JP2003151640A - Secondary battery protecting element and installation method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery protecting element series-connected to a secondary battery to trip a PTC element limiting short-circuit current on other control current and thereby to cut off a charging and discharging circuit. SOLUTION: One face of the PCT element 25 is bonded to a first electrode plate 21, and the other face thereof is bonded to a second electrode plate 22 and a third electrode plate 23. The secondary battery is series connected between the first electrode plate 21 and second electrode plate 22, and the short- circuit current trips the PTC element to protect the secondary battery when a short circuit occurs. By applying the control current between the third electrode plate 23 and the first electrode plate 21 or second electrode plate 22 to trip the PTC element 25, the charging and discharging circuit of the secondary battery is cut off. Therefore, the PTC element 25 is also used for protecting the secondary battery from overcharging or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention also provides a PTC element provided to protect a secondary battery such as a lithium ion secondary battery from an external short circuit, and also has a purpose of protecting the secondary battery from overcharge and overdischarge. The present invention relates to a secondary battery protection element that can be used together.

[0002]

2. Description of the Related Art PTC elements are "PTC: Positi"
ve Temperature Coefficien
It is a type of thermistor having “nt = positive temperature coefficient” and is a thermal device having a positive characteristic. It has a characteristic that the temperature rises due to overcurrent or overheating, and when the temperature exceeds a certain temperature, the resistance value sharply rises. It is used for the purpose of protecting the secondary battery from an external short circuit by utilizing this characteristic.

In a relatively large lithium-ion secondary battery, a disk-type PTC element is provided inside the sealing portion that seals the opening of the battery can, and a metal object or a circuit failure may occur between the positive electrode and the negative electrode of the battery. When an external short circuit occurs, self-heating occurs due to an excessive short-circuit current, and the short-circuit current is limited by a sharp increase in resistance value accompanying temperature rise, thereby preventing a battery from bursting or other troubles due to an external short circuit. Further, in a relatively small lithium-ion secondary battery for a portable device or the like, a PTC element is provided inside a pack case together with a protection circuit for protecting the battery from overcharge, overdischarge, etc., and is configured in the form of a battery pack. . Even in this case, as in the previous case, when the PTC element is externally short-circuited between the positive electrode and the negative electrode of the battery pack due to a metal object, a circuit failure, or the like, an excessive short-circuit current causes self-heating, and the resistance value rapidly increases with a temperature rise. Limits the short-circuit current and prevents the battery from being damaged by an external short-circuit. As described above, in a battery having a high energy density such as a lithium-ion secondary battery or a nickel-hydrogen storage battery, it is a well-known technique to provide a PTC element to cope with an external short circuit and to configure a battery circuit.

FIG. 5 shows a PTC element 51 and a protection circuit 58.
FIG. 1 is a circuit diagram showing a configuration of a battery pack using. The protection circuit 58 is provided to protect the secondary battery 52 from overcharge, overdischarge, and overcurrent, and includes a voltage detection unit 53 and first and second operations controlled by the voltage detection unit 53. Each of the FETs 54 and 55 is provided. The voltage detection unit 53 determines the battery voltage in the charged state and the discharged state of the secondary battery 52 and the first and second FETs.
When the load current is detected from the voltage between 54 and 55 and the battery voltage corresponding to the overcharged state or the overdischarged state or the excessive load current is not detected, the first and second FETs 54 and 55 are turned on. Control the state. Since the first and second FETs 54 and 55 are connected in series with the secondary battery 52, a charging / discharging circuit of the secondary battery 52 is formed in the conductive state. When the battery voltage corresponding to the overcharged state is detected, the voltage detection unit 53 controls the first FET 54 so as to be in the cutoff state, and when the battery voltage corresponding to the overdischarged state is detected, the second voltage detection unit 53 The FET 55 is controlled to be in the cutoff state. In addition, the voltage detector 53
The load current is detected from the voltage between the source and the drain of the second FET 55, that is, the voltage drop due to the on-resistance of the second FET 55, and an excessive value occurs when the positive terminal 56 and the negative terminal 57 are short-circuited. When the load current is detected, the first and second FETs 54 and 55 are controlled to be in the cutoff state to protect the secondary battery 52 from overcurrent.

