JPH1167188A - Lead terminal for secondary battery and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain an electric discharge resistance low, while providing a fuse element. SOLUTION: A lead piece of a current collection body side 12 is connected to an electrode current collection body, and the leas piece for electric discharge 13 is branched from here and also the lead piece for electric charge circuit 12 is provided via a fuse element 14. The fuse element 14 and one part of respective lead pieces 11-13 are sandwiched by resin films 15 and stored in a battery case.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery lead terminal provided with a fuse and a lithium secondary battery incorporating the same.

[0002]

2. Description of the Related Art For example, a lithium secondary battery is provided with a resistance element (PCT) having a positive temperature characteristic or a thermal fuse at an external electrode portion of a battery case in order to suppress heat generation during overcharge, and is charged when the temperature rises. The current is cut off.

[0003]

However, in the above configuration, there is a problem that the protection elements such as the PCT and the thermal fuse are bulky and the whole battery cannot be reduced in size. Also,
In the above configuration, safety is effectively ensured during overcharging, but during discharging, only the internal resistance of the battery is increased, which is rather obstructive.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lithium secondary battery capable of eliminating a problem at the time of discharging while securing safety at the time of overcharging. And a lead terminal for a secondary battery.

[0005]

According to a first aspect of the present invention, there is provided a secondary battery lead terminal for connecting an electrode current collector of a secondary battery to an external circuit via a fuse. A current collector side lead piece connected to the electrode current collector side, a charging circuit lead piece connected to the charging circuit of the secondary battery, and a connection between the current collector side lead piece and the charging circuit lead piece. Element, a resin film sandwiching the fuse element together with a part of each of the lead pieces from both sides of the front and back of the fuse element and closely adhering to each other. And a discharge circuit lead piece connected to the discharge circuit of the secondary battery.

In a lithium secondary battery according to a second aspect of the present invention, an electrode body formed by winding an electrode sheet having an electrode current collector is accommodated in a battery case, and the lead terminal according to the first aspect of the present invention. Are disposed in the battery case and connected to the electrode body, and a part of the lead pieces for the charging circuit and the lead pieces for the discharging circuit is led out of the battery case as external terminals.

According to a third aspect of the present invention, there is provided a lithium secondary battery according to the second aspect, wherein the battery case is formed in a bag shape sealed by a resin film, and the resin film of the lead terminal for the secondary battery is provided. The feature is that the portion is sandwiched between the sealing portions of the battery case.

A lithium secondary battery according to a fourth aspect of the present invention has an electrode body housed in a battery case and has external terminals connected to the respective electrode current collectors on the positive and negative electrode sides of the electrode body. Wherein the external terminal includes a charging external terminal connected to one electrode current collector via a fuse element, and a discharging external terminal connected to the one electrode current collector without a fuse element. It is characterized by comprising a terminal and a common external terminal connected to the other electrode current collector.

[0009]

According to the lead terminal for a secondary battery of the present invention, since the fuse element and the lead piece are sandwiched between the resin films, the sheet becomes small and bulky as a whole. Therefore, the size and weight of the secondary battery can be reduced. Moreover, since it is thin and sealed with a resin film, it has a high degree of freedom in arrangement, and can be arranged near a heat source to improve responsiveness. Further, since the charging circuit lead is connected to the charging circuit of the secondary battery, a charging current flows through the fuse element during charging. Therefore, when the temperature inside the secondary battery rises abnormally due to overcharging, the fuse element is blown and the charging current is interrupted to ensure safety. Further, since the discharge circuit lead piece is connected to the discharge circuit of the secondary battery, the discharge current does not pass through the fuse element, and no unnecessary increase in the internal resistance occurs.

According to the lithium secondary battery of the present invention, a part of the charging lead piece serves as a charging external terminal, and a part of the discharging lead piece serves as a discharging external terminal. Therefore, by connecting an external charging circuit to the external charging terminal and connecting an external discharging circuit to the external discharging terminal, it is possible to detect an abnormal temperature rise during charging and cut off the charging current, while the fuse element is discharged. Thus, an effect of preventing an increase in internal resistance due to the above can be obtained. Of course, since the lead terminals have a small sheet shape while having the fuse function as described above, the size and weight of the secondary battery can be reduced.

According to the lithium secondary battery of the third aspect, since the battery case is made of a resin film, the battery case can be further reduced in size and weight, and the resin film portion of the lead terminal for the secondary battery is formed by the sealing portion of the battery case. Because it is sandwiched between
The sealing property of the battery case is improved.

