JP2002298829A - Protective element for electrochemical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective device for an electrochemical device, with simple construction, requiring little load on a circuit and having no constraint on the mounting position and permitting accurate operation, even under overvoltage condition. SOLUTION: The protecting element for the electrochemical device as a protective element for protecting an electrochemical element comprises a varistor VZ and a heat-sensitive protecting element TF bonded thermally to each other, the heat-sensitive protective element TF operating due to the temperature rise of the varistor VZ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective element for an electrochemical device such as a polymer lithium secondary battery and an electric double layer capacitor, and more particularly to a safety mechanism against heat generation in an abnormal condition.

[0002]

2. Description of the Related Art Due to the remarkable development of portable devices in recent years,
The importance of batteries used as power supplies for portable devices, especially lithium ion batteries, is increasing rapidly. Further, with the increase in the functions of portable devices, the goal of technological development is to increase the energy, thereby improving the battery characteristics and safety.

Specifically, the following items are listed. (1) Improvement of safety (counter measure against overcharge) (2) Improvement of high-temperature storage characteristics (3) Improvement of cycle characteristics

[0004] Among them, with respect to safety, measures are currently being taken to prevent ignition and reduction of explosion at the time of abnormality by installing a protection circuit, a PTC element, a thermal fuse and the like. Especially recently, safety has been improved due to various factors.
Simplification of the protection circuit as described in Technical Report Vol. 53, No. 10, p. 93 is also being studied.

FIG. 6 shows a schematic configuration of a conventional charging circuit using a thermal fuse. This charging circuit includes a rechargeable battery 17
A voltage monitoring unit 11 for monitoring the voltage of the power supply, a current / temperature monitoring unit 12 for monitoring the temperature / current, and an output control unit 1 for controlling the control elements 14 and 15 based on the information.
3 having a primary protection circuit. Further, an interface unit 19 is provided for transmitting and receiving power and information between the primary protection circuit and an external circuit via input / output terminals. And
One of the charging input / output terminals is connected to one end of a secondary battery 17 via a temperature fuse 18, and the other charging / input terminal is connected to the secondary battery 17 via a temperature fuse 16 and control elements 14 and 15. Is connected to the other end. The thermal fuse 18 is thermally connected to the battery 17, and the thermal fuse 16 is thermally connected to the control elements 14 and 15, respectively.

As described above, the battery 17, the charging control element 1
By providing thermal fuses that are thermally coupled to each of 4 and 15, the charging route is cut off when any abnormal heat is generated, thereby improving safety.

Further, as for the fuse described in this simple protection circuit, a type with a built-in resistor has been developed. Although this fuse with a built-in resistor is thermally coupled to the resistor, it needs to be attached to a switching element for energizing the resistor, and there is a restriction on a place where the fuse is attached. That is, the switching element performs charging and discharging by a voltage signal from the protection circuit. In order to operate the fuse at the time of charging, the switching element and the resistance element must be thermally and voltage-coupled. It was necessary to configure a circuit.

FIG. 7 shows a charging circuit using such a fuse with a built-in resistor. In this example, the voltage of the battery 17 is detected in parallel with the voltage monitoring unit 11, and a current is supplied to the resistor 25 via the switching element 22 in accordance with the voltage.
A next protection circuit 21 is added. Other components are the same as those in FIG. 6, and the same components are denoted by the same reference numerals and description thereof will be omitted.

As described above, when the secondary protection circuit 21 detects an abnormal voltage, the resistance 25 is heated to operate the thermal fuse 16, thereby further increasing the safety against abnormal charging.

However, such a configuration complicates the circuit configuration and requires many components. Also,
There is a problem that the mounting location is restricted because the respective elements are thermally coupled.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a protection for an electrochemical device which has a simple structure, has a small load on a circuit, has no restriction on a mounting place, and can operate reliably even in an overvoltage state. It is to provide an element.

