JP2002184390A - Cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell with a current breaking device which is enabled to locate at the narrow bottom surface by welding a bimetal 3 to the bottom surface of a cell case 1. SOLUTION: Both end of a bimetal 3 are fixed to the bottom surface of a cell case 1 through insulation materials 2, 3, and the middle part of the bimetal is welded to the bottom surface of the cell case 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery provided with a safety device for interrupting a terminal current when a temperature rises.

[0002]

2. Description of the Related Art A safety device must be provided for a lithium ion secondary battery in order to prevent the battery case from exploding due to a rise in temperature or an increase in internal pressure due to overcharge or the like.
Such safety devices include a current interrupting device that interrupts the current in response to an excessive increase in current, temperature, or internal pressure, and a safety valve that releases the internal pressure when the pressure in the battery case abnormally increases. There is.

[0003]

However, as portable electronic devices have become smaller and lighter in recent years, there is no limit to the demand for thinner lithium ion secondary batteries. There has been a problem that it is difficult to provide a current interrupting device in a battery case of a battery.

[0004] With respect to the safety valve, it is possible to form a structure in which the thickness of a part of the battery case is reduced to break this part when the internal pressure rises and release the high-pressure gas to the thin battery case. is there.

However, in the current interrupting device, a conventional bimetal formed in the form of a diaphragm is connected by being pressed against a contact due to its elasticity, and when the temperature rises abnormally, the bimetal diaphragm is inverted into a flip-flop shape. Because of this, diaphragms with a structure that opens the contacts, or with a structure in which a diaphragm-shaped inversion film is reversed by increasing the internal pressure and the contacts are opened by utilizing the deformation have been used. It is difficult to attach a current interrupting device that is wide due to the shape of the structure to the narrow side surface of the thin battery case. Also, if such a current interrupting device is attached to the widest surface of a thin battery case, it will hinder the battery from being made thin. For this reason, conventionally, it was necessary to provide only a safety valve on a small-sized lithium ion secondary battery itself, and to provide a current interrupting device on an external circuit connected to the lithium ion secondary battery.

The present invention has been made in order to cope with such a situation. By fixing or electrically contacting a bimetal to a battery terminal of a battery case or the like, the present invention can be applied to a narrow surface of the battery case. It is an object of the present invention to provide a battery including a current interrupting device that can be arranged.

[0007]

In the battery according to the present invention, the contact portion is formed by fixing a part of the bimetal to the battery case and fixing the other part to the battery terminal or making electrical contact with the battery terminal. When the temperature rises, the bimetal is deformed so that the bimetal is separated at the contact portion to open the electrical conduction.

According to the first aspect of the present invention, when the temperature rises, the bimetal is deformed, so that the other portion tends to separate from the contact portion with the portion fixed to the battery case as a fulcrum, so that electrical contact is made. If it is, it is separated from the contact portion as it is, and if it is fixed, it is released and the connection with the battery terminal is cut off. For this reason, the current interrupting device can be configured only by fixing a part of the bimetal to the battery case and fixing or contacting the other part. There is no hindrance to thinning.

In the battery according to the present invention, the bimetal has a strip-shaped end portion fixed to the battery case, and a central portion fixed to or electrically connected to the battery terminal to form a contact portion. It is characterized by the following.

According to the second aspect of the present invention, since both ends of the bimetal are fixed to the battery case, the center of the bimetal fixed or contacted to the battery terminal can be reliably supported from both sides, and the current is interrupted. The device can be operated stably.

In the battery according to a third aspect of the present invention, the battery case itself constitutes the positive or negative battery terminal, a part of the bimetal is fixed to the battery case via an insulator, and another one of the bimetals is fixed to the battery case. The contact portion is formed by fixing or electrically contacting the portion with the battery case.