According to the lithium secondary battery of the present invention, the charging circuit is connected to the external charging terminal and the common terminal during charging, and the discharging circuit is connected to the external discharging terminal and the common terminal during discharging. Therefore, if an abnormal temperature rise occurs during charging,
The fuse element is blown and the charging current is cut off to ensure safety. Further, at the time of discharging, a discharge current can be flowed without passing through the fuse element, and an increase in internal resistance can be avoided.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2
Shows a lead terminal 10 for a negative electrode according to the present invention. In the figure,
Reference numeral 11 denotes a charging circuit lead piece, which is formed in a narrow strip shape, for example, by a nickel foil. Reference numeral 12 is a current collector side lead piece also formed of nickel foil, from which a discharge circuit lead piece 13 branches off and is integrally formed. The discharge circuit lead pieces 13 are provided in parallel with the charge circuit lead pieces 11 at a predetermined interval.

A thin strip-shaped fuse element 14 made of a low melting point alloy is connected between the charging circuit lead 11 and the current collector side lead 12 by spot welding. They are connected in a straight line.

The lead pieces 11 to 13 and the fuse element 14 are sandwiched between two resin films 15 from both the front and back sides, and both films 15 are heat-pressed. As a result, the lead terminal 10 is formed in a sheet shape as a whole, and as shown in FIG. 2, the two films 15 are in close contact with each other and sealed at a portion where the lead pieces 11 to 13 and the fuse element 14 are left. ing. The resin film 15 is made of a modified polyolefin (“EVAL” (registered trademark) manufactured by Kuraray Co., Ltd.). However, various materials can be used as long as they have resistance to an electrolytic solution constituting a battery and necessary insulation and heat resistance.

The structure of a lithium secondary battery using the above-described negative electrode lead terminal 10 will be described with reference to FIGS.
This will be described with reference to FIG. This battery has a belt-like positive electrode sheet 1
6 and the negative electrode sheet 17 are wound together with the separator 18 in a flat cloth shape to form a bag-shaped battery case 20.
It is configured to be housed in a storage device. The positive electrode sheet 16 is formed by applying a positive electrode mixture 22 (shown with oblique cross lines in the figure) such as lithium cobalt oxide (LiCoO2) on both surfaces of an aluminum foil 21 as an electrode current collector. A negative electrode mixture 24 such as graphite (shown with diagonal lines crossed down in the figure) is applied to both surfaces of a copper foil 23 as an electrode current collector.

The positive electrode mixture layer 21 is not applied to the end of the aluminum foil 21 of the positive electrode sheet 16, and a positive electrode lead terminal 25 made of aluminum is connected thereto by ultrasonic welding. Are projected above the electrode body 19. A region where the negative electrode mixture 24 is not applied is also formed at the end of the copper foil 23 of the negative electrode sheet 17, and the current collector-side lead piece 12 of the positive electrode lead 10 is also connected by ultrasonic welding. Both ends of the charging circuit lead 11 and the discharging circuit lead 13 protrude above the electrode body 19. A resin film 26 of the same material as the resin film 15 of the negative electrode lead terminal 10 is fixed to the intermediate portion of the positive electrode lead terminal 25 in the same manner as the negative electrode lead terminal 10.

As shown in FIGS. 6 and 7, the positive electrode sheet 16 and the negative electrode sheet 17 are stacked with a separator 18 interposed therebetween except for left and right ends, and as shown in FIG. It is wound so as to be folded repeatedly, and becomes a flat cloth. In this wound state, the positive electrode mixture layer 21 and the negative electrode mixture layer 23 are opposed to each other with the separator 18 interposed therebetween, and the nonaqueous electrolyte solution impregnated in the separator 18 (for example, ethylene carbonate, diethyl carbonate, and dimethyl carbonate are mixed together). 1: 2 mixed liquid to which lithium hexafluorophosphate is added) to form a lithium secondary battery.

