JP2003109575A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a battery of which, a current collecting lead drawn out from an electrode is welded at least to an outer case or to a sealing body, so as not to generate defective conduction caused by a breakage of a welded part of the current collecting lead even when a shock caused by fall-down or a vibration is added. SOLUTION: Peripheral part of a sealing plate 31 and an opening end part of an outer case 10 are sealed by laser welding, and the top end part of a positive electrode lead 222 is also welded to this welded sealing part, and a slit 224 is formed to the positive electrode lead 222 so as to include the neighboring area of the welded part 222A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a case where an electrode body is housed in an outer can, an opening of the outer can is closed by a sealing body, and a current collecting lead pulled out from the electrode body is used for the outer can and the sealing body. More specifically, the present invention relates to a battery welded to at least one side, and particularly to a welded sealed battery in which an outer can and a sealing body are sealed by welding.

[0002]

2. Description of the Related Art In recent years, as the demand for mobile devices such as mobile phones, AV devices, and computers has increased, the demand for sealed secondary batteries, especially for lithium secondary batteries, has increased. This sealed secondary battery is a positive electrode plate and a negative electrode plate wound via a separator to produce an electrode body,
Produced by accommodating the electrode body in an outer can formed by forming a metal plate into a bottomed tubular shape, attaching a sealing plate to the opening of the outer can, and sealing the opening of the outer can and the outer periphery of the sealing plate. Has been done.

The shape of the sealed secondary battery is generally cylindrical or prismatic. In particular, the prismatic sealed battery has been attracting attention because it is excellent in space efficiency when it is mounted on a portable device, and expectations are particularly high for a thin prismatic sealed battery. Sealing is performed to prevent leakage of electrolyte and gas, and is often performed by mechanical caulking, but when sealing by caulking is difficult, especially in the case of prismatic sealed batteries, etc. In many cases, sealing by laser welding is performed.

Regarding current collection from the electrode body, for example, in a lithium secondary battery having an aluminum alloy as an outer can, a sealing plate is generally welded to the outer can to serve as a positive electrode terminal together with the outer can, and a negative electrode terminal. Is attached on the sealing plate in an insulating state from the sealing plate. The positive electrode plate and the outer can are electrically connected via a positive electrode current collector, and the negative electrode plate and the negative electrode terminal are electrically connected via a negative electrode current collector.

Here, as the current collector, a thin metal plate (for example, a nickel plate or an aluminum plate having a thickness of 0.1 mm) is usually used, and the current collector and the electrode plate are joined to each other. The connection with the terminal is made by welding.
By the way, Japanese Unexamined Patent Publication No. 9-171809 discloses a technique in which a current collecting lead is drawn out from a positive electrode core and the drawn current collecting lead is also welded at the same time when welding the outer can and the sealing body. If the technology is used, welding between the positive electrode current collector and the positive electrode plate is not necessary, and separate welding between the positive electrode current collector and the positive electrode terminal is not necessary. Therefore, the number of welding times can be reduced accordingly and the manufacturing process can be reduced. It can be simplified.

By the way, in general, in a portable device,
Since there is a possibility of dropping or vibration during use, the sealed battery is also required to have a capability of stably supplying electric power even when a shock or vibration is applied to the battery.

[0007]

However, when a sealed battery is manufactured by welding the current collecting lead at the same time when the outer can and the sealing body are welded as described above, a drop impact or vibration is applied to the battery. Sometimes the current collecting lead is easily broken along the welded part. Then, if the current collecting lead is broken, conduction failure occurs. That is, the internal resistance becomes extremely high and becomes unstable, so that electric power cannot be stably supplied.

