JP2004319463A

JP2004319463A - Secondary battery

Info

Publication number: JP2004319463A
Application number: JP2004095091A
Authority: JP
Inventors: Hideaki Fujita; Yasutaka Furuyui; Tatsuya Hashimoto; Tetsuya Niimoto; 康隆古結; 哲也新本; 達也橋本; 秀明藤田
Original assignee: Matsushita Electric Ind Co Ltd; 松下電器産業株式会社
Priority date: 2003-03-28
Filing date: 2004-03-29
Publication date: 2004-11-11

Abstract

PROBLEM TO BE SOLVED: To provide a highly safe secondary battery capable of preventing the occurrence of a thermal runaway reaction due to overcharge in advance.
SOLUTION: An outer case 2 accommodating a power generation element therein and serving as one electrode terminal, the other electrode terminal 3 arranged on the outer case 2 via an insulating member, and expansion due to an increase in internal pressure of the outer case 2 A short-circuit mechanism such as a current-carrying member 4 and a connecting member 5 for short-circuiting the outer case 2 and the other electrode terminal 3 by deformation is provided. The internal pressure rises almost proportionally according to the degree of overcharging, and the outer case 2 expands accordingly. When a predetermined pressure is reached, the short-circuit mechanism is activated, and the outer case 2 and the other electrode terminal 3 are short-circuited. As a result, a short-circuit current flows and battery energy is dissipated before a thermal runaway reaction of the battery occurs.
[Selection diagram] Fig. 1

Description

The present invention relates to a secondary battery, and more particularly to a secondary battery provided with an overcharge safety mechanism.

When the secondary battery is overcharged, the internal pressure rises, an exothermic reaction occurs, the battery temperature rises, and depending on the use conditions, the gas in which the active material is thermally decomposed due to the temperature rise , Which may cause a thermal runaway reaction of the battery.

Conventionally, as a safety mechanism against such dangerous behavior at the time of overcharging, by melting the current-carrying member between the power generation element and the electrode terminal in the outer case due to temperature rise, to cut off the current path, There is known a device in which a connection component connecting a power generation element and an electrode terminal is destroyed by an increase in internal pressure to cut off a current path and stop further charging.

A secondary battery having a configuration as shown in FIG. 6 is also known. In FIG. 6, reference numeral 11 denotes a group of electrodes as a power generating element configured by stacking a positive electrode plate and a negative electrode plate with a separator interposed therebetween, and is inserted and disposed in an outer case 12. A current collector (not shown) to which one electrode plate at one end of the electrode plate group 11 is connected is connected to the bottom surface of the outer case 12, and a collector to which the other electrode plate at the other end of the electrode plate group 11 is bonded. The electric body 13 is connected to a sealing member 15 that seals the opening of the outer case 12 via an insulating gasket 14. A concave portion 16 for positioning the sealing member 15 is formed in the opening of the outer case 12. Reference numeral 17 denotes a safety valve provided on the sealing member 15. The current collector 13 is provided with a spring member 18 that constantly presses the gasket 14 outward in the radial direction (for example, see Patent Document 1).

In this secondary battery, when the temperature rises to a predetermined temperature or higher due to overcharging, as shown in FIG. 7A, the gasket 14 is melted by heating, and the tip of the spring member 18 comes into contact with the outer case 12 and is short-circuited. When the internal pressure rises to a predetermined pressure or higher, the concave portion 16 expands and deforms as shown in FIG. 7B, and the tip of the spring member 18 comes into contact with the outer case 12 to be short-circuited, and the battery energy is discharged. It is consumed and the overcharge state is prevented from continuing.
JP-A-10-106532

By the way, at the time of overcharging, the current path between the power generating element and the electrode terminal is cut off by heating and melting the current-carrying member, or as shown in FIG. The characteristic of the accompanying temperature rise is that the temperature rise is gradual in the middle of the process and suddenly increases just before the thermal runaway reaction of the battery occurs. There is a problem that it is not enough.

Also, in the method in which the current path between the power generating element and the electrode terminal is interrupted by the pressure destruction of the connection part during overcharge, the connection part must be made of thin parts in order to surely break it with the rise in pressure. As a result, there is a problem that the energization resistance is increased and the output is reduced. Further, as shown in FIG. 7B, in the method in which the recess 16 of the outer case 12 is plastically deformed by pressure and short-circuited, if the strength and rigidity of the outer case 12 are ensured, short-circuit will not occur unless an extremely large pressure is generated. Therefore, there is a possibility that the operating point of the safety mechanism may be delayed, and there is a problem that the reliability of the safety mechanism is not sufficient.