When the overcurrent protection function of the protection circuit 58 does not operate normally, the secondary battery 52 is exposed to an excessive load current such as a short-circuit current, and gas is expelled due to temperature rise, leading to rupture. There is a fear. In order to doubly protect the secondary battery 52 from this overcurrent, the PTC element 51 is connected in series with the secondary battery 52, and during normal times the low resistance value interferes with charging / discharging of the secondary battery 52. However, if the positive electrode terminal 56 and the negative electrode terminal 57 of the battery pack are short-circuited by a metal object or the device connected to this battery pack is short-circuited, the secondary battery 5
The short-circuit current from 2 self-heats, and when the temperature reaches a predetermined temperature, the resistance value suddenly increases, and the short-circuit current is limited. Since the resistance value change when the PTC element 51 is in the trip state is 10 4 to 6 power, the secondary battery 52 is reliably prevented from being damaged by an external short circuit.

With the above structure, the secondary battery 52 is protected so as not to be damaged by overcharge, overdischarge, or an external short circuit. However, when the protection circuit 58 does not operate normally for some reason, the secondary battery 52 will be damaged by overcharging or overdischarging. Particularly, since overcharging significantly deteriorates the battery, it is necessary to reliably protect the secondary battery from overcharging. The applicant of the present application has proposed, as Japanese Patent Application No. 11-135325, a battery protection circuit that uses a PTC element to doubly protect a secondary battery from overcharging.

FIG. 6 shows the structure of a battery protection circuit that double protects the secondary battery from overcharging. The secondary battery 5 is thermally coupled to the first PTC element 11 connected in series. Composite PTC in which the second PTC element 12 is arranged in a closed state
The element 10 is provided. The first voltage detection unit 1 has the same configuration as the voltage detection unit 53 in the above configuration, and when the battery voltage corresponding to the overcharged state or the overdischarged state is detected, the first FET 7 or the second FET 8 Is controlled to a cutoff state to cut off the charging / discharging circuit of the secondary battery 5 to protect the secondary battery 5 from overcharge and overdischarge. In addition, the first voltage detection unit 1 detects the load current from the drain-source voltage of each of the second FETs 8, that is, the voltage drop due to the on-resistance of the second FET 8, and the positive electrode terminal 15 and the negative electrode terminal 16 are connected. When an excessive load current is detected when a short circuit occurs between the first FET 7 and the second FET 8
Is controlled to a cutoff state to protect the secondary battery 5 from overcurrent.

When the first voltage detector 1 falls into a state where it does not operate normally, the overcharged state cannot be prevented and the battery voltage rises. At this time, the second voltage detection unit 2 detects the battery voltage in the overcharged state and controls the third FET 3 to be in the conductive state. When the third FET 3 becomes conductive, the second PTC becomes
Since a current flows through the element 12, the second PTC element 12 rises in temperature and is thermally coupled to the first PTC element 11.
To heat. When the temperature of the first PTC element 11 reaches a temperature at which the first PTC element 11 is in a trip state due to this heating, the first PTC element 11
Since the element 11 greatly limits the charging current to the secondary battery 5 due to the rapid increase of the resistance value, the secondary battery 5 is released from the continuation of the overcharged state.

As shown in FIG. 7, the composite PTC element 10 in which at least two PTC elements 11 and 12 are heat-coupled and integrated as described above has two PTC elements 11a and 12a connected to the electrode plate 19, as shown in FIG. , 20, 21 are sandwiched and integrated to form each electrode plate 19, 20, 2
The lead 19a, 20a, 21a may be pulled out from the lead wire 1.

[0010]

In the structure in which the two PTC elements shown in the above-mentioned prior art are integrated by sandwiching the PTC elements between the electrode plates, it is necessary to use two PTC elements. There was a problem of cost increase and volume increase.
It is an indispensable requirement as a battery power source for portable electronic devices that the protective element be integrated with a secondary battery to be made compact.
There is a demand for a protection element that is smaller and operates reliably.

The present invention was devised in view of the above-mentioned problems of the conventional structure, and a secondary device in which the protection element is composed of one PTC element, and the thermal conductivity is improved, the size and the simplification are reduced, and the cost is reduced. It is an object to provide a battery protection element.

[0012]

[MEANS FOR SOLVING THE PROBLEMS] A secondary battery protection device according to the first invention of the present application for achieving the above object is one PT.
It is characterized in that at least three electrode plates are joined to the C element. If a pair of electrode plates of this secondary battery protection element is connected in series to the secondary battery, when an overcurrent such as a short-circuit current flows in the secondary battery, the PTC element rises in temperature and the resistance value rapidly increases. The secondary battery is protected by limiting. When a current is applied to the PTC element from another electrode plate, the temperature of the PTC element rises and the resistance value rapidly increases, so that the charge / discharge circuit of the secondary battery is cut off.
Therefore, this secondary battery protection element can open and close the charging / discharging circuit by a control current in addition to protection from an external short circuit of the secondary battery. When overcharge is detected and the control current is passed, the charging / discharging circuit is opened. Will be shut off and can be used together for the purpose of protecting the secondary battery.

