JPH10154530A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low resistance element which is more inexpensive and can cope even with a large battery by providing a safety mechanism where a member composed of shape memory allay is installed as an element for an electric current breaking mechanism in an Li secondary battery where a composite metallic oxide mainly composed of Li and Co is formed as a positive electrode active material and a carbonaceous material is formed as a negative electrode active material. SOLUTION: An internal terminal 4 is electrically connected by a contact point B to a pressure switch plate 7 having a bursting groove 9, and the pressure switch plate 7 is also electrically continued by a contact point A with an electric current breaking element 30 through a current carrying plate 8 having a pressure releasing hole 5. When the electric current breaking element 30 becomes equal to or higher than a shape memory temperature of a shape memory allay coil 11, the shape memory alloy coil 11 instantly contracts, and the contact point A separates, and an electric current is broken. Therefore, since an electric current is completely and instantly broken differently from a conventional PTC element, a user can quickly cope with an abnormal situation, so that reliability and safety can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery which is inexpensive, has stable discharge characteristics, and has a safety mechanism for instantaneously interrupting current when an abnormality such as a battery temperature rise due to overdischarge or overcharge occurs. It relates to batteries.

[0002]

2. Description of the Related Art In recent years, as personal computers and video cameras have become portable and small-sized communication devices such as portable telephones have become widespread, batteries that serve as power sources for these devices are required to have higher performance and higher reliability. It is becoming. In recent years, in addition to conventionally known Ni-Cd batteries and Ni-hydrogen batteries, which are chargeable / dischargeable secondary batteries, lithium secondary batteries having a higher energy density have been used as such power source batteries. It is becoming mainstream.

[0003] At present, lithium secondary batteries are overcharged due to fire accidents due to overdischarge due to short-circuiting of external terminals due to carelessness of the operator, failure of the charging device during charging or improper rapid charging. To prevent accidents such as voltage, excessive charging current, and reverse connection voltage, the battery internal temperature rises and the battery ruptures, a safety mechanism that limits the current with a PTC element against a rise in battery temperature is used. It is built in. Also, in spite of the operation of the PTC element, if the internal pressure of the battery increases due to decomposition of the electrolytic solution or the like, the rupture groove provided in the metal plate in the battery is broken to release the internal pressure to atmospheric pressure. , To prevent battery explosion and fire.

FIG. 10 shows a basic structure of a safety mechanism of a lithium secondary battery. Here, the lead wire 3 is connected to the internal terminal 4 having the pressure release hole 5,
Is connected to the power generation unit. The internal terminal 4 has a rupture groove 9
The pressure switch plate 7 is electrically connected to the external terminal 15 via the PTC element 21. Further, the internal terminal 4 and the pressure switch plate 7 are separated from each other by an insulator 6 so that conduction is lost when the contact B is peeled off due to an increase in the internal pressure of the battery. It is stored in the battery case 1.

As described above, the rupture groove 9 is provided in the PTC element 2.
Despite the fact that 1 was activated and the current was slightly limited,
When the internal pressure of the battery rises due to decomposition of the electrolytic solution, the contact B is peeled off and the current path is cut off. When the internal pressure of the battery subsequently rises, the rupture groove 9 is broken and the internal pressure is released to the atmospheric pressure. By doing so, it is a safety mechanism that prevents the battery from bursting. Therefore, when the rupture groove 9 is activated, the battery cannot be used. Therefore, a safety mechanism that can eliminate an abnormality occurring in the battery before the rupture groove 9 is activated is very important.

[0006] PTC element 2 as one of the safety mechanisms
Reference numeral 1 denotes a resistor element whose resistance value sharply increases at a certain temperature and suppresses current, and is disposed in a conduction path from the internal terminal 4 to the external terminal 15 in FIG. As a PTC element for a lithium secondary battery, for example, a heating protection element using a conductive polymer such as Polyswitch (registered trademark) polyswitch of Raychem Corporation has a room temperature resistivity of 1%.
Ω · cm, resistance transition temperature 100 ° C, resistance change rate 10
It has the characteristic of 000 times, excessive voltage and excessive charging current,
When the abnormal temperature inside the battery rises due to the reverse connection voltage, the resistance value increases and the current is limited, and after the temperature abnormality is removed, it returns to the normal resistance value and the battery can be reused, so it is widely used. Has become.