[0012]

This and other objects are attained by the present invention described below. (1) A protection element for an electrochemical device as a protection element for protecting an electrochemical device, wherein a varistor and a heat-sensitive protection element are thermally coupled, and the temperature of the varistor rises to activate the heat-sensitive protection element. Element for electrochemical devices. (2) The protection device for an electrochemical device according to (1), wherein the varistor is a multilayer chip varistor. (3) The protection device for an electrochemical device according to the above (1) or (2), wherein the varistor and the heat-sensitive protection element are enclosed in the same case. (4) The varistor and the electrochemical device are connected so that an equivalent circuit is connected in parallel.
Any of the electrochemical devices. (5) The protection device for an electrochemical device according to any one of the above (1) to (4), wherein the electrochemical device is a lithium secondary battery.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A protection element VZ · TF for an electrochemical device according to the present invention is a protection element for an electrochemical device as a protection element VZ · TF for protecting an electrochemical device E as shown in FIG. The varistor VZ and the heat-sensitive protection element TF are thermally coupled to each other,
The heat-sensitive protection element TF operates due to the temperature rise.

That is, the protection element of the present invention does not require a fuse used for overcurrent protection and a switching element that operates on the PTC element. Specifically, a varistor functioning at a low voltage is connected to a fuse or a PTC element, and when the varistor is activated, the fuse or the PTC element is operated by heat generated from the varistor.

The varistor used here mainly has zinc oxide as its main component, and has a resistance which varies non-linearly with voltage. The varistor used in the present invention is desirably a chip-type varistor to facilitate thermal coupling with a fuse or a PTC element.

Normally, the characteristics of a varistor are represented by various parameters defining current-voltage characteristics. In particular, a voltage at which a current of 1 mA flows is called a varistor voltage. Therefore, as the varistor in the present invention, it is necessary to use elements having various varistor voltages depending on the application. In particular,
A voltage of 3 to 40 V, particularly 4 to 15 V is preferred. Further, as the current at the time of operation, it is sufficient that enough heat is generated to operate the heat-sensitive protection element.
About 100 mA, especially about 10 to 30 mA.

As described above, by setting the optimum varistor voltage according to the electrochemical device to be used, it is possible to detect an overvoltage and prevent rupture and ignition. That is, by using a varistor having a varistor voltage corresponding to the overvoltage of the electrochemical device to be used, a current flows through the varistor in an overvoltage state, and the current can be cut off by operating the thermosensitive protection element.

FIG. 2 shows typical voltage-current characteristics of a varistor preferably used in the present invention, and FIG. 3 shows typical voltage-current characteristics of a low-voltage varistor. As is apparent from the figure, when the voltage exceeds a predetermined (varistor) voltage, the current sharply increases. Due to the increased current, heat is generated from the varistor itself, which is transmitted to the heat-sensitive protection element to operate the heat-sensitive protection element.

In the protection element of the present invention, the varistor and the heat-sensitive protection element are thermally connected. Here, being thermally coupled means that the two are close to each other, preferably in contact with each other, so as to have a small heat conduction loss. At this time, the heat transfer loss is desirably 5 ° C. or less, particularly preferably 2 ° C. or less.

Further, in order to reduce the heat transfer loss, both are made of a metal having good thermal conductivity (for example, Cu, Al, Fe,
Ni and their alloys), silicone rubber, silicone grease and the like.

Further, by enclosing both in the same case, good thermal conductivity is obtained and handling is facilitated. As such a case, a resin package, a ceramic package, a metal can, or the like usually used for an electronic device may be used.

The protection element of the present invention is preferably connected and arranged such that the varistor VZ and the electrochemical device E are connected in parallel by an equivalent circuit as shown in FIG. By parallel connection with the electrochemical device in this way, even if the thermosensitive protection element, for example, the thermal fuse does not operate, the varistor is broken down due to the temperature rise, resulting in a short circuit state, and the inside of the electrochemical device is The voltage can be rapidly reduced to prevent an abnormal state such as explosion or ignition.

The heat-sensitive protective element that can be used in the present invention is not particularly limited as long as it can detect a high temperature state and can maintain an electrical cutoff and a high impedance state. PTC thermistors can be mentioned.

PTC stands for Positive Tmperature Coeffc
This is an element whose resistance increases with increasing temperature. Normally, at a certain temperature, the resistance value rises sharply, and the rate of change in resistance is three digits or more, and for some materials, six digits or more. Also, the thermal fuse blows when it exceeds a certain temperature,
It cuts off the current and stops the current.

The heat-sensitive protection element detects abnormal heat generation,
As long as the current can be cut off or limited, other than the above can be used. The operating temperature of the heat-sensitive protective element is preferably 70 to 110 ° C, particularly preferably 80 to 110 ° C.
It is about 95 ° C.