The present invention has been made in view of the above-described conventional problems, and has as its object to provide a highly safe secondary battery that can prevent the occurrence of a thermal runaway reaction due to overcharge in advance.

The secondary battery according to the first aspect of the present invention includes an outer case that houses a power generating element therein and serves as one electrode terminal, the other electrode terminal disposed on the outer case via an insulating member, and an internal pressure of the outer case. It is provided with a short-circuit mechanism for short-circuiting the outer case and the other electrode terminal by expansion and deformation caused by the rise.

According to the above configuration, by utilizing the fact that the internal pressure rises almost proportionally according to the degree of overcharge and the external case expands accordingly, when the internal pressure becomes a predetermined internal pressure by the short-circuit mechanism, the external case and the other Since the electrode terminals are short-circuited and a short-circuit current flows, the battery energy is dissipated before the thermal runaway reaction of the battery occurs, and the thermal runaway reaction can be reliably prevented from occurring.

Further, a current-carrying member, which is provided with a short-circuit mechanism, is disposed opposite to a portion that expands due to an increase in the internal pressure of the external case, and is disposed with an interval so as to be in contact with each other when the internal pressure of the external case becomes equal to or higher than a predetermined pressure. When it is configured with a connection member for connecting the other electrode terminal, the inner pressure of the outer case and the displacement amount of the expanded portion correspond accurately, so that when the inner pressure of the outer case reaches a predetermined pressure, the outer case and the conductive member Can be reliably short-circuited by contact with each other, and a highly reliable safety mechanism can be realized.

Further, the short-circuit mechanism may be configured by a current-carrying member that is fixed to a portion that expands and deforms with an increase in the internal pressure of the outer case, and that contacts the other electrode terminal when the inner pressure of the outer case becomes equal to or higher than a predetermined pressure.

In addition, by providing a resistor for limiting the current value to the connection member or the conducting member, it is possible to suppress a short-circuit current and to control the amount of heat generated by the short-circuit current.

In the first aspect of the invention, it is effective to pay attention to the deformation of the side surface of the outer case as the expansion deformation due to the increase of the internal pressure of the outer case, and it is particularly effective to pay attention to the deformation of the side surface of the substantially rectangular parallelepiped outer case having the widest area. is there. On the other hand, the above-mentioned first invention relates to the case where the outer case itself serves as one electrode terminal, but it is not always necessary to achieve the same object as the first invention. For example, the top end surface of the outer case In the case of a secondary battery with a positive electrode terminal and a negative electrode terminal protruding in parallel with each other, a thermal runaway reaction of the battery occurs due to short-circuiting between the two electrode terminals due to expansion deformation due to an increase in internal pressure on the side surface of the outer case during overcharge. It is also possible to configure so as to prevent the problem beforehand, and the following second invention generally shows such a configuration.

That is, the second invention of the present application includes a first contact portion electrically connected to one of the positive electrode terminal and the negative electrode terminal, and a second contact portion electrically connected to the other electrode terminal. When the internal pressure of the outer case becomes equal to or higher than a predetermined pressure, the first contact portion moves and comes into contact with the second contact portion along with the expansion deformation due to the increase of the inner pressure on the side surface of the outer case, and one electrode terminal and the other electrode terminal are connected. It is configured to be short-circuited.

Also in the second invention, similarly to the first invention, a resistor for limiting a current value is provided on a short-circuit path connecting one electrode terminal and the other electrode terminal so as to suppress heat generation due to the short-circuit current. It is preferable to set to.

Further, in the second invention, a fuse which is blown by the short-circuit current is provided in a common path between a short-circuit path connecting one electrode terminal and the other electrode terminal and a charging path for supplying a charging current to the secondary battery. It is preferable to provide them. With this configuration, the fuse can be blown by flowing a large current of 10 times or more in the case of a short circuit as compared with a normal charging current, thereby stopping the progress of overcharging and providing a safer safety mechanism. realizable. In addition, there is a problem that the resistor is large in size and the cost is high. However, this problem can be solved by using a fuse.

According to the secondary battery of the present invention, the internal pressure rises almost proportionally according to the degree of overcharging, and the outer case is deformed accordingly, so that when the internal pressure reaches a predetermined internal pressure, the outer case and the other end are short-circuited. Is short-circuited, a short-circuit current flows, and the battery energy is dissipated before the thermal runaway reaction of the battery occurs. Therefore, the occurrence of a thermal runaway reaction can be prevented from occurring.