The reason why the welded portion is easily broken is that a thin metal foil is usually used as the core material, but the current collecting leads are also formed of the same metal foil, so that Considering that it is difficult to obtain the tensile strength of the current collecting lead and that the welding point between the current collecting lead and the outer can is the same position as the welding point between the outer can and the sealing body, it is easy to apply a pulling force to the current collecting lead. To be

[0009] Here, if the width of the welding portion of the current collecting lead is set to be large, it may be less likely to break, but in reality, the width of the welding portion of the current collecting lead is also limited by the size of the outer can. Therefore, it cannot be set too large. The present invention is a battery in which a current collecting lead drawn out from an electrode body is welded to at least one of an outer can and a sealing body, even if a drop impact or vibration is applied to the battery, the welded portion of the current collecting lead is broken. The purpose is to prevent the occurrence of defective conduction.

[0010]

In order to achieve the above object, the present invention provides a battery in which a current collecting lead drawn from an electrode body is welded to at least one of an outer can and a sealing body. Is divided into a plurality of lead pieces at least in the region near the welded portion.

Alternatively, one or more slits may be formed in the collector lead so as to cover the vicinity of the welded portion. When a current collection lead is broken by falling impact or vibration, generally, a crack occurs along the welding line at the widthwise end of the lead, and this crack grows along the welding line. Although a large amount of force is consumed when a crack first occurs, which leads to rupture, once the crack occurs, the crack extends even if a small force is applied.

Here, as described above, if the current collecting lead is divided into a plurality of lead pieces in the region near the welded portion, or in the current collecting lead, the current collecting lead is applied to the position near the welded portion. In addition, if one or more slits are formed, a lot of force is consumed for cracking in each lead piece before all of the lead pieces are broken, so that drop impact or vibration is applied to the battery. However, the breakage of the lead is less likely to occur.

The number of slits formed in the current collecting lead is preferably 5 or less.

[0014]

FIG. 1 is a perspective view of a prismatic sealed battery according to an embodiment of the present invention. FIG. 2 is a partial cross-sectional view of the sealing lid in this prismatic sealed battery. This prismatic sealed battery is a lithium secondary battery, in which an electrode body in which a nonaqueous electrolytic solution is impregnated in a spirally wound electrode body 20 is housed inside a bottomed prismatic outer casing 10. This is a structure in which the opening of the above is sealed with a sealing lid 30.

The outer can 10 is formed by forming a plate of an Al--Mn alloy into a square cylinder with a bottom. The spiral electrode body 20 is
The negative electrode plate 21 and the positive electrode plate 22 (see FIG. 3B) are wound in an elliptical cross section through a separator. 3A is a front view and a bottom view of the positive electrode plate 22 before winding, and FIG. 3B is a front view and a bottom view of the negative electrode plate 21 before winding.

The negative electrode plate 21 is formed by coating layered carbon (graphite powder) on a plate-shaped core body (for example, a copper foil having a thickness of 18 μm). A negative electrode lead 212 is attached to the negative electrode plate 21, and is electrically connected to the negative electrode terminal 32 via the negative electrode lead 212. on the other hand,
In the positive electrode plate 22, a positive electrode mixture composed of a lithium-containing oxide (for example, lithium cobalt oxide) as a positive electrode active material and a conductive agent (for example, acetylene black) is a plate-shaped core body (for example, an aluminum foil having a thickness of 20 μm). And is electrically connected to the outer can 10 also serving as a positive electrode terminal via the positive electrode lead 222.

In the outermost peripheral portion of the spirally wound electrode body, the positive electrode core body is exposed and the positive electrode core body and the inner surface of the battery outer can contact each other. Further, the positive electrode lead 222 is formed by providing a substantially U-shaped notch (a shape corresponding to the notch 223) in the outermost peripheral portion of the positive electrode core 220 and inverting the notch. Are fixed to the outer peripheral surface of the spiral electrode body 20 with a protective tape 25.

The non-aqueous electrolyte solution with which the electrode body 20 is impregnated is prepared by mixing LiPF ₆ as a solute at a concentration of 1 mol / l in a mixed solvent having a volume mixing ratio of ethylene carbonate and diethyl carbonate of 40:60. It is melted. The sealing lid 30 is configured such that the negative electrode terminal 32 is attached near the center of the sealing plate 31.