[0007]

However, since the resistivity of the polyswitched PTC element at room temperature is about 1 Ω · cm, the internal resistance of the battery increases, causing an output loss and deteriorating the discharge characteristics. This may cause the life of the device to be shortened. Particularly, when the PTC device is mounted on a large battery, current concentration tends to occur inside the device due to an increase in the area of the device, thereby generating heat.
It is difficult to attach to large batteries. In addition, since polyswitches are generally expensive and large-sized ones are not manufactured, there is a strong demand for a low-cost, low-resistance current control element that is compatible with large batteries.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of such problems of the prior art. According to the present invention, there is provided a composite comprising lithium (Li) and cobalt (Co) as main components. In a lithium secondary battery using a metal oxide as a positive electrode active material and a carbonaceous material as a negative electrode active material, a member made of a shape memory alloy that expands and contracts at an arbitrarily set temperature is mounted as an element for a current interruption mechanism. A lithium secondary battery comprising a mechanism is provided.

Further, in the lithium secondary battery of the present invention, the safety mechanism has an internal terminal connected to a power generation unit of the lithium secondary battery and an external terminal for extracting electricity to the outside. A member made of a shape memory alloy is fitted between the external terminals, and during normal operation of the lithium secondary battery, both terminals are electrically connected,
At the time of abnormal temperature rise of the lithium secondary battery, the shape memory alloy member is deformed to release the electrical connection between the two terminals, for example, as a part connecting the external terminal and the internal terminal, a rod shape, a coil shape, Alternatively, it is preferable to use a shape memory alloy member such as a leaf spring. By adopting such a structure, the shape memory alloy member expands and contracts due to the shape memory effect, so that when the battery temperature exceeds a certain shape memory set temperature due to abnormal temperature rise, conduction between the external terminal and the internal terminal is performed. Is instantaneously cut off, and when the abnormality is cleared, the external terminal and the internal terminal are short-circuited again, so that there is a remarkable effect that the battery can be reused.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in the safety mechanism for a lithium secondary battery of the present invention, since the shape memory alloy member itself is a metal, the resistivity is small, and particularly in the case of a large battery. However, since current concentration hardly occurs, stable battery characteristics can be obtained. Further, since the operation of the element is performed instantaneously, discharge (spark) does not occur at the contact portion between the internal terminal and the element, and it is possible to prevent an increase in contact resistance of the contact portion due to the spark and decomposition of the electrolytic solution. Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, and shows a state where a battery is operating normally.
The power generation unit 2 is connected to an internal terminal 4 having a pressure release hole 5 by a lead wire 3, and the internal terminal 4 is electrically connected to a pressure switch plate 7 having a rupture groove 9 by a contact B,
Further, the pressure switch plate 7 is a current-carrying plate 8 having a pressure release hole 5.
Current interrupting element 30 connected to external terminal 15 through
And at the contact A. The current interruption element 30
The shape memory alloy coil 11 is mechanically joined (caulked, screwed, etc.) between the conducting plate 10 and the external terminal fixing plate 16 with the support rod 14 as a central axis, and further, the internal resistance of the battery is reduced as much as possible. As a device, a copper wire 13 is welded between the current-carrying plate 10 and the external terminal fixing plate 16, and the external terminal fixing plate 16 is welded to the center of the inner surface of the external terminal 15. However, the copper wire 13 can be omitted by using a metal member for the support rod 14.
Further, between the internal terminal 4 and the pressure switch plate 7 and between the internal
Between the insulator 6 and the insulator 12 so that the contacts B and A are insulated when the contacts B and A are separated.
, All of which are housed in the battery case 1.

As shown in FIG. 11, a more detailed configuration of the power generation unit 2 is such that a positive electrode 50 and a negative electrode plate in which a negative electrode 51 and a negative electrode lead 52 are integrated are wound with a separator 53 interposed therebetween. The battery case 1 is made of metal so that the positive electrode 50 is not conducted through the battery case 1 by the insulating plate 54.
, While the negative electrode lead 52 is connected to the inner surface of the battery case 1. The electrolyte is filled in the electrode winding part,
Further, the structure is such that the negative electrode plate and the lead wire 3 are not in contact with each other by the insulating plate 55.

