 Ah. The electrode group was housed in a rectangular metal container, an electrolyte was injected, and the container was closed to form a sealed battery. Twenty of the batteries thus obtained were naturally dropped from a height of 1.5 m onto a concrete floor 10 times, and then charged and discharged at a current of 1 CmA between 4.2 V and 2.8 V. Was repeated 10 times, and then dropped naturally onto a concrete floor from a height of 1.5 m 10 times, and then charged and discharged 10 times with a current of 1 CmA between 4.2 V and 2.8 V. . As a result, the first 1
In zero charge / discharge, the discharge capacity is 2.97 Ah on average,
The average discharge capacity is 2.96 A even after 10 charge / discharge cycles.
h, and no significant capacity reduction was observed.

Comparative Example A battery was manufactured in the same manner as in the example. However, the bag separator was welded under the condition that the white separator did not become transparent. All other conditions are the same as in the embodiment. AA batteries were manufactured in the same manner as in the above example except for the specifications and manufacturing method of the other electrodes. Twenty of the obtained batteries were subjected to a drop-charge-discharge-drop-charge-discharge test under the same conditions as in the above example. As a result, the average discharge capacity was 2.97 Ah in the first 10 charge / discharge cycles, and the average discharge capacity was 2.73 A in the subsequent 2.97 Ah charge / discharge cycles.
h, and a slight decrease in capacity was observed. In addition, two of the twenty batteries tested underwent internal short circuits and exhibited unstable open circuit voltages.

[0008]

According to the present invention, in a prismatic secondary battery having a structure in which at least one of the positive electrode and the negative electrode is housed in a bag made of a polyolefin-based material, the bag-like separator is welded. By welding under the condition that the processed portion becomes transparent, a robust battery structure that does not easily cause a short circuit even when repeated rapid charging and discharging or impact is enabled.

[Brief description of the drawings]

FIG. 1 is a view showing a bag-like separator into which a positive electrode according to the present invention is inserted and a welded portion thereof.

FIG. 2 is a diagram showing an electrode group configuration of a prismatic battery using the electrode according to the present invention.

[Explanation of symbols]

 1. 1. positive electrode Negative electrode 3. Bag-shaped separator 4. Welded part of bag-shaped separator

Claims (6)

[Claims] 1. A positive electrode having a positive electrode active material mixture layer formed on an electrode substrate, a negative electrode having a negative electrode active material mixture layer formed on an electrode substrate, and a separator interposed between the two electrodes. And a battery in which a battery component made of an electrolytic solution distributed over the three components is housed in a square airtight container, wherein at least one of the positive electrode and the negative electrode is welded with a polyolefin-based material. A prismatic secondary battery having a structure accommodated in a bag-shaped separator, wherein a welded portion of the bag-shaped separator is transparent. 2. The prismatic secondary battery according to claim 1, wherein an unwelded portion is present in the welded portion of the bag-shaped separator. 3. The prismatic secondary battery according to claim 1, wherein the polyolefin-based material constituting the bag-like separator is polyethylene, polypropylene or a coexisting material thereof. 4. The prismatic secondary battery according to claim 1, wherein the prismatic secondary battery is applied to a lithium ion secondary battery. 5. A positive electrode having a positive electrode active material mixture layer formed on an electrode substrate, a negative electrode having a negative electrode active material mixture layer formed on an electrode substrate, and a separator interposed between the two electrodes. And a method for producing a prismatic secondary battery in which battery components made of an electrolytic solution distributed over the three components are housed in a prismatic closed container, wherein at least one of the positive electrode and the negative electrode is formed by welding a polyolefin-based material. A part to be welded to form a bag-shaped separator by heating or compression or a combination of heating and compression to form a transparent welded portion, which is housed in a processed bag-shaped separator. Is a method of manufacturing a prismatic secondary battery. 6. The method of manufacturing a prismatic secondary battery according to claim 5, wherein an unwelded portion is present in the welded portion of the bag-shaped separator.