In the secondary battery protection element according to the second aspect of the present invention, the PTC element is formed in a plate shape, the first electrode plate is joined to one surface of the PTC element, and the second electrode is attached to the other surface. It is characterized in that the plate and the third electrode plate are joined together. This secondary battery protection element has a first electrode plate and a second electrode plate.
If the secondary battery is connected in series with the electrode plate of, the PTC element will rise in temperature and rapidly increase the resistance value when an overcurrent such as a short-circuit current flows in the secondary battery. The secondary battery is protected. Further, when a current is made to flow from the third electrode plate to the PTC element, the temperature of the PTC element rises and the resistance value rapidly increases, so that the charging / discharging circuit of the secondary battery is cut off. Therefore, this secondary battery protection element can open and close the charging / discharging circuit by the control current from the third electrode plate in addition to protection from the external short circuit of the secondary battery, and detect the overcharge to detect the control current. When the current flows, the charging / discharging circuit is cut off and can be used for the purpose of protecting the secondary battery from overcharging.

In the secondary battery protection device, leads for surface mounting on the circuit board are formed to extend from the first electrode plate, the second electrode plate, and the third electrode plate on the same plane. The PTC element can be surface-mounted on the circuit board by being formed so as to extend outside from the projected area in the circuit board mounting direction, and the surface-mounted by extending outside the projected area. The secondary battery protection element can be reliably soldered to the circuit board.

Further, in the secondary battery protection element according to the third invention of the present application, the PTC element is formed in a chip shape, and the first electrode plate and the second electrode plate are joined to the facing surface of the chip-shaped PTC element. A third electrode plate is joined to a surface intersecting with the facing surface. The operation of this secondary battery protection element is the same as that of the above-mentioned second aspect of the invention, but since it is formed in the shape of a chip, it can be miniaturized and mounted on a circuit board by a component mounter easily.

In the above structure, the first electrode plate, the second electrode plate, and the third electrode plate are formed such that their respective end portions are located on the substrate mounting surface and are raised from it.
Soldering of each electrode plate to the land on the circuit board is surely performed.

The method of mounting the secondary battery protection element according to the fourth invention of the present application is such that at least three PTC elements are provided in one PTC element.
A secondary battery protection element formed by joining two electrode plates is characterized in that each electrode plate is connected to a predetermined position by wiring and is thermally coupled to the secondary battery via a heat conductive material. With this mounting method, the secondary battery protection element operates to perform short-circuit protection that shuts off the secondary battery charge / discharge circuit due to short-circuit current, and battery protection that shuts off the secondary battery charge / discharge circuit when overcharge is detected. In addition to the above operation, when the temperature of the rechargeable battery is abnormally increased due to being thermally coupled to the rechargeable battery, the charge / discharge circuit is shut off and the rechargeable battery in the high temperature state cannot be used. Is possible.

In the above mounting method, the circuit board on which the secondary battery protection element is mounted is mounted on the circuit board by arranging the secondary battery protection element in contact with the secondary battery with a heat conductive material interposed. Then the wiring to each electrode plate is made,
The secondary battery protection device can be thermally coupled to the secondary battery.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention.
The embodiments described below are examples of embodying the present invention and do not limit the technical scope of the present invention.

The present embodiment shows a secondary battery protection element constructed for the purpose of protecting a lithium ion secondary battery from an external short circuit, overcharge, overdischarge or the like. The secondary battery protection element is configured by joining at least three electrode plates to one PTC element formed of a conductive polymer.

FIG. 1 shows the structure of a secondary battery protection element A according to the first embodiment, in which one surface of a PTC element 25 formed of a conductive polymer in a plate shape has a first electrode plate 21. Are joined, and the second electrode plate 22 and the third electrode plate 23 are joined to the other surface.

A conductive poly that forms the PTC element 25.
Is a polymer that is an insulator and carbon that is a conductor.
Resistor compounded in a prescribed ratio, with moderate conductivity and positive temperature
It shows the characteristics. In the polymer at room temperature
Low because dispersed carbon forms innumerable conductive paths
Although it is a resistance value, when the temperature rises, the thermal expansion of the polymer causes
The conductive path of carbon is gradually cut,
The resistance value of the crab increases to the temperature at which the polymer melts.
When this happens, the polymer undergoes a large volume change and
The resistance value is suddenly changed due to a trip condition that disconnects the conductive path.
To 10^Four-10 ⁶It doubles. Temperature of PTC element 25
The degree of self-heating caused by a large current or external
It rises due to heating and heat conduction from.