The positive electrode active material of the lithium secondary battery of the present invention is usually lithium cobalt oxide (Li).
A composite oxide containing lithium and cobalt as main components such as CoO ₂ ) is used, a carbonaceous material such as graphite or hard carbon is used as a negative electrode active material, and hexafluorophosphoric acid is used as an organic solvent in an organic solvent. A material in which a lithium electrolyte is dissolved is mainly used.

The conductive members such as the internal terminal 4, the pressure switch plate 7, the conductive plate 8, the external terminal 15, the conductive plate 10, and the external terminal fixing plate 16 used in the present embodiment include:
Copper, which has a small electric resistance, is easy to process and is inexpensive, is preferably used, but nickel or a nickel-copper alloy can also be used. Further, the insulator 6 is preferably in the form of a sheet,
Insulating plastics or the like that are easy to process are preferably used, but those having a melting point equal to or higher than the operating temperature of the shape memory alloy coil 11 are preferable from the viewpoint of durability. In addition, since the insulator 12 needs to have a thickness corresponding to the length of the shape memory alloy coil 11, when a soft insulating member is used, the insulator is insulated when crimped and stored in the battery case 1. When an insulating plastic is used, a hard member is preferable, since the member 12 may be deformed and may not be able to hold each structural member in a fixed position.
Insulating ceramic members such as alumina and zirconia can also be suitably used.

FIG. 2 shows the state of the embodiment of the present invention shown in FIG. 1 in which the battery temperature rises for some reason, such as overcurrent due to external terminal short circuit or overcharge due to abnormal charging, and the current cutoff element 30 is activated. FIG. When the current cutoff element 30 becomes higher than the shape memory temperature of the shape memory alloy coil 11, the shape memory alloy coil 11 contracts instantaneously, the contact A is separated, and the current is cut off. Therefore, unlike the conventional PTC element, the current is completely cut off instantaneously, so that an abnormal situation can be promptly dealt with, so that reliability and safety can be improved. Furthermore,
In the present embodiment, the temperature rise due to charge and discharge is too rapid despite the interruption of the current, the exothermic reaction continues for a certain period of time after the interruption of the current, and the internal pressure of the battery further increases It is preferable to mount a conventional safety mechanism for releasing the internal pressure of the battery by rupture of the built-in rupture groove 9.

FIG. 3 shows an embodiment in which the shape memory alloy coil 17 of the current cutoff element 31 extends beyond the normal state and cuts off the current at a temperature higher than the shape memory set temperature, and FIG. 3 shows a state in which the current interrupting element 31 is activated in the embodiment shown in FIG. This safety mechanism operates in the same manner as the safety mechanism in FIGS. 1 and 2 described above. However, in the present embodiment, the copper wire 13 shown in FIG. 1 is not mounted. this is,
When the current interrupting element 31 operates and returns to the normal state again, there is no case where the copper wire 13 is sandwiched between the conductive plate 8 and the shape memory alloy coil 17 so that the contact A is not formed well. However, the shape memory alloy coil 17 is a good conductor because it is made of metal, and the use of a metal member for the support rod 14 causes no practical problem.

FIG. 5 is a sectional view showing another embodiment of the present invention. In the present embodiment, a leaf spring-shaped shape memory alloy member 18 is mechanically joined (caulked, screwed, etc.) between the conducting plate 10 having the pressure release holes 5 and the external terminal fixing plate 16. Current interrupting element 32,
The current interrupting element 32 is connected to the pressure switch plate 7 through the contact C.
Is in contact with The mode of operation in this case conforms to the embodiment shown in FIG. Also in this embodiment, since the cross-sectional area of the leaf spring-shaped shape memory alloy member 18 is generally larger than that of the coil and is a good conductor, the copper wire 13 as shown in FIG. There is little need to do this.
The shape memory alloy coil 1 in which the direction of expansion and contraction of the shape memory alloy coil 11 is opposite to that of the embodiment shown in FIG.
As in the embodiment of FIG. 3 using No. 7, it is needless to say that an embodiment in which the expansion and contraction direction of the shape memory alloy leaf spring 18 is the opposite direction is also conceivable in this embodiment.