According to the invention of claim 3, since the battery case itself constitutes the battery terminal, it can be connected to the battery terminal only by directly fixing or contacting the bimetal to the battery case. However, since the bimetal needs to be insulated from the battery case except for the connection portion, it is fixed to the battery case via an insulator.

According to a fourth aspect of the present invention, the bimetal is fixed to the battery terminal by spot welding, ultrasonic welding or laser welding, brazing or soldering, or bonding with a conductive adhesive. And

In the case where the bimetal is fixed at the contact portion, it is sufficient that the bimetal is securely connected to the battery terminal at normal times, and is detached from the battery terminal when the temperature is abnormally increased. The invention of claim 4 exemplifies such a fixing method.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 6 show an embodiment of the present invention. FIG. 1 is a partially enlarged perspective view showing a bimetal attached to the bottom surface of a battery can of a lithium ion secondary battery, and FIG. FIG. 3 is a partially enlarged front view showing the bimetal attached to the bottom of the battery can of the lithium ion secondary battery. FIG. 3 shows that the welded portion of the bimetal attached to the bottom of the battery can of the lithium ion secondary battery came off when the temperature rose. FIG. 4 is a partially enlarged front view showing a cantilevered bimetal attached to the bottom of the battery can of the lithium ion secondary battery, and FIG. 5 is a bottom view of the battery can of the lithium ion secondary battery. FIG. 6 is a partially enlarged front view showing a bimetal welded to a protruding protrusion, and FIG. 6 is a partially enlarged front view showing a bimetal directly attached to a bottom surface of a battery can of a lithium ion secondary battery.

In the present embodiment, a lithium ion secondary battery using a thin rectangular battery case will be described. In this lithium ion secondary battery, a power generation element (not shown) is housed in a container-shaped battery can 1, and a lid plate (not shown) is attached to the upper end opening of the battery can 1 by welding. The battery can 1 is made of an aluminum alloy in the shape of a rectangular container. The area of one of the four faces excluding the bottom is much larger than that of the other, and the remaining two
The width of the surface and the bottom surface is extremely thin. The battery can 1 is internally connected to the positive electrode of the power generating element, and the entire battery can 1 constitutes a positive electrode terminal. Also, on the lid plate,
An insulated negative electrode terminal is attached to this cover plate, and is internally connected to the negative electrode of the power generating element. Then, the battery case 1 and the cover plate constitute a battery case of the lithium ion secondary battery. In this specification, the bottom surface of the battery can 1, the two narrower surfaces, and the surface of the lid plate in the lithium ion secondary battery are referred to as side surfaces. These sides are elongated rectangular faces because they are much narrower than the two opposite faces.

As shown in FIGS. 1 and 2, a bimetal 3 is fixed to the bottom surface of the battery can 1 via insulating materials 2 and 2. The bimetal 3 is a conductive metal plate in which two or more metal plates having different coefficients of thermal expansion are stacked in the order of the coefficient of thermal expansion, and is formed in an elongated strip shape. This bimetal 3 has a battery can 1 at both ends via insulating materials 2 and 2.
It is firmly fixed to the bottom surface. Also, at this time, the bimetal 3 is fixed in such a direction that the central portion is curved to the side away from the bottom surface of the battery can 1 as the temperature rises. The insulating materials 2 and 2 are insulators made of a resin, ceramic, or the like for insulating the bottom of the battery can 1 and the bimetal 3. An adhesive or the like is used between the bottom of the battery can 1 and the bimetal 3. Use a material that can be securely fixed by insulation.
In addition, an epoxy-based adhesive or the like may be formed as a layer between the bottom surface of the battery can 1 and the bimetal 3 and used as the insulating material 2.

The center of the bimetal 3 is welded to the bottom of the battery can 1 by ultrasonic welding. At this time, the center of the bimetal 3 may be bent toward the bottom of the battery can 1 by pressing with a horn of ultrasonic welding, or the center may be bent toward the bottom of the battery can 1 at normal temperature. May be used. As a result, bimetal 3
Is connected to the bottom surface of the battery can 1 constituting the positive electrode terminal of the lithium ion secondary battery only through the central welded portion. Then, as shown in FIG. 2, a lead wire 4 is soldered to the bimetal 3 to make connection with an external circuit.