The electrode body 19 is accommodated in the battery case 20 through an opening thereof, and the battery case 20 is sealed by closing the opening and press-bonding the same while the electrolyte is being injected therein. As shown in FIG. 8, the resin film 15 of the lead terminal 10 for the negative electrode and the resin film 26 of the lead terminal 25 for the positive electrode are sandwiched in the sealing portion, and the opening edges of the resin films 15 and 26 and the battery case 20 are sandwiched. And are tightly adhered. With the battery case 20 sealed in this way, as shown in FIG.
25 has an upper end protruding from the battery case 20, and the upper end of the positive electrode lead terminal 25 has a common external terminal 25.
A, and the upper end of the charging circuit lead piece 11 of the negative electrode lead terminal 10 becomes a charging external terminal 11A,
The upper end of the discharge circuit lead piece 13 is the external terminal 13 for discharge.
A. The battery case 20 is made of, for example, PET27, aluminum foil 2 as shown in FIG.
8. A laminated film in which an adhesive layer 29, a first modified polyolefin layer 30 and a second modified polyolefin layer 31 are sequentially laminated, and the second modified polyolefin layer 31 is folded inside with the bottom side and side portions welded. Thereby, it is formed in a bag shape in advance, and finally the upper opening is sealed.

In the lithium secondary battery having the above configuration, the common external terminal 25A and the charging external terminal 11A are connected to an external charging circuit, and the common external terminal 25A and the discharging external terminal 1A are connected.
3A is connected to an external discharge circuit. If the battery generates heat due to overcharging during charging, the temperature of the fuse element 14 built in the negative electrode lead terminal 10 in the battery case 20 rises almost without delay. When the temperature rises to, for example, 130 ° C., the fuse element 14 is melted, the conduction between the charging circuit lead piece 11 and the current collector side lead piece 12 is cut off, the charging current is cut off, and safety is ensured. You. The upper and lower sides of the fuse element 14 are sandwiched between the resin films 15. However, the adhesiveness between the fuse element 14 and the resin film 15 is not always good, and the thickness between the upper and lower resin films 15 depends on the thickness of the fuse element 14. Because there is a slight gap in
The melt in which the fuse element 14 is melted is rounded by the surface tension in the gap or the like, so that conduction between the lead pieces 11 is interrupted. Since the resin film 15 of the negative electrode lead terminal 10 is made of a modified polyolefin, the resin film 15 tends to shrink by heat. However, since the discharge circuit lead piece 13 is sandwiched beside the fuse element 14, the resin film 15 at that portion has Shrinkage of the resin film 15 is suppressed, and circuit interruption due to melting of the fuse element 14 is reliably performed.

In discharging, the discharge current flows from the current collector side lead piece 12 to the discharge circuit lead piece 13 without passing through the fuse element 14. Therefore, the fuse element 1
4, the useless internal resistance is not generated, and the battery performance is improved.

Further, the lithium secondary battery using the negative electrode lead terminal 10 is housed in the battery case 20 because the negative electrode lead terminal 10 itself is in a sheet shape and thin while incorporating the fuse element 14 therein. Even so, the whole battery will not be bulky. In addition, since it is arranged at a position closest to the electrolyte solution and the positive electrode mixture 22 which generate heat at the time of overcharging and is directly affected by heat, responsiveness is enhanced and safety is excellent.

When the negative electrode lead terminal 10 is built in the battery case 20 and the circuit on the negative electrode side is cut off as described above, the following difficulties can be expected. In other words, if the battery case is made of metal and has the same potential as the negative electrode side as in a conventional general battery, it is assumed that the temperature fuse is operated to move the negative electrode sheet of the electrode body from the charge / discharge circuit. Even when separated, the inner surface of the battery case is still maintained at the negative electrode potential. Then, lithium ions in the electrolytic solution precipitate here as metallic lithium, which grows and comes into contact with the positive electrode side, which may cause a short circuit accident. To avoid such a dangerous situation, it is necessary to connect the battery case, which has the same potential as the negative electrode side, to the charge / discharge circuit via a thermal fuse.To do so, install a thermal fuse outside the battery case. I have to. Then, since the thermal fuse is moved away from the heat source, the responsiveness of the thermal fuse is lowered, which is not preferable.

On the other hand, in the present embodiment, the battery case 20 is formed of a laminated resin film having the second modified polyolefin layer 31 inside, and its inner surface is insulated from the electrolytic solution. For this reason, the negative electrode lead terminal 1 having the built-in fuse element 14 to improve the responsiveness
0 is disposed in the battery case 20 to disconnect the negative electrode side of the electrode body 19 from the charging / discharging circuit.
Dangerous situations such as precipitation of metallic lithium during the operation of 4 can be reliably prevented.