FIG. 6 shows an embodiment showing a safety mechanism using a current interrupting element 33 comprising a shape memory alloy coil 11 and a metal plate 19 having spring properties. The metal plate 19 having the spring property is connected to the internal terminal 4 at the contact D, and the contact E between the shape memory alloy coil 11 and the metal plate 19 having the spring property is formed by contact. Reference numeral 11 also serves as a current path.

FIG. 7 shows a state in which the safety mechanism in the embodiment shown in FIG. 6 is operated. That is, when the internal pressure of the battery rises, the metal plate 1 having a spring property is generated by the internal pressure.
9 bends and the contact D separates instantaneously, interrupting the current. In this state, if the cause of the abnormality is removed, the contact point E between the metal plate 19 having a spring property and the shape memory alloy coil 11 is maintained in a connected state, and when the internal pressure returns to the normal state, the shape memory alloy The bent portion of the metal plate 19 having the spring property returns to the original state by the expansion and contraction force of the coil 11, the contact D is formed again, and the battery can be reused. However, even if the current is cut off at the contact point D, if the temperature of the current cutoff element 33 further rises and reaches the shape memory temperature of the shape memory alloy coil 11, the shape memory alloy coil 11 It contracts further by the memory action, and the contact E
Also leave. By the operation of these safety mechanisms, when the cause of the abnormality is eliminated and the internal pressure of the battery returns to the normal state, or when the temperature becomes equal to or lower than the shape memory temperature of the shape memory alloy coil 11, the contacts D and E are set. The battery is formed again, but at this time, the battery cannot be reused unless both contacts are formed. That is, the safety mechanism is provided with both a pressure switch based on contact / non-contact of the contact D and a temperature switch based on contact / non-contact of the contact E, thereby further ensuring safety. Further, unlike the conventional pressure switch, since the current is instantaneously interrupted, a discharge phenomenon (spark) does not occur at the contact point D and the electrolytic solution is not adversely affected. However, in the event of an abnormality in which the internal pressure of the battery rises despite the operation of these two current interrupting elements, the rupture groove 9 bursts and the internal pressure is released, and in this case, the battery cannot be reused. .

FIG. 8 is a sectional view of an embodiment in which the embodiment shown in FIG. 1 and the embodiment shown in FIG. 6 are combined. In the case of the present embodiment, the spring 20 in contact with the metal plate 19 having the spring property does not need to be a shape memory alloy as shown in the embodiment of FIG. Because the springy metal plate 19 is in direct contact with the current-carrying plate 8, it is not necessary to cut off the current by the contact F between the springy metal plate 19 and the spring 20, and the spring 20 is simple. This is because it is only necessary to have a function of re-forming the contact D that is farther away from the target. That is, in the present embodiment, a current interrupting mechanism that operates in response to an increase in the temperature of the battery and a current interrupting mechanism that operates in response to an increase in the internal pressure of the battery are mounted to ensure safety. Further, in the case where the battery body is deformed by applying an external stress and the internal pressure continues to rise, the contact D is separated and cannot be used, so that it is possible to avoid erroneous use of the defective battery. .

The operation mode of the safety mechanism according to the present embodiment is as follows. First, when the battery temperature rises due to charging / discharging abnormality or operating environment, since the battery body has a hermetically sealed structure, as shown in FIG. The contact D is bent and cuts off the current. However, when the cause of the abnormality is removed, the battery temperature drops to the normal temperature, and the battery internal pressure returns to the normal value,
The contact D is re-formed by the expansion and contraction force of the spring 20, and the electricity can be supplied. However, when the temperature continues to rise despite the interruption of the current due to the separation of the contact D, as shown in FIG. 9, the shape memory alloy element 30 also operates, and the contact A is separated. That is, in this case, since the current interruption points in the battery are two places, both the release of the abnormality of the battery internal pressure by re-forming the contact D and the release of the temperature abnormality by re-forming the contact A are performed. Without it, the batteries cannot be reused. Of course, if the internal pressure of the battery rises despite the operation of these two safety mechanisms, a conventional safety mechanism in which the rupture groove 9 ruptures to release the internal pressure is also provided in parallel.