In the sealing lid 30, a negative electrode terminal 32 and the like are attached to a sealing plate 31 formed in a rectangular shape so that a plate made of the same aluminum alloy as the material of the external can 10 fits into the opening of the external can 10. The sealing plate 3
The outer peripheral portion 1 and the opening edge portion 11 of the outer can 10 are sealed by laser welding. The tip portion of the positive electrode lead 222 is also welded and joined to the welded seal portion. In FIG. 1, 222A indicates a welded portion formed in a line on the tip portion of the positive electrode lead 222.

The negative terminal 32 comprises a cap member 320 mounted on a cylindrical sleeve member 321. As shown in FIG. 2, a through hole is formed in the central portion of the sealing plate 31, and the sleeve member 32 is formed in this through hole.
1 is fitted via the gasket 33. An insulating plate 34 made of an insulating resin is attached to the inner surface side of the sealing plate 31. Spacers 34A are integrally formed on both ends of the insulating plate 34, and the spacers 34A are interposed between the electrode body 20 and the sealing plate 31, and serve to prevent contact between the electrode body 20 and the sealing plate 31.

Also, the sleeve member 321 of the negative electrode terminal 32.
A collector plate 35 is connected to the. These insulating plates 3
The negative electrode terminal 3 and the current collector plate 35 are fixed to the sealing plate 31 by caulking and crimping with the sleeve member 321.
2 and the collector plate 35 are in a state of being insulated from the sealing plate 31 by the gasket 33 and the insulating plate 34. The current collector plate 35 is welded to the negative electrode lead 212.

[Characteristics of Positive Electrode Lead 222] Positive Electrode Lead 2
Slits (breaks) 224 are formed in the line 22. This slit 224 has a line-shaped welded portion 222.
It is formed so as to include a position near A. That is, the slit 2
The one end of 24 is formed so as to be located near the welded portion 222A.

The direction in which the slit 224 is formed is
It is preferable that the angle formed by the welding line (the line-shaped welded portion 222A) is a certain size or more (for example, 45 ° or more). In particular, it is preferable to form in a direction substantially perpendicular to the welding line. Further, by forming the slit 224, the vicinity of the welded portion 222A of the positive electrode lead 222 is divided to form a plurality of lead pieces, but the lead pieces should be formed so that their widths are substantially equal. Is preferred.

The number of slits 224 formed in the positive electrode lead 222 may be one or two or more. However, if the number of slits 224 exceeds five, the width of each of the divided lead pieces becomes narrow. Therefore, the number of slits 224 is preferably 5 or less. 4 (A) to (C),
It is a figure which shows the specific example of the form which forms the slit 224 in the positive electrode lead 222, and shows only the welding part 222A vicinity of the positive electrode lead 222 in this figure.

For example, when only one slit 224 is formed as shown in FIG.
In the vicinity of the welded portion 222A of the two lead pieces 22
It is preferably formed perpendicular to the welding line so that it is divided into 5A and 225B. Also, FIG.
As shown in (A) and (B), when two or more slits 224 are formed, the vicinity of the welded portion 222A of the positive electrode lead 222 is a plurality of lead pieces 225A, 225.
It is preferable to form them perpendicularly to the welding line so that they are substantially equally divided into B, ...

[Effects of Characteristics of Positive Electrode Lead 222] FIGS. 5 and 6 are views for explaining a mechanism in which the lead is broken by a drop impact or vibration applied to the lead. FIG. A battery according to the present embodiment in which a slit is formed as shown by 222 is shown, and FIG. 6 shows a battery according to a comparative example in which a slit is not formed in the lead.

First, with reference to FIG. 6, a mechanism in which the lead is generally broken will be described. When a lead is broken by falling impact or vibration, in general, (a) →
As shown in (b), a crack is generated along the welding line at the widthwise end of the lead, and then (b) → (c) →
As shown in (d), the crack grows along the welding line to reach the fracture.

Here, a crack first occurs (a) →
A lot of force is spent in the stage of (b), but once the crack is generated, the crack that has already occurred is triggered and the crack grows. Therefore, in the stage of (b) → (d) The crack grows without spending too much force. That is, in (a) → (d), cracks occur (a) →
The step (b) is the rate-determining step.