[Second Embodiment]

FIGS. 11 and 12 show a second embodiment of the present invention. The difference from the first embodiment is that the fuse element 1
The current collector side lead piece 12 of the negative electrode lead terminal 10 containing the lead 4 is formed to be long so as to protrude downward from the copper foil 23 of the negative electrode sheet 17 to form a discharge circuit lead piece 13. In this configuration, as shown in FIG. 12, the lower end of the discharge circuit lead piece 13 protrudes from the lower part of the battery case 20, and serves as a charging external terminal 13A. Other configurations are the same as those of the first embodiment, and the same portions are denoted by the same reference numerals, and duplicate description will be omitted. In this configuration, the same effects as those of the first embodiment can be obtained.

[Other Embodiments] The present invention is not limited to the embodiment described above with reference to the drawings and drawings. For example, the following embodiments are also included in the technical scope of the present invention. In addition to the following, various changes can be made without departing from the scope of the invention. (1) In the above embodiment, an example was shown in which the negative electrode lead terminal 10 according to the present invention was applied to a lithium secondary battery. However, the present invention is not limited to this and can be widely applied to other types of secondary batteries. . (2) In the above embodiment, the electrode body 19 and the battery case 2
Although 0 has a flat shape, it is needless to say that these may be formed in a cylindrical shape. (3) In the above embodiment, the lead terminal according to the present invention is provided on the negative electrode side, but may be provided on the positive electrode side. In addition, simply connecting a charging external terminal to one of the positive electrode side and the negative electrode side of the lithium secondary battery via a fuse element, and connecting a fuse element to the other part of the electrode current collector. Directly connect the discharge external terminal without passing through,
A configuration in which a common external terminal is connected to the other electrode current collector may be adopted.

[Brief description of the drawings]

FIG. 1 is a perspective view of a lead terminal according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the same lead terminal.

FIG. 3 is a perspective view of the electrode body and the battery case.

FIG. 4 is a plan view of the same positive electrode sheet.

FIG. 5 is a plan view of the same negative electrode sheet.

FIG. 6 is an exploded perspective view of the same electrode body.

FIG. 7 is an exploded perspective view showing a winding process of the electrode body.

FIG. 8 is a perspective view showing a lithium secondary battery in a completed form.

9 is a cross-sectional view taken along the line IX-IX of FIG.

FIG. 10 is an enlarged sectional view of the same laminated film.

FIG. 11 is a plan view of a negative electrode sheet according to a second embodiment of the present invention.

FIG. 12 is a perspective view showing a lithium secondary battery in the same completed form.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Lead terminal 11 ... Charge piece lead piece 12 ... Current collector side lead piece 13 ... Negative discharge circuit lead piece 14 ... Fuse element 15 ... Resin film 16 ... Positive electrode sheet 17 ... Negative sheet 19 ... Electrode body 20 ... Battery case 21 ... Aluminum foil (electrode current collector) 23 ... Copper foil (electrode current collector) 26 ... Resin film 11A ... Charge external terminal 13A ... Discharge external terminal 25A ... Common external terminal

Claims (4)

[Claims] 1. A lead terminal for connecting an electrode current collector of a secondary battery to an external circuit via a fuse, wherein the current collector side lead piece connected to the electrode current collector side; A charging circuit lead piece connected to the battery charging circuit;
A fuse element provided so as to connect between the current collector side lead piece and the charging circuit lead piece, and a resin which sandwiches the fuse element together with a part of each of the lead pieces from both front and back sides of the fuse element and adheres to each other; A lead terminal for a secondary battery, comprising: a film; and a lead piece for a discharge circuit, which is provided integrally with the lead piece on the electrode current collector side and connected to a discharge circuit of the secondary battery. 2. An electrode body formed by winding an electrode sheet provided with an electrode current collector is housed in a battery case, and the lead terminal according to claim 1 is arranged in the battery case to form the electrode. A lithium secondary battery connected to a body, wherein a part of the lead pieces for the charging circuit and the lead pieces for the discharging circuit are led out of the battery case as external terminals. 3. The battery case according to claim 1, wherein the battery case is formed in a bag shape sealed with a resin film, and the resin film portion of the lead terminal for the secondary battery is sandwiched in a sealing portion of the battery case. 2. The lithium secondary battery according to 2. 4. An electrode body is housed in a battery case,
In the one having an external terminal connected to each of the positive electrode side and the negative electrode side electrode current collector of the electrode body, the external terminal is a charging external terminal connected to one of the electrode current collectors via a fuse element. A lithium secondary battery comprising: a discharge external terminal connected to the one electrode current collector without a fuse element therebetween; and a common external terminal connected to the other electrode current collector.