JP2001325943A - Flat cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat cell of new structure with an over current protecting function. SOLUTION: For the flat cell of which, one end part of a metal foil 3a of a resistor element 3 with positive temperature coefficient, is connected to one terminal 2a of a pair of foiled terminals 2a, 2b extended from a terrace-shaped periphery sealing part 1a. The resistor element 3, composed of a pair of metal foil 3a, 3b, interposing a conductive polymer with positive thermal coefficient in between, is housed in a space 1A of the peripheral sealing part interposing a thermal insulation material 4 arranged on the periphery sealing part 1a, and the shape of horizontal projection of the resistor element 3 is L-shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat battery, and more particularly, to a flat battery having a novel structure having an overcurrent protection function.

[0002]

2. Description of the Related Art In recent years, as various electronic devices such as mobile phones and portable personal computers have been reduced in size and weight, their driving power sources have been required to have a battery characteristic such as high energy density. In addition to improvements, demands for further downsizing and weight reduction are increasing. In particular, the demand for thinning is remarkable.

In order to meet such a demand, for example, Li
In the case of an ion secondary battery, research on a flat battery using a polymer solid electrolyte film as an electrolyte is underway. This flat battery usually has, for example, Li on one side of, for example, an Al foil on which a tongue-shaped positive electrode terminal is integrally formed.
A positive electrode formed by applying a mixture containing CoO ₂ as a main component, and a mixture containing, for example, a carbon material is applied to one surface of, for example, a Ni foil on which a tongue-shaped negative electrode terminal is integrally formed. Between the anode and the negative electrode, a polymer solid electrolyte film is arranged to form a power generating element, and an exterior material such as an Al laminated film having outer dimensions larger than the positive electrode and the negative electrode is disposed so as to cover both surfaces of the power generating element. The power generation element is sealed by heat-sealing the peripheral portion of each package material, and the thickness thereof is usually about 3 to 4 mm.

Here, one example of the shape of a flat battery is shown in FIG. In the flat battery 1, the above-described power generation element (not shown) is wrapped from one end of the flat battery 1 by one elongated exterior material, and a side edge of the exterior material located on the upper side and a side edge of the exterior material located on the lower side are provided. Are thermally fused to form a side edge sealing portion, and the portions of the exterior material located on the other end side of the power generating element are also thermally fused to each other to form a sealing portion. The peripheral sealing portion 1 located on one side in the longitudinal direction of the entire battery
a, a tongue-shaped positive electrode terminal 2a made of, for example, Al
And a negative electrode terminal 2b made of, for example, Ni and also having a tongue shape.

[0005] As described above, in the flat battery 1, three peripheral sealing portions are formed by heat-sealing of the exterior material, and thereafter, of these peripheral sealing portions, a side portion of the entire battery is formed. The located peripheral sealing portion is referred to as a side peripheral sealing portion, and the peripheral sealing portion 1a on the positive / negative terminal side is referred to as a terminal-side peripheral sealing portion. In the case of this flat battery 1, two side peripheral edge sealing portions 1b, 1b
Is bent upward. Therefore, in the terminal side peripheral sealing portion 1a, a terrace-shaped space portion 1A is formed which is surrounded by the screen-like both sides formed by the bent side peripheral sealing portion and the side of the power generating element. ing.

[0006] Incidentally, flat batteries have low strength characteristics due to their small thickness, and the exterior material is a material which is easily damaged by external damage such as an Al laminate film. It is housed in a housing and used for actual use. At the same time, the protection circuit board on which the predetermined protection circuit components are mounted is accommodated in a state where the protection circuit board is connected to both terminals of the flat battery by, for example, spot welding.

In such a case, the protection circuit component is generally designed to exhibit the following functions. One is an overcharge protection function for controlling the charging current to prevent the overcharge state from occurring and to ensure the safety of the battery. Also,
This is an over-discharge protection function that prevents pole reversal, internal pressure rise, and performance degradation due to over-discharge. Further, an overcurrent protection function for protecting the battery from an overcurrent generated when the battery is externally short-circuited is provided.

Incidentally, with the recent improvement in the performance of flat batteries, there is no longer any concern about safety even in an overcharged state, and the overcharge protection function for flat batteries can be reduced. Also, depending on the magnitude of the leakage current of the battery body, if this leakage current is small, it is possible to eliminate the overdischarge protection function. As described above, the overdischarge protection function and the overdischarge protection function for the flat battery can be deleted, but since an external short circuit can occur regardless of the battery performance, the protection function against overcurrent based on this external short circuit is still necessary. is there.

Conventionally, such protection against overcurrent has been
It is customary to use a current fuse.

[0010]

However, when a current fuse is used as a measure against overcurrent, there are the following problems. For example, if an overcurrent occurs due to an external short circuit, the current fuse is blown by the resistance heating, so that the battery is certainly protected from the overcurrent. However,
Once blown, the current fuse does not perform its original function, and when the current fuse blows, the flat battery has already lost its overcurrent protection function.

An object of the present invention is to solve the above-mentioned problem in a conventional flat battery provided with an overcurrent protection function by a current fuse, and to provide a flat battery having a new structure in which the overcurrent protection function is restored again when cooled. I do.

[0012]

Means for Solving the Problems In the course of intensive studies in order to achieve the above-mentioned object, the present inventor conceived of using a resistor element having a positive temperature coefficient instead of a current fuse as described later. In that case, various studies were repeated in consideration of not increasing the thickness of the flat battery and not complicating the wiring involved in connection with the terminal, and the like, leading to the development of the flat battery of the present invention. .

That is, in the flat battery of the present invention, one end of a pair of foil-like terminals drawn out from a terrace-shaped peripheral sealing portion is connected to one end of a resistor element having a positive temperature coefficient. Wherein the resistor element is accommodated in the peripheral sealing portion via a heat insulating material disposed on the peripheral sealing portion. .