The first to third electrode plates 21 to 23 are joined to the PTC element 25, and the first to third electrode plates 21 to 2 are joined.
Leads 21 for connecting from 3 to the circuit board, respectively
a, 22a, and 23a are pulled out. In order to allow the secondary battery protection element A to be surface-mounted on the circuit board, the leads 21a, 22a, and 23a are located outside the projected area of the secondary battery protection element A in the board mounting direction, and each tip portion is the same. It is formed so as to be located on a plane.

The secondary battery protection element A is mounted at a predetermined position on the circuit board forming the battery protection circuit shown in FIG. As shown in FIG. 3, in the circuit board 30 on which the secondary battery protection element A is mounted, the secondary battery protection element A is in contact with the battery can 35 of the secondary battery 5 via the silicon bond (high thermal conductive material) 33. The secondary battery protection element A and the secondary battery 5 are thermally coupled to each other.

In FIG. 2, the first part of the secondary battery protection element A is shown.
The electrode plate 21 is connected to the positive electrode input / output terminal 15, the second electrode plate 22 is connected to the positive electrode of the secondary battery 5, and the third electrode plate 23 is connected.
Is connected to the third FET 3. Since the first electrode 21 and the second electrode 22 of the secondary battery protection element A are connected in series to the secondary battery 5, a metal object contacts between the positive electrode input / output terminal 15 and the negative electrode input / output terminal 16 to cause a short circuit. When it becomes a state,
When a short circuit occurs due to a failure of equipment connected to the positive electrode input / output terminal 15 and the negative electrode input / output terminal 16, the PTC
The element 25 self-heats due to a short-circuit current, and when its temperature exceeds, for example, 80 ° C., the resistance value, which is 0.02Ω or less at room temperature, suddenly changes 10 ⁴ to 10 ⁶ times. Due to the rapid increase in the resistance value, the short-circuit current is limited, and the secondary battery 5 can be prevented from being damaged by the short circuit.

The first voltage detector 1 monitors the voltage of the secondary battery 5 and normally conducts when the battery voltage exceeds a preset charge stop voltage in the charged state of the secondary battery 5. The first FET 7 in the state is controlled to the cutoff state,
The charging circuit of the secondary battery 5 is cut off to prevent the secondary battery 5 from falling into an overcharged state. In addition, when the battery voltage falls below a preset discharge stop voltage in the discharged state of the secondary battery 5, the second FET 8 which is normally in the conductive state is controlled to be in the cutoff state, and the discharge circuit of the secondary battery 5 is turned on. It is cut off to prevent the secondary battery from falling into an over-discharged state.

A second voltage detector 2 is provided in case an abnormality occurs in the control operation for preventing overcharge by the first voltage detector 1. If the charge stop voltage is not detected due to the failure of the first voltage detection unit 1 or the first FET 7 or the charge / discharge circuit cannot be cut off, the charging is continued and the charging is continued. The voltage of the secondary battery 5 increases. The second voltage detection unit 2 controls the third FET 3, which is normally in the cutoff state, to the conductive state when the second charge stop voltage exceeding the preset charge stop voltage is detected. Due to the conduction of the third FET 3, a large current flows from the positive electrode input / output terminal 15 to the third electrode 23 through the first electrode 21 of the secondary battery protection element A, so that the temperature of the PTC element 25 rises and a short circuit current flows. Similarly to the case, the inflow of the charging current into the secondary battery 5 is limited by the rapid increase in the resistance value due to self-heating. Therefore, a double overcharge protection function is configured to prevent the secondary battery 5 from being damaged by continuing the overcharged state.

Further, since the secondary battery protection element A is arranged in a state of being thermally coupled to the secondary battery 5 as described above,
When the temperature of the secondary battery 5 abnormally rises due to an internal short circuit or the like, the resistance value is rapidly increased by heat conduction from the secondary battery 5, and the input / output current of the secondary battery 5 is limited to cause abnormal heat generation. It protects the battery 5 from being charged or discharged. Further, since the secondary battery protection element A is also affected by the ambient temperature, it is possible to limit the use of the secondary battery 5 in a state where the environmental temperature is high. For example, when the battery pack or a device equipped with the battery pack is left in a car parked under the scorching sun in midsummer, the battery temperature may exceed 80 ° C. In such a case, since the secondary battery protection element A has an increased resistance value, the secondary battery 5 cannot be used, and it is possible to prevent the secondary battery 5 from being used in an abnormal temperature state. Since the resistance value of the secondary battery protection element A returns to the original low value when the environmental temperature decreases, it can be returned to the normal usable state.