Hereinafter, a first embodiment of the secondary battery of the present invention will be described with reference to FIGS. The basic internal configuration of the secondary battery is the same as that described with reference to FIG. 6, and the description is omitted here and the description is omitted here.

In FIG. 1, reference numeral 1 denotes a secondary battery such as a lithium ion battery or the like, and reference numeral 2 denotes an outer case of the secondary battery. For example, in the case of a lithium ion battery, the electrode plate group includes a positive electrode plate formed by applying a positive electrode mixture containing a positive electrode active material such as LiCoO _{2 to} a current collector core material such as an aluminum foil, and a lithium ion battery. A negative electrode plate composed by applying a negative electrode mixture containing a negative electrode active material such as a carbon material to be absorbed and desorbed to a current collector core material such as copper foil, and a separator composed of a microporous polyethylene film are laminated. It is configured.

The outer case 2 is connected to one polarity electrode plate of the electrode plate group to form one electrode terminal (a negative electrode terminal in the case of a lithium ion battery). Reference numeral 3 denotes an electrode terminal of the other polarity (a positive electrode terminal in the case of a lithium ion battery) disposed on the outer case 2 via an insulating member, and is connected to the other electrode plate of the electrode group.

Note that the outer case 2 of the present embodiment is formed in a rectangular parallelepiped shape, and an electrode plate group in which a large number of rectangular positive and negative electrode plates are stacked with a separator interposed therebetween, or a strip-shaped positive and negative electrode plate is formed by forming a separator. A group of electrode plates, which are stacked via a wire and wound around a flat core, are stacked. Of course, a cylindrical outer case similar to the conventional example shown in FIG. 6 may be used, but in the case of the rectangular outer case 2, the side surface, in particular, the flattened almost rectangular outer case 2 has the largest area. Since the expansion deformation of the side surface is large, the effect of applying the present invention is large.

A current-carrying member 4 made of a metal plate or a metal-plated synthetic resin plate is disposed facing the side surface of the outer case 2 of the secondary battery 1 at an appropriate distance d, and the current-carrying member 4 and the electrode terminals 3 are provided. Are connected by the connection member 5. When the internal pressure of the outer case 2 becomes equal to or higher than a predetermined pressure due to overcharging of the secondary battery 1, the distance d between the outer case 2 and the conducting member 4 is equal to the maximum expansion point ( The first contact portion) 54 and the corresponding point (second contact portion) 55 of the conducting member 4 are set so as to contact each other. The connecting member 5 and the current-carrying member 4 are integrally formed with each other, and are fixed to the electrode terminal 3 formed by the positive electrode cover to form a holding member 56 that holds the second contact portion 55. However, it is also possible to fix the holding member 56 and a case accommodating the secondary battery 1, for example, and connect the second contact portion 55 held by the holding member 56 and the electrode terminal 3 by wiring.

As shown in FIG. 1 (c), the connection member 5 is provided with a resistance member in the middle as necessary, or a material having an appropriate resistance value is used as a material of the connection member 5. A resistor 6 is provided, and is configured to control short-circuit current to control heat generation due to the short-circuit current. In FIG. 1C, reference numeral 51 denotes a charging power source, and 52 denotes a charging path.
In the secondary battery having the above configuration, at the time of charging, the SOC (State of Charge: here, SOC means the percentage of the amount of electricity input to the nominal capacity of the battery) exceeds 100% during charging. In this state, as shown in FIG. 2, as the SOC increases, the internal pressure of the outer case 2 gradually increases almost proportionally, and when a runaway reaction occurs, for example, immediately before the SOC becomes about 200%, abruptly occurs. And then the safety valve is activated to release the pressure.

On the other hand, the battery temperature rises very slowly even when the SOC exceeds 100%, starts to rise at a stage before the thermal runaway reaction occurs, and sharply rises immediately before. Therefore, there is a problem that the safety mechanism based on the temperature rise may not operate beforehand as described in the conventional example.

In the present embodiment, as described above, the phenomenon that the outer case 2 expands and deforms in response to the pressure increase that gradually increases in accordance with the degree of overcharge is used, and increases with the progress of overcharge. When the pressure reaches a predetermined pressure, the outer case 2 comes into contact with the conductive member 4 due to the expansion and deformation of the outer case 2 as shown in FIG. 2 and the electrode terminal 3 are short-circuited. In particular, since the inner pressure of the outer case 2 and the displacement amount of the expanded portion correspond accurately, the outer case 2 and the current-carrying member 4 come into contact with each other when the inner pressure of the outer case 2 reaches a predetermined pressure. I do. Thus, the occurrence of a situation in which a short-circuit current flows to dissipate battery energy and cause a thermal runaway reaction is prevented, and a highly reliable safety mechanism is realized. The overcharge state detection operation range is between 20% and 80% between the overcharge start point (SOC 100% and the thermal runaway reaction point (SOC 200% in the example of FIG. 2)), and optimally 20-40%. If it is set between%, an ideal safety function can be achieved.