The varistor used in the present invention is preferably a laminated chip varistor. By using a multilayer chip varistor, the mounting volume can be reduced, the device can be made smaller, and thermal coupling becomes easier,
Thermal response is also improved.

The varistor layer constituting the multilayer chip varistor contains, for example, ZnO which is a semiconductor as a main component. Further, in addition to the main component zinc oxide, cobalt oxide (Co
O), praseodymium oxide (Pr ₆ O ₁₁ ), calcium carbonate (CaCO ₃ ), silicon oxide (SiO ₂ ) and the like may be contained in a total of 5% by mass or less. More specifically, based on 98.17% by mass of zinc oxide (ZnO) as a main component,
1.2 mass% of cobalt oxide (CoO), 0.5 mass% of praseodymium oxide (Pr ₆ O ₁₁ ), calcium carbonate (C
aCO ₃ ) 0.1% by mass, silicon oxide (SiO ₂ ) 0.
Those having a concentration of 03% by mass or the like are known. In addition,
Bismuth oxide (Bi ₂ O ₃ ), manganese oxide (Mn)
O), boron oxide (B ₂ O ₃ ), alumina (Al ₂ O ₃ )
Etc. may be mixed.

Silver is used as an electrode of the laminated varistor. However, when this silver external electrode is soldered when chip components are soldered, nickel plating or the like is applied on the silver external electrode. May be applied. Further, tin or tin-lead may be further plated on nickel plating or the like to improve solderability.

The size of the multilayer chip varistor is, for example, about 1.0 to 5.0 mm in length, 0.2 to 2.0 mm in width, and 0.2 to 1.5 mm in height.

The size of the protection element of the present invention depends on the type of the heat-sensitive protection element and the varistor to be used, but is preferably 1.0 to 5.0 mm in length, 0.1 to 2.0 mm in width, and 0.1 to 2.0 mm in width. It is about 0.1 to 10 mm.

The protection element of the present invention is compact and does not require an element or a circuit for driving and controlling the protection element. Therefore, the configuration of the electrochemical device and the circuit associated therewith is simplified, the effective volume is increased, and the volume energy density can be improved.

In consideration of thermal conductivity, this protective element is preferably fixed to an outer bag via a thermal conductive paste and a thermal conductive sheet. As the fixing means, various fixing means such as an adhesive, a tape, a screw, and a pressure bonding by an outer case can be used, but a heat conductive adhesive is preferable. It is preferable that the material for bonding the protective element does not weaken the adhesive strength between -40 ° C and 160 ° C. Specifically, a heat conductive epoxy adhesive or the like can be used.

In attaching a protective element to the surface of an outer bag of an electrochemical device, increasing the maximum thickness of the electrochemical device including the protective element has been required in recent years in electronic equipment such as portable equipment in which the electrochemical device is used. However, it is not preferable in view of the trend toward smaller and thinner devices. Therefore, it is preferable to attach the battery to a place thinner than the maximum thickness of the battery.

Further, the surface temperature of the electrochemical device is not always uniform. The temperature is low in a part where heat is easily radiated and a part with low heat conduction. Therefore, depending on the attaching position, it may operate only at a temperature lower than the temperature of other parts. As a result, the timing of controlling charging is delayed, and it may not be possible to prevent gas generation or ignition.

The electrochemical device used in the present invention comprises:
For example, as shown in FIG. 4, the package includes an outer bag 2, an electrochemical element 3 sealed in the outer bag 2, and a protection element 5 for protecting the electrochemical element 3. And the outer bag 2
The protection element 5 may be arranged at a position where the electrochemical element 3 is not substantially sealed.

It is also preferable that the internal electrode of the electrochemical device, a tab for taking out the internal electrode, or a position where the external electrode is disposed.

As described above, by disposing the protection element at a position where the electrochemical element 3 is not substantially sealed,
The protection element can be mounted without increasing the maximum thickness of the electrochemical device.

That is, as shown in FIG. 4, for example, the electrochemical device 1 includes an electrochemical element 3 sealed in an outer bag 2 and an internal electrode of the electrochemical element 3 or an internal electrode connected thereto. And an external electrode 6 connected to the internal electrode or the extraction tab 4 and led out of the outer bag 2. For this reason, in the region where the electrochemical element 3 is not substantially sealed in the outer bag 2 as shown in the illustrated example, a thin portion in which only the internal electrode or the takeout tab 4 or only the external electrode 6 is sealed. have. Therefore, if the protection element 5 is arranged in this thin portion, an extra space can be effectively used, and the maximum thickness of the electrochemical element 3 itself does not need to be increased.