The embodiments of the present invention have been described in detail above, but it goes without saying that the present invention is not limited by these embodiments. In addition, it is understood that various changes, modifications, improvements, and the like can be made to the present invention based on the knowledge of those skilled in the art without departing from the spirit of the present invention in addition to the above-described embodiments. Should.

[0023]

As described above, according to the lithium secondary battery equipped with the safety mechanism using the shape memory alloy member of the present invention, the shape memory alloy member itself used for the safety mechanism is metal. Therefore, there is an advantage that a stable battery characteristic can be obtained because the current concentration is unlikely to occur even in the case of a large-sized battery having a low resistivity. In addition, since the operation of the current interrupting element using a metal plate having a spring property is performed instantaneously, no discharge (spark) occurs at the contact portion between the internal terminal and the current interrupting element, and the contact portion due to the spark is not generated. The contact resistance is increased, and the decomposition of the electrolytic solution is prevented, so that a remarkable effect of preventing a charge / discharge accident can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an insulation operation state of the embodiment shown in FIG. 1 of the present invention.

FIG. 3 is a cross-sectional view showing another embodiment of the present invention.

FIG. 4 is a cross-sectional view showing an insulation operation state of the embodiment shown in FIG. 3 of the present invention.

FIG. 5 is a sectional view showing still another embodiment of the present invention.

FIG. 6 is a cross-sectional view of yet another embodiment of the present invention.

FIG. 7 is a cross-sectional view showing an insulation operation state of the embodiment shown in FIG. 6 of the present invention.

FIG. 8 is a sectional view showing still another embodiment of the present invention.

FIG. 9 is a cross-sectional view showing an insulation operation state of the embodiment shown in FIG. 8 of the present invention.

FIG. 10 is a sectional view of a conventional safety mechanism for a lithium secondary battery.

FIG. 11 is a structural diagram of a power generation unit of the lithium secondary battery of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Battery case, 2 ... Power generation part, 3 ... Lead wire, 4 ... Internal terminal, 5 ... Pressure relief hole, 6 ... Insulator, 7 ... Pressure switch plate,
Reference numeral 8: conductive plate, 9: burst groove, 10: conductive plate, 11: shape memory alloy coil, 12: insulator, 13: copper wire, 14: support rod, 15: external terminal, 16: external terminal fixing plate, 17 ... shape memory alloy coil, 18 ... leaf spring shape memory alloy member (shape memory alloy leaf spring), 19 ... metal plate having spring property,
20: spring, 21: PTC element, 30: current cutoff element,
31 current interrupting element, 32 current interrupting element, 33 current interrupting element, 50 positive electrode, 51 negative electrode, 52 negative electrode lead, 53 separator, 54 insulating plate, 55 insulating plate,
A: contact point between the current interrupting element (30, 31) and the conducting plate 8,
B: contact point between the internal terminal 4 and the pressure switch plate 7, C ... contact point between the current interrupting element 32 and the pressure switch plate 7, D ... contact point between the internal terminal 4 and the metal plate 19 having spring properties, E ... shape memory Contact point between the alloy coil 11 and the metal plate 19 having spring property, F
... Point of contact between spring 20 and metal plate 19 having spring properties

Claims (3)

[Claims] 1. A lithium secondary battery in which a composite metal oxide containing lithium (Li) and cobalt (Co) as main components is used as a positive electrode active material and a carbonaceous material is used as a negative electrode active material. A lithium secondary battery comprising a safety mechanism in which a member made of a shape memory alloy that expands and contracts at a temperature is mounted as an element for a current interruption mechanism. 2. The safety mechanism has an internal terminal connected to a power generation unit of the lithium secondary battery, and an external terminal for extracting electricity to the outside, and has a shape memory between the internal terminal and the external terminal. A member made of an alloy is inserted, and both terminals are electrically connected at the time of normal operation of the lithium secondary battery, and at the time of abnormal temperature rise of the lithium secondary battery, the shape memory alloy member is deformed. 2. The lithium secondary battery according to claim 1, wherein the electrical connection between both terminals is released. 3. The device according to claim 1, wherein said shape memory alloy member is formed in a rod shape, a coil shape or a leaf spring shape.
Or the lithium secondary battery according to 2.