In addition, if a resistor 6 for limiting the current value is provided in the connection member 5 or the conducting member 4, in other words, in the short-circuit path 53, the short-circuit current can be suppressed, so that the amount of heat generated by the short-circuit current can be controlled. It is.

Next, a second embodiment of the battery of the present invention will be described with reference to FIG. In the above-described embodiment, an example is described in which the short-circuit occurs due to the displacement of the antinode portion of the side surface when the outer case 2 is inflated and deformed. As described above, the base of the current-carrying member (tilting member) 7 is fixed to one end of the side surface of the outer case 2 where the electrode terminal 3 is provided, and the electrode terminal (second contact portion) is attached to the current-carrying member 7. An abutting portion (first contact portion) 8 is provided so as to protrude so as to be close to 3 with an appropriate gap. When the internal pressure of the outer case 2 becomes equal to or higher than a predetermined pressure due to overcharging of the secondary battery 1, the gap between the arrangement position of the contact portion 8 and the electrode terminal 3, as shown in FIG. The current-carrying member 7 is inclined so that the contact member 8 comes into contact with the electrode terminal 3 as the member 2 expands and deforms. In FIG. 3, the charging power source and the charging path are omitted, but are the same as those in FIG.

Also in the present embodiment, as in the first embodiment, when the internal pressure of the outer case 2 reaches a predetermined pressure, the contact portion 8 of the conducting member 7 fixed to the outer case 2 and the electrode terminal 3 come into contact with each other. As a result, a short circuit is reliably caused, a short circuit current flows, battery energy is dissipated, and the occurrence of a thermal runaway reaction is prevented, thereby realizing a highly reliable safety mechanism.

In addition, by providing a resistor for controlling the current value in the conducting member 7 or the contact portion 8 thereof, the short-circuit current can be limited, and the amount of heat generated by the short-circuit current can be suppressed, which is preferable.

Next, a third embodiment of the present invention will be described with reference to FIGS. The secondary battery of the present embodiment is a battery for a power source mounted on an automobile and is a relatively large lithium-ion battery, and its outer case 2 has a flat and substantially rectangular parallelepiped shape. The outer case 2 has an oval cross section, a height a of 100 mm, a width b of 60 mm, and a thickness c of 10 mm.

The basic configuration of the present embodiment is the same as that of the first embodiment, and the outer case 2 itself constitutes one electrode terminal, and the outer case 2 has a distance d (approximately 5 mm) on the side surface 2a having the largest area. The current-carrying member 4 is disposed with a gap. The other electrode terminal 3 of the secondary battery 1 and the current-carrying member 4 are integrally connected via a connecting member 5. The current-carrying member 4 is disposed in parallel with the side surface 2a, and a fuse 61 that is blown at the time of a short circuit is provided at an intermediate portion of the connection member 5.

The maximum expansion point of the side surface 2a is the first contact portion 54 of the one electrode terminal (exterior case) 2, and the portion of the conducting member 4 facing the first contact portion 54 is the second contact portion 55. . One end of the charging power source 51 is connected to the outer case (one electrode terminal) 2, and the other end is connected to a position of the connection member 5 that is closer to the conducting member 4. The fuse 61 is arranged in the charging path 52 to which the charging current of the charging power supply 51 is supplied. However, the fuse 61 is not blown during normal charging.

When the internal pressure of the outer case 2 becomes equal to or higher than a predetermined pressure due to overcharging of the secondary battery 1, as shown by a virtual line in FIG. The short-circuit current (for example, about 2000 A) flows through the short-circuit path 53 and blows the fuse 61 disposed on a common path with the charging path 52 when the second contact section 55 of the current-carrying member 4 is contacted. Thereafter, when the charging current is not supplied to the secondary battery 1, the progress of overcharging can be stopped, and a highly reliable safety mechanism can be realized.

Note that the fuse 61 of this embodiment can be applied to the second embodiment and the like.

Further, as shown in the present embodiment, it is preferable to apply the present invention to a secondary battery having a relatively large, flat, substantially rectangular parallelepiped outer case 2, wherein the height a is 50 mm or more, and the lateral width b is It is suitable to apply to a secondary battery having the outer case 2 of 30 mm or more.