As shown in FIG. 4, the protection element 5
It is preferable that the internal electrode, a tab for taking out the internal electrode, or a position where the external electrode is disposed. That is, for example, in the case of a lithium secondary battery or the like, the electrochemical device 1 includes a positive electrode (internal electrode), an electrolyte,
It has a structure in which an electrochemical element in which a negative electrode (internal electrode) is laminated is sealed in an outer bag 2. At this time, the external electrode (outgoing terminal) 3 of the electrochemical element is housed in a state of protruding outside, and the opened end face of the outer package 2 is sealed by heat fusion with the external electrode 3 interposed therebetween to form a seal portion. It is configured. Therefore, the internal electrode, the tab for taking out the internal electrode, or the external electrode is made of a metal having relatively excellent thermal conductivity, and the internal heat is easily transmitted. For this reason, by arranging the protection element on the exterior body at the position where these metals are sealed, the operation sensitivity of the protection element is improved.
In other words, the protection element can be operated at a temperature closer to the internal temperature.

Here, the arrangement of the internal electrode, the tab for taking out the internal electrode, or the position where the external electrode is provided means that, in FIG. Means that the projected surface of the protective element overlaps with the projected surface of the protective element from above the paper surface, preferably 50% or more, more preferably 70% or more, particularly 80% or more of the projected surface of the protective element.

The electrochemical element has a structure in which positive and negative electrodes composed of, for example, a metal foil such as an aluminum foil or a copper foil are alternately laminated with a solid polymer electrolyte. External electrodes (lead-out terminals) are connected to the positive and negative electrodes, respectively. The external electrode 3 is made of a metal foil such as aluminum, copper, nickel, and stainless steel. External electrode 3
Has a seal portion in a region covered with the adhesive 7.

The outer bag 2 is made of, for example, polypropylene as a heat-adhesive resin layer on both sides of a metal layer such as aluminum.
It is composed of a laminated film in which a polyolefin resin layer such as polyethylene or a heat-resistant polyester resin layer is laminated. The outer bag 2 is formed in a bag shape with one side opened by previously bonding two laminated films to each other by thermally bonding the thermo-adhesive resin layers on the end surfaces of the three sides to each other. . Alternatively, a single laminated film may be folded back and the both end faces may be thermally bonded to form a seal portion to form a bag.

In order to secure insulation between the metal foil forming the laminate film and the lead-out terminals, the heat-resinable resin layer / polyester resin layer / metal foil / polyester was used as the laminate film forming the outer package. It is preferable to use a laminate film having a laminated structure of resin layers. By using such a laminated film, the high melting point polyester resin layer remains without melting at the time of thermal bonding, so that a separation distance between the lead terminal and the metal foil of the outer package can be ensured, and insulation can be ensured. . Therefore, the thickness of the polyester resin layer of the laminate film is preferably about 5 to 100 μm.

The electrochemical device in the present invention is not limited to a battery such as a lithium secondary battery, and a capacitor having a similar structure can be used.

The electrochemical device according to the present invention can be used as a lithium secondary battery or an electric double layer capacitor as described below.

<Lithium Secondary Battery> Although the structure of the lithium secondary battery is not particularly limited, it is generally composed of a positive electrode, a negative electrode, and a solid polymer electrolyte, and is applied to a stacked battery, a square battery, and the like.

The electrode to be combined with the polymer solid electrolyte may be appropriately selected from those known as electrodes for a lithium secondary battery, and is preferably used as an electrode active material and a gel electrolyte. Is used.

For the negative electrode, a negative electrode active material such as a carbon material, lithium metal, lithium alloy or oxide material is used. For the positive electrode, an oxide or carbon material capable of intercalating / deintercalating lithium ions is used. It is preferable to use such a positive electrode active material as described above. By using such an electrode, a lithium secondary battery having excellent characteristics can be obtained.