The secondary battery protection element A described above has three electrode plates 21 for the PTC element 25 formed in a plate shape.
This is an example in which 22 and 23 are joined, but a chip-type secondary battery protection element B as shown in FIG. 4 can also be used.

In FIG. 4, a PTC formed in a chip shape
The first electrode plate 41 and the second electrode 41 are provided on the opposite surface of the element 40.
The electrode plate 42 is joined, and the third electrode plate 43 is joined to the surface orthogonal to the facing surface. First to third electrode plates 41 to 4
3 has its end portion formed on a vertical surface located on the board mounting surface so that the secondary battery protection element B can be reliably soldered when it is surface-mounted on the circuit board.

The secondary battery protection elements A and B described above are
Three electrode plates 21 for one PTC element 25, 40
-23, 41-43 are joined to form a three-terminal type,
It is also possible to join four electrode plates to one plate-shaped or chip-shaped PTC element to form a four-terminal type secondary battery protection element. In such a secondary battery protection device, the change in the resistance value of the PCT device between the two electrode plates can be controlled individually from the other two electrode plates, so that the interruption of the input / output circuit of the secondary battery is caused by two factors. Can be controlled.

Although the present invention is intended to protect the secondary battery from a short circuit or overcharge, it can be applied to the protection operation of other electric circuits.

[0033]

As described above, according to the present invention, the PTC element which is connected in series to the charging / discharging circuit of the secondary battery and trips by the short-circuit current to protect the secondary battery is provided with a device other than the charging / discharging current. Since it can be tripped under control conditions, it can be used together for the purpose of protecting the secondary battery from overcharging.

[Brief description of drawings]

FIG. 1A is a plan view and FIG. 1B is a side view showing a configuration of a secondary battery protection element according to a first embodiment.

FIG. 2 is a circuit diagram of battery protection to which the same element is applied.

FIG. 3 is a partial side view showing a method of mounting the same element.

FIG. 4 is a perspective view showing a configuration of a secondary battery protection element according to a second embodiment.

FIG. 5 is a circuit diagram showing a basic configuration of a battery protection circuit.

FIG. 6 is a circuit diagram of a battery protection circuit provided with a double protection structure.

FIG. 7 is a side view showing the configuration of a conventional protection element.

[Explanation of symbols]

A, B secondary battery protection element 5 secondary battery 25, 40 PTC element 21, 41 First electrode plate 22, 42 Second electrode plate 23, 43 Third electrode plate 30 circuit board 33 Silicon bond (high thermal conductivity material)

Claims (8)

[Claims] 1. A secondary battery protection device comprising at least three electrode plates joined to one PTC device. 2. A PTC element is formed in a plate shape, and this PT
A secondary battery protection element, characterized in that the first electrode plate is joined to one surface of the C element, and the second electrode plate and the third electrode plate are joined to the other surface. 3. The secondary according to claim 2, wherein leads for surface mounting on the circuit board are formed to extend from the first electrode plate, the second electrode plate, and the third electrode plate on the same plane. Battery protection element. 4. The secondary battery protection element according to claim 3, wherein the lead is formed so as to extend outward from a projected area of the secondary battery protection element in the circuit board mounting direction. 5. The PTC element is formed in a chip shape, the first electrode plate and the second electrode plate are joined to the facing surface of the chip PTC element, and the third electrode plate is provided on the surface intersecting with the facing surface. A secondary battery protection element characterized by being joined. 6. The secondary electrode according to claim 4, wherein each of the first electrode plate, the second electrode plate, and the third electrode plate is formed on a surface of which a respective end portion is located on the substrate mounting surface and rises therefrom. Battery protection element. 7. A secondary battery protection device comprising at least three electrode plates joined to one PTC device, each electrode plate being connected to a predetermined position by wiring, and a secondary battery via a heat conductive material. A method for mounting a secondary battery protection element, characterized in that it is thermally bonded to the secondary battery. 8. The secondary battery according to claim 7, wherein the circuit board on which the secondary battery protection element is mounted is arranged so that the secondary battery protection element is in contact with the secondary battery with a heat conductive material interposed therebetween. How to install the protective element.