On the other hand, as shown in FIG. 5, even when a slit is formed in advance in the lead, the point that the crack grows along the welding line leads to the breakage, but all of the lead pieces are formed. Before breaking, a lot of force is spent to generate a crack even in a place where the slit is formed. That is, not only a large amount of force is consumed for the crack 1 to occur in the steps of (a) → (b), but also one lead piece is ruptured as in (c), and then (c) → ( At the stage of d), a large amount of force is also consumed to generate the crack 2 at the end of the remaining lead piece.

Therefore, when the slit is formed as shown in FIG. 5, the breakage of the lead is less likely to occur than when the slit is not formed as shown in FIG. If the angle between the welding line and the slit is too small, the slit may trigger and cracks may grow along the welding line, but like the slit 224,
If there is a certain angle to the welding line, it will not trigger and the crack will grow.

[0031]

EXAMPLE A method of manufacturing the battery according to the above embodiment will be described. Preparation of positive electrode plate: LiCoO ₂ 85
Parts by weight, 5 parts by weight of artificial graphite powder and 5 parts by weight of carbon black are thoroughly mixed, and then polyvinylidene fluoride (PV
5 parts by weight of dF) is added to dissolved N-methyl-2-pyrrolidone to prepare a positive electrode slurry.

This positive electrode slurry was applied to an aluminum foil (length 335 mm, width 38 mm, thickness 20 μm) to be the positive electrode core 220.
m) and then dried to form the positive electrode active material layer 221. This is rolled by a roller press machine, 110 ℃
The positive electrode plate 22 is manufactured by vacuum drying for 3 hours. In addition, from the winding end portion of the positive electrode core to 20 mm,
The positive electrode active material layer is not applied to both surfaces of the positive electrode core, and the core is exposed, and the positive electrode active material layer is applied to only one surface of the positive electrode core in the range of 20 to 50 mm from the end of winding.

The notch 223 in the exposed portion of the core body
Make a notch in a U-shape at the location where you want to form. In this embodiment, the tip of the positive electrode lead 222 (the welded portion 2
22A) has a width of 5 mm. Preparation of Negative Electrode Plate: Particle size 5 to 25 μm as a negative electrode mixture
N-methyl-2-pyrrolidone in which 5 parts by weight of PVdF is dissolved is added to 95 parts by weight of the above-mentioned natural graphite powder to prepare a negative electrode slurry.

A copper foil (length 315 mm, width 39 mm, thickness 18 μm) to be the negative electrode core 210 was prepared from this negative electrode slurry.
Both surfaces are coated on the above and dried to form a negative electrode active material layer 211. By rolling this with a roller press and spot welding a nickel plate as the negative electrode lead 212 to the end portion, vacuum drying treatment is performed at 110 ° C. for 3 hours.
The negative electrode plate 21 is produced.

Preparation of spiral electrode body: The negative electrode plate 21 is covered with a strip separator made of polyethylene, and the strip positive electrode plate 2 is formed.
2 and are laminated and wound. At the time of this winding, the portion in which the positive electrode active material layer is applied to only one surface of the positive electrode core is wound so as to face the inside of the spirally wound electrode body. As a result, the positive electrode core body is exposed at the outermost peripheral portion of the spirally wound electrode body 20.
The winding end portion is fixed with a winding end tape (not shown) and flatly crushed to produce the spiral electrode body 20.

Assembly of Battery: The sealing lid 30 is placed on the upper part of the spiral electrode body 20 and the negative electrode lead 212 and the current collector plate 35 are welded and electrically connected. Spiral electrode body 20
In, the positive electrode lead 222 is formed (the cutout 223 is also formed) by reversing the substantially U-shaped cut portion of the exposed portion of the positive electrode core body. Then, the positive electrode lead 222 is fixed to the outer peripheral surface of the spirally wound electrode body 20 with the protective tape 25. At this time, the tip of the positive electrode lead 222 is adjusted to slightly exceed the upper surface of the sealing plate.