The carbon material used as the electrode active material may be appropriately selected from, for example, mesocarbon microbeads (MCMB), natural or artificial graphite, resin fired carbon material, carbon black, carbon fiber and the like. These are used as powders. Above all, graphite is preferred, and its average particle size is preferably 1 to 30 μm, particularly preferably 5 to 25 μm. If the average particle size is too small, the charge / discharge cycle life tends to be short and the variation in capacity (individual difference) tends to be large. If the average particle size is too large, the dispersion of the capacity becomes extremely large, and the average capacity becomes small. It is considered that the capacity variation occurs when the average particle size is large because the contact between the graphite and the current collector and the contact between the graphites vary.

When lithium ions are intercalated on day
Intercalatable oxides include lithium
Complex oxides are preferred, for example, LiCoO_Two, LiM
n_TwoO _Four, LiNiO_Two, LiV_TwoO_FourAnd the like.
The average particle size of these oxide powders is about 1 to 40 μm.
It is preferred that

A conductive assistant is added to the electrode as necessary. Preferred examples of the conductive auxiliary agent include metals such as graphite, carbon black, carbon fiber, nickel, aluminum, copper, and silver. Particularly, graphite and carbon black are preferable.

The electrode composition of the positive electrode is as follows: active material: conductive auxiliary agent: gel electrolyte = 30 to 90: 3 to 10: 1 in weight ratio.
The range of 0 to 70 is preferable. In the negative electrode, active material: conductive auxiliary agent: gel electrolyte = 30 to 90: 0 to 10: 1 by weight ratio.
A range from 0 to 70 is preferred. The gel electrolyte is not particularly limited, and a commonly used gel electrolyte may be used. Also,
An electrode containing no gel electrolyte is also preferably used. In this case, a fluororesin, a fluororubber, or the like can be used as the binder, and the amount of the binder is about 3 to 30% by mass.

In the production of the electrode, first, an active material and, if necessary, a conductive auxiliary are dispersed in a gel electrolyte solution or a binder solution to prepare a coating solution.

Then, this electrode coating solution is applied to a current collector. The means for applying is not particularly limited, and may be determined as appropriate according to the material and shape of the current collector. Generally, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method, and the like are used.
Thereafter, if necessary, a rolling treatment is performed by a flat plate press, a calender roll, or the like.

The current collector may be appropriately selected from ordinary current collectors according to the shape of the device used by the battery and the method of arranging the current collector in the case. Generally, aluminum or the like is used for the positive electrode, and copper, nickel, or the like is used for the negative electrode.
Note that a metal foil, a metal mesh, or the like is generally used as the current collector. Although the metal mesh has lower contact resistance with the electrode than the metal foil, a sufficiently low contact resistance can be obtained even with the metal foil.

Then, the solvent is evaporated to produce an electrode. The coating thickness is preferably about 50 to 400 μm.

The polymer film is made of, for example, PEO (polyethylene oxide), PAN (polyacrylonitrile)
And a polymer microporous membrane such as PVDF (polyvinylidene fluoride).

Such a positive electrode, a polymer film, and a negative electrode are laminated in this order and pressed to form a battery body.

The electrolyte for impregnating the polymer membrane generally comprises an electrolyte salt and a solvent. As the electrolyte salt, for example, Li
BF ₄ , LiPF ₆ , LiAsF ₆ , LiSO ₃ C
Lithium salts such as F ₃ , LiClO ₄ , and LiN (SO ₂ CF ₃ ) ₂ can be used.

The solvent of the electrolytic solution is not particularly limited as long as it has good compatibility with the above-mentioned solid polymer electrolyte and electrolyte salt, but in a lithium battery or the like, a polar organic solvent which does not decompose even at a high operating voltage. Solvents, for example, carbonates such as ethylene carbonate (abbreviation EC), propylene carbonate (abbreviation PC), butylene carbonate, dimethyl carbonate (abbreviation DMC), diethyl carbonate, ethyl methyl carbonate, etc., tetrahydrofuran (THF), 2-methyltetrahydrofuran and the like A cyclic ether, a cyclic ether such as 1,3-dioxolan, 4-methyldioxolan, a lactone such as γ-butyrolactone, a sulfolane, and the like are preferably used. 3-Methylsulfolane, dimethoxyethane, diethoxyethane, ethoxymethoxyethane, ethyldiglyme and the like may be used.