The resistor element used has a conductive polymer sheet having a positive temperature coefficient interposed between a pair of metal foils, and has an L-shape in plan view. Is preferred.

[0015]

FIG. 1 shows an example of a flat battery according to the present invention. FIG. 1 is a partial perspective view showing a state where a resistor element 3 described later is accommodated in a terrace-shaped space 1A of the flat battery 1 shown in FIG. First, the resistor element 3 will be described.

As shown in FIG. 2, the resistor element 3 has a conductive polymer sheet 3c having a positive temperature coefficient interposed between two metal foils 3a and 3b made of, for example, Ni. It is structured and usually has a thickness of 0.5
It is about 1.5 mm. In the conductive polymer sheet 3c, for example, carbon particles, which are conductors, are dispersed in a polymer, which is an insulator. In a normal state, that is, at normal temperature, the conductive paths formed by the carbon particles reduce the resistance. Has become.

However, as the temperature increases from room temperature, the thermal expansion of the polymer, which is an insulator, progresses, and the above-described conductive path is cut, so that the electric resistance value gradually increases. That is, the positive temperature coefficient (positive
temperature coefficient (PTC). Then, when the temperature reaches a certain temperature, the resistance value sharply rises and is substantially converted into an insulator.

Then, as the temperature decreases, the behavior reverse to that described above is exhibited, and in the normal state, the state is restored to the original low resistance state again. The flat battery according to the present invention includes the above-described PTC.
It is assembled using a resistor element 3 having characteristics. In this case, as shown in FIG. 2 and FIG. 3, a resistor element 3 in which metal foils 3a and 3b are arranged orthogonal to each other and whose shape in plan is L-shaped is used. Is preferred.

At the time of assembling, first, as shown by the arrow in the figure, a pair of terminals pulled out from the terminal side peripheral sealing portion 1a of the flat battery, specifically, the positive electrode terminal 2a of Al
The end of one of the metal foils 3a of the resistor element 3 is brought into contact with the lower surface of the resistor element 3 to connect them. Specifically, the positive electrode terminal and the metal foil are overlapped, and the two are connected by ultrasonic welding.

Next, the positive electrode terminal 2a is bent toward the terrace-shaped space 1A. At this time, the heat insulating material 4 is provided in the terrace-shaped space 1A. Due to the bending of the positive electrode terminal 2a, as shown in FIG. 1, the resistor element 3 is arranged on the heat insulating material 4 in a state of being turned upside down, and is accommodated in the terrace-shaped space 1A. And the resistor element 3
The other metal foil 3b is parallel to the negative electrode terminal 2b,
A extends outward from A.

Here, the heat insulating material 4 is provided to prevent the heat of the resistor element 3 from being transmitted to the enclosed power generating element, although the resistor element is at a high temperature when the resistor element 3 is operated. For example, it is a tape having a base material of polyurethane resin or fiber paper, and has a thickness of about 0.5 to 2 mm. This flat battery has the following effects.

(1) It is assumed that an overcurrent flows through the resistor element 3 due to, for example, an external short circuit. The resistor element 3 starts to exhibit PTC characteristics due to resistance heating and reaches a certain temperature (for example, 100 ° C.).
(° C), it becomes an effective insulator and cuts off the overcurrent to exhibit the overcurrent protection function. When the temperature decreases, the resistance element 3 is restored to a low resistance. That is, due to the PTC characteristics of the low-resistance element, the flat battery has a permanent overcurrent protection function instead of a transient overcurrent protection function.

(2) In the case of this flat battery, the thickness is 0.5
Since the resistor element having a thickness of about 1.5 mm and the heat insulating material 4 having a thickness of about 0.5 to 2 mm are housed in the terrace-shaped space 1A having a height of about 3 to 5 mm, the flat battery The overcurrent protection function is provided without sacrificing the overall thickness. (3) The metal foils 3a and 3b of the resistor element are generally
Because of the i-foil, the output terminals of the flat battery assembled as shown in FIG. 1 are all made of Ni. Therefore, connection with other circuit components and the like can be easily performed.

[0024]

As is apparent from the above description, the flat battery of the present invention has a structure in which a thin resistor element having PTC characteristics is housed in the space of the terminal side peripheral sealing portion. The permanent overcurrent protection function can be exhibited without sacrificing the thinning, and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a partial perspective view showing a main part of a flat battery according to the present invention.

FIG. 2 is a perspective view showing a resistor element having PTC characteristics incorporated in the flat battery of the present invention.

FIG. 3 is a partial perspective view showing a state where the resistor element of FIG. 2 is connected to a flat battery.

FIG. 4 is a perspective view showing an example of a flat battery.

[Explanation of symbols]

 Reference Signs List 1 flat battery 1a peripheral sealing portion (terminal side peripheral sealing portion) 1b peripheral sealing portion (side peripheral sealing portion) 1A space in peripheral sealing portion 1a 2a positive electrode terminal 2b negative electrode terminal 3 positive temperature coefficient Resistor element 3a, 3b Metal foil 3c Conductive polymer sheet 4 Heat insulating material

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Claims (2)

[Claims] 1. A flat battery in which one end of a resistor element having a positive temperature coefficient is connected to one of a pair of foil-like terminals drawn from a terrace-shaped peripheral sealing portion. The flat battery according to claim 1, wherein the resistor element is housed in the peripheral sealing portion via a heat insulating material disposed on the peripheral sealing portion. 2. The resistive element is formed by interposing a conductive polymer sheet having a positive temperature coefficient between a pair of metal foils, and has an L-shape in plan view. Item 10. The flat battery according to Item 1.