Next, the spiral electrode body 20 is inserted into the outer can 10 and the sealing lid 30 is fitted into the opening of the outer can 10. At this time, the exposed portion of the positive electrode core body located at the outermost periphery of the spirally-wound electrode body contacts the inner surface of the outer can. The positive electrode lead 222 is sandwiched between the outer can opening edge and the sealing plate 31. The tip of the positive electrode lead 222 is the sealing plate 31.
If it protrudes much more than the upper surface of the, adjust by cutting it to an appropriate length.

Finally, the outer can 10 and the sealing plate 31 are welded by irradiating them with laser light along the boundary between them. At the time of this welding, the tip portion (welded portion 222A) of the positive electrode lead 222 is also welded and electrically connected to the outer can 10 and the sealing plate 31 at the same time. After laser welding, a non-aqueous electrolyte solution is injected from the hole of the sleeve member 321 into the inside of the outer can 10 using a nozzle for injecting the electrolyte solution, and the cap member 320 is fixed to the crimped upper end of the sleeve member 321. By doing so, a battery is manufactured.

Since the thickness of the positive electrode lead 222 is as thin as 20 μm, the spirally wound electrode body can be easily inserted into the battery outer can and, even when sandwiched between the battery outer can and the sealing plate, a large gap is generated on the fitting surface. Never. Therefore, the positive electrode current collector can be reliably welded to the battery outer can and the sealing plate by laser welding. Formation of Slits: In this embodiment, the welded portion 222A is formed at the end of the positive electrode lead 222.
The slit 224 is formed by making a cut with a cutter so as to be perpendicular to the line.

The number and position of slits are shown in FIG.
In the example of (A), one slit is formed in the center of the positive electrode lead 222 in the width direction. In the example of FIG. 4B, three slits are provided and the width of each of the three lead pieces is 1.5 mm. In the example of FIG. 4C, five slits are formed and the width of each of the five lead pieces is 0.7 mm. Regarding the length of the slit, in any case, the line of the welded portion 222A is used. It is formed up to 2.5 mm away from the center.

Regarding the timing of forming the slit 224 in the positive electrode lead 222, it may be formed when the substantially U-shaped cut is formed in the positive electrode plate manufacturing process,
It may be formed after reversing the positive electrode lead 222 in the battery assembling process. [Experiment] As shown in FIGS. 4 (A) to 4 (C), five batteries according to the example in which one, three, and five slits were formed in the positive electrode lead 222 were prepared, and at the same time, the positive electrode lead 222 was formed. Five batteries of Comparative Example were prepared in the same manner except that the slit was not formed.

Then, a drop test was conducted on each of the batteries of the examples and comparative examples (five cells each) as follows. First, the internal resistance (IR) of the battery is measured before the drop test. Next, the battery is dropped onto the concrete plane from a height of 30 cm. At this time, the battery is dropped six times in total with the six surfaces of the battery facing downward to form one set.

Then, every time one set of drops is performed,
The internal resistance (IR) of the battery is measured, and the test is terminated when the measured internal resistance fluctuates by ± 10% or more with respect to the internal resistance before the drop test. Here, based on the judgment that when the internal resistance of the battery fluctuates by ± 10% or more, it means that all of the lead pieces are broken, the number of sets until the end is monitored as the number of broken sets.

FIG. 7 shows the test results, and shows the number of sets for each battery until the end of the test. In the figure, the mark ○ indicates the average of the number of sets until the end of the test for each battery. Shows. Further, Table 1 shows the average value (AVE.), The maximum value (MAX.), And the minimum value (MIN.) Of the number of sets up to the end of the test for each battery.

[0045]

[Table 1] From the results of FIG. 7 and Table 1, it is understood that the number of break sets in the battery of the example is larger than that of the battery of the comparative example, that is, the leads are less likely to be broken by a drop impact.