1 shows a first embodiment of a secondary battery of the present invention, (a) is a schematic configuration diagram in a normal state, (b) is a schematic configuration diagram of an operation state of a safety mechanism at the time of overcharge, and (c) is a schematic circuit. FIG. 6 is a graph showing the relationship between the amount of overcharge of the secondary battery and the pressure and temperature. 3A and 3B show a second embodiment of the secondary battery of the present invention, in which FIG. 4A is a schematic configuration diagram of a normal state, and FIG. 4B is a schematic configuration diagram of an operation state of a safety mechanism during overcharge. It is a schematic structure perspective view showing a 3rd embodiment of a rechargeable battery of the present invention. It is a schematic structure figure showing the operation state of the above-mentioned embodiment. It is a longitudinal cross-sectional view of the conventional secondary battery. FIG. 7A is a vertical cross-sectional view showing a state in which a gasket is melted, and FIG. 7B is a vertical cross-sectional view showing a case where a concave portion of an outer case is plastically deformed.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Secondary battery 2 Outer case 3 Electrode terminal 4 Current supply member 5 Connection member 6 Resistance 7 Current supply member

Claims

An outer case that houses the power generating element therein and serves as one electrode terminal, the other electrode terminal disposed on the outer case via an insulating member, and the outer case and the other electrode by expansion deformation due to an increase in the internal pressure of the outer case. A secondary battery comprising a short-circuit mechanism for short-circuiting terminals.
The short-circuit mechanism is provided with a current-carrying member disposed opposite to a portion which is expanded due to an increase in the internal pressure of the outer case and spaced apart from each other when the internal pressure of the outer case becomes a predetermined pressure or more, and The secondary battery according to claim 1, comprising a connection member for connecting the electrode terminal.
2. The secondary circuit according to claim 1, wherein the short-circuit mechanism is constituted by a current-carrying member that is fixed to a portion that expands and deforms with an increase in the internal pressure of the outer case, and that contacts the other electrode terminal when the internal pressure of the outer case exceeds a predetermined pressure. battery.
4. The secondary battery according to claim 2, wherein a resistance for limiting a current value is provided on the connecting member or the conducting member.
A first contact portion electrically connected to one of the positive electrode terminal and the negative electrode terminal; and a second contact portion electrically connected to the other electrode terminal, wherein an inner pressure of the outer case is equal to or higher than a predetermined pressure. The first contact portion moves along with the expansion and deformation due to the increase of the internal pressure on the side surface of the outer case and comes into contact with the second contact portion to short-circuit one electrode terminal and the other electrode terminal. Features a secondary battery.
A first contact portion is provided on a side surface of the outer case, and a second contact portion is arranged outside the outer case. When the second contact portion faces the first contact portion and the internal pressure of the outer case becomes equal to or higher than a predetermined pressure. The secondary battery according to claim 5, further comprising a holding member that holds the first contact portion at an interval so as to contact the first contact portion.
7. The secondary battery according to claim 6, wherein the outer case itself is one electrode terminal, and the first contact portion is formed by a side surface of the outer case.
A first contact portion is provided at a tip end of a tilting member having a base fixed to a side surface of the outer case, and a second contact portion is disposed outside the outer case so as to face the first contact portion at an interval. 6. The secondary according to claim 5, wherein when the internal pressure of the case becomes equal to or higher than a predetermined pressure, the tilting member tilts with the expansion due to the increase of the internal pressure on the side surface of the outer case, and the first contact portion contacts the second contact portion. battery.
9. The outer case itself is one electrode terminal, the tilting member is made of a conductive member, the first contact portion is formed of the tilting member itself, and the second contact portion is formed of the other electrode terminal itself. Rechargeable battery.
The secondary battery according to any one of claims 5 to 9, wherein a resistor for limiting a current value is provided in a short-circuit path connecting one electrode terminal and the other electrode terminal.
A fuse which is blown by the short-circuit current is provided in a common path between a short-circuit path connecting one electrode terminal and the other electrode terminal and a charging path for supplying a charging current to the secondary battery. 10. The secondary battery according to any one of 9 above.
The secondary battery according to claim 1, wherein the outer case has a substantially rectangular parallelepiped shape.
6. The outer case has a substantially rectangular parallelepiped shape and is flat, and the first contact portion moves and comes into contact with the second contact portion in accordance with expansion and deformation caused by an increase in internal pressure on the side surface having the largest area. 12. The secondary battery according to any one of claims 11 to 11.
14. The secondary battery according to claim 12, wherein the outer case has a substantially rectangular cross section.
14. The secondary battery according to claim 12, wherein the outer case has an oval cross section.