Normally, the lithium ion secondary battery of the above configuration is connected to an external circuit via a bimetal 3 whose central portion is welded to the bottom surface of the battery can 1 serving as a positive electrode terminal. However, when the temperature of the lithium ion secondary battery rises due to overcharging or the like, the central portion of the bimetal 3 tends to bend away from the bottom surface of the battery can 1, and when this temperature rises above a predetermined level, FIG. As shown in (2), the welded portion of the bimetal 3 cannot withstand the deformation stress, and peels off from the bottom surface of the battery can 1 and curves. Therefore, the bimetal 3 cuts off the connection with the bottom surface of the battery can 1, which is the positive terminal, when the temperature rises abnormally, so that it can function as a current cutoff device in the safety device.

The lithium ion secondary battery of the present embodiment is
As described above, a current interrupting device having a simple structure in which both ends of the strip-shaped bimetal 3 are fixed via the insulating materials 2 and 2 and the central portion is welded to the narrow bottom surface of the battery can 1 is provided. Therefore, a safety device other than a safety valve can be provided in the battery itself without hindering the thinning of the lithium ion secondary battery. That is, in the case of a conventional current interrupting device, the bimetal is pressed against the contact with strong elasticity so that a reliable connection can be made.
Since the flip-flop inversion operation had to be performed, the bimetal was formed into a complicated diaphragm-like structure. For this reason, the conventional bimetal cannot be disposed on the bottom surface of the narrow battery can 1 as in the present embodiment because the diaphragm-like structure becomes wide. Further, in the case of the present embodiment, once the welded portion of the bimetal 3 is peeled off due to a rise in temperature, it is not necessarily pressed by the strong elasticity, so that it is easily bent away from the bottom surface of the battery can 1. In addition, there is no need to perform an inversion operation as in a conventional bimetal. Furthermore, since the surface of the battery can 1 made of an aluminum alloy is easily oxidized, a reliable connection cannot be made even when a conventional bimetal is directly pressed, but in this embodiment, the bimetal 3 is welded. Therefore, there is no possibility that the conductivity of the contact portion is deteriorated. In addition, in the conventional lithium ion secondary battery using the battery can 1 made of an aluminum alloy as the positive electrode terminal, the bottom surface of the battery can 1 is easily oxidized, so that a terminal plate made of a clad material such as aluminum and nickel is provided here. The connection with the external circuit is performed by welding, but in the case of the present embodiment, since the bimetal 3 substitutes for the terminal plate, the production cost does not particularly increase.

In the above embodiment, the case where both ends of the bimetal 3 are fixed to the bottom surface of the battery can 1 via the insulating materials 2 and 2 has been described. However, as shown in FIG. May be fixed via the insulating material 2 and the other end may be welded.
In this case, when the temperature is abnormally increased, the welded portion comes off because the other end of the bimetal 3 warps as shown by the one-dot chain line in the figure.

In the above embodiment, the case where the central portion of the bimetal 3 is welded to the bottom surface of the battery can 1 while being bent by the thickness of the insulating materials 2 and 2 has been described, as shown in FIG. A protrusion 1a is formed on the bottom surface of the battery can 1 by the thickness of the insulating members 2 and 2, and the center of the bimetal 3 is welded to the tip of the protrusion 1a. There is no need to deflect 3. In addition, instead of the protruding portion 1a, a positive or negative terminal insulated from the battery can 1 may be provided on the bottom surface and welded here. Also in these cases, when the temperature rises abnormally,
As indicated by the dashed line, the center of the bimetal 3 is the protrusion 1
The welded portion comes off by curving to the side away from a and the like.