In the battery of the embodiment, the slit 1 is used.
It can be seen that the number of break sets of the book is larger than that of the slit of 3 or 5. It is considered that this is because the larger the number of slits, the smaller the width of each lead piece affects the easiness of breakage. From this, it is considered that the number of slits to be formed should be 5 or less.

(Modifications, etc.) Regarding the form of the slit formed in the positive electrode lead, in addition to the linear cut as described in the above embodiment, a curved cut may be made, or an elongated shape. You may make a cutout (for example, wedge-shaped). Further, in the above embodiment, the positive electrode lead was formed by cutting a part of the positive electrode core, but in the case of forming a positive electrode lead by connecting a metal foil different from the positive electrode core to the positive electrode core. Also, if a slit is formed in the positive electrode lead in the same manner, the same effect can be obtained.

Further, in the above embodiment, an example in which the sealing plate and the outer can are sealed by laser welding has been shown, but the same can be applied to those welded by electron beam or the like. it can. Further, in the above-described embodiment, the battery in which the positive electrode lead drawn from the positive electrode core is welded to the welded portion between the outer can and the sealing body is shown. The same can be applied to a battery in which the negative electrode lead drawn from the core is welded.

Further, the battery is not limited to the battery in which the outer can and the sealing body are sealed by welding, but the lead drawn from the electrode plate is welded to the outer can or the sealing body, and the outer can and the sealing body are sealed by caulking or the like. It can also be applied to stopped batteries. Further, in the above-described embodiment, the prismatic sealed lithium secondary battery has been described as an example. However, the invention can be similarly applied to a cylindrical sealed battery, and batteries other than the lithium secondary battery (alkaline secondary battery) Etc.)

[0050]

As described above, according to the present invention,
In a battery in which a current collecting lead drawn from an electrode body is welded to at least one of an outer can and a sealing body, by dividing the current collecting lead into a plurality of lead pieces at least in a region near the welded portion, or In the current collecting lead, by forming one or more slits so as to reach the position near the welded portion in the current collecting lead, even if the battery is subjected to a drop impact or vibration, the lead is less likely to break.

Therefore, the present invention is an effective technique especially for manufacturing a battery for portable equipment.

[Brief description of drawings]

FIG. 1 is a perspective view of a prismatic sealed battery according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a sealing lid in the prismatic sealed battery.

FIG. 3 is a diagram showing a negative electrode plate and a positive electrode plate before winding.

FIG. 4 is a diagram showing a specific example of a form in which a slit is formed in a positive electrode lead.

FIG. 5 is a diagram illustrating a mechanism in which the lead of the battery according to the embodiment is broken when a drop impact or vibration is applied to the lead.

FIG. 6 is a diagram illustrating a mechanism in which a lead of a battery according to a comparative example is broken when a drop impact or vibration is applied to the lead.

FIG. 7 is a diagram showing the results of a drop test.

[Explanation of symbols]

10 exterior cans 11 Opening edge 20 spiral electrode body 21 Negative electrode plate 22 Positive plate 31 sealing plate 32 negative terminal 35 current collector 220 Positive electrode core 222 Positive electrode lead 222A welded part 224 slit 225 lead piece

Claims (3)

[Claims] 1. An electrode body, in which a positive electrode plate and a negative electrode plate are opposed to each other with a separator interposed therebetween, is housed in an outer can, and the opening of the outer can is closed by a sealing body and pulled out from the electrode body. A current collecting lead is a battery welded to at least one of the outer can and the sealing body, and the current collecting lead is divided into a plurality of lead pieces at least in a region in the vicinity of the welded portion. Characteristic battery. 2. An electrode body in which a positive electrode plate and a negative electrode plate are opposed to each other with a separator interposed therebetween is housed in an outer can, and the opening of the outer can is closed by a sealing body and pulled out from the electrode body. In the battery, the current collecting lead is welded to at least one of the outer can and the sealing body, and one or more slits are formed in the current collecting lead so as to extend to a position near the welded portion. A battery characterized by being 3. The battery according to claim 2, wherein the number of slits formed in the current collecting lead is 5 or less.