In the above embodiment, the case where the bimetal 3 is fixed to the bottom surface of the battery can 1 via the insulating material 2 has been described. However, as shown in FIG. Can be directly fixed to the bottom surface of the battery can 1, and the other portion can be welded to the positive or negative terminal 5 insulated from the battery can 1. In this case, the battery can 1 may be made of an insulating material. However, when the terminal 5 is made of a conductive metal, it is necessary to insulate the terminal 5 from a terminal having a polarity different from that of the terminal 5. Also in these cases, when the temperature rises abnormally, the welded portion comes off because the end of the bimetal 3 warps up as shown by the one-dot chain line in the figure.

In the above embodiment, the case where the bimetal 3 is welded to the bottom surface of the battery can 1 by ultrasonic welding has been described. However, welding may be performed by other welding means such as spot welding or laser welding. Furthermore, the bimetal 3 should normally be securely connected to the bottom surface of the battery can 1, and should come off from the bottom surface due to the deformation stress caused by the difference in expansion coefficient when the temperature rises abnormally. Instead of such welding, it may be fixed by brazing or soldering with a metal braze, or by bonding with a conductive adhesive. Alternatively, instead of these fixings, only electrical contact may be made. Good.

In the above embodiment, the case where the bimetal 3 is attached to the bottom surface of the battery can 1 of the small lithium ion secondary battery has been described. However, the surface to which the bimetal 3 is attached is not necessarily limited to the bottom surface. Other aspects or other aspects may be used. In addition, the present invention is not limited to the lithium ion secondary battery, but can be similarly applied to any battery.

[0027]

As is apparent from the above description, according to the battery of the present invention, a part of the bimetal is fixed to the battery case, and the other part is fixed or brought into contact with the battery terminal. The safety device can be easily attached to the side surface of the battery case, and the safety device can be provided without hindering the thinning of the battery.

[Brief description of the drawings]

FIG. 1, showing one embodiment of the present invention, is a partially enlarged perspective view showing a bimetal attached to a bottom surface of a battery can of a lithium ion secondary battery.

FIG. 2, showing an embodiment of the present invention, is a partially enlarged front view showing a bimetal attached to a bottom surface of a battery can of a lithium ion secondary battery.

FIG. 3 is a partially enlarged front view showing an embodiment of the present invention and showing a state in which a welded portion of a bimetal attached to a bottom surface of a battery can of a lithium ion secondary battery has come off when a temperature rises. is there.

FIG. 4 is a partially enlarged front view showing one embodiment of the present invention and showing a cantilevered bimetal attached to a bottom surface of a battery can of a lithium ion secondary battery.

FIG. 5, showing an embodiment of the present invention, is a partially enlarged front view showing a bimetal welded to a projection projecting from a bottom surface of a battery can of a lithium ion secondary battery.

FIG. 6, showing an embodiment of the present invention, is a partially enlarged front view showing a bimetal directly attached to a bottom surface of a battery can of a lithium ion secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery can 1a Projection 2 Insulation material 3 Bimetal 5 Terminal

Claims (4)

[Claims] 1. A part of a bimetal is fixed to a battery case, and another part is fixed to a battery terminal or electrically contacts to form a contact portion, and the bimetal is deformed when a temperature rises. The battery is separated from the contact portion to open electrical conduction. 2. The battery according to claim 1, wherein both ends of the bimetal are fixed to the battery case, and a contact portion is formed by fixing or electrically contacting a central portion to a battery terminal. The battery according to claim 1. 3. The battery case itself constitutes the positive or negative battery terminal, a part of the bimetal is fixed to the battery case via an insulator, and another part is the battery case. 3. The battery according to claim 1, wherein the contact portion is formed by being fixed to or electrically contacting the battery. 4. The battery according to claim 1, wherein the bimetal is fixed to the battery terminal by spot welding, ultrasonic welding or laser welding, brazing or soldering, or bonding with a conductive adhesive. , 2 or 3.