When it is considered that the electrolyte is composed of the solvent and the electrolyte salt, the concentration of the electrolyte salt is preferably 0.3 to 5 mol.
l / l. Usually, it exhibits the highest ionic conductivity at around 1 mol / l.

When a microporous polymer film is immersed in such an electrolytic solution, the polymer film absorbs the electrolytic solution and gels to form a solid polymer electrolyte.

When the composition of the solid polymer electrolyte is represented by copolymer / electrolyte, the ratio of the electrolyte is preferably 40 to 90% by mass in view of the strength of the membrane and the ionic conductivity.

<Electric Double Layer Capacitor> Although the structure of the electric double layer capacitor of the present invention is not particularly limited, usually, a pair of polarizable electrodes are arranged via a polymer solid electrolyte, and the polarizable electrode and the polymer An insulating gasket is arranged around the solid electrolyte. Such an electric double layer capacitor may be any type called a paper type, a laminated type, or the like.

As the polarizable electrode, activated carbon, activated carbon fiber, or the like is used as a conductive active material, and a fluororesin, fluororubber, or the like is added as a binder. Then, it is preferable to use the mixture formed on a sheet-like electrode. The amount of the binder is about 5 to 15% by mass. Further, a gel electrolyte may be used as the binder.

The current collector used for the polarizable electrode is platinum,
It may be a conductive rubber such as a conductive butyl rubber or the like, may be formed by spraying a metal such as aluminum or nickel, or may be provided with a metal mesh on one surface of the electrode layer.

The electric double layer capacitor is formed by combining the above-mentioned polarizable electrode and a solid polymer electrolyte.

The polymer film is made of, for example, PEO (polyethylene oxide), PAN (polyacrylonitrile)
And a polymer microporous membrane such as PVDF (polyvinylidene fluoride).

As the electrolyte salt, (C ₂ H ₅ ) ₄ NB
F ₄ , (C ₂ H ₅ ) ₃ CH ₃ NBF ₄ , (C ₂ H ₅ ) ₄ PB
F _4, and the like.

The non-aqueous solvent used for the electrolytic solution may be various known ones, and propylene carbonate, ethylene carbonate, γ-
Butyrolactone, acetonitrile, dimethylformamide, 1,2-dimethoxyethane, sulfolane alone or a mixed solvent is preferred.

The concentration of the electrolyte in such a non-aqueous solvent-based electrolyte solution may be 0.1 to 3 mol / l.

When a microporous polymer film is immersed in such an electrolytic solution, the polymer film absorbs the electrolytic solution and gels to form a polymer solid electrolyte.

When the composition of the solid polymer electrolyte is represented by copolymer / electrolyte, the ratio of the electrolyte is preferably 40 to 90% by mass from the viewpoint of the strength of the membrane and the ionic conductivity.

As the insulating gasket, an insulator such as polypropylene or butyl rubber may be used.

[0075]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. <Example> As a fuse used in this example, DC24V 5
Those with A or more were used. The chip-type varistor is obtained by adding various oxides and the like as additives with oxidized oxide as a main component, followed by firing. As the varistor voltage,
A voltage of 4 to 6 V was used. The arrangement of the protection element composed of the varistor and the fuse was as shown in FIGS. The size of this protection element was 5 mm in length, 12 mm in width, and 2 mm in height.

Comparative Example As a comparative example, a fuse in which a varistor was not thermally coupled was used. In this case, in order for the fuse to function, the object needs to generate heat.

The characteristics of the lithium ion secondary battery at the time of overcharging were evaluated using the protection elements of the above Examples and Comparative Examples. Table 1 shows the results.

[0078]

[Table 1]

As can be seen from this table, the protection device according to the embodiment of the present invention can be used regardless of the thermal state of the object.
When the overcharge voltage of the battery reaches 4.5 V or more, the varistor functions, the fuse operates, and the current is cut off. On the other hand, in the case of only the fuse, the protection may be performed depending on the time of the current cutoff, or the ignition may occur, and the protection function is not reliable.

Although the present invention has been described using a lithium ion secondary battery, the present invention can be applied to any lithium secondary battery using lithium ion conductivity. Also, the present invention can be applied to other secondary batteries and electronic devices for the purpose of protecting a voltage from overcurrent.

[0081]

As described above, according to the present invention, protection for an electrochemical device which can be operated reliably even in an overvoltage state with a simple structure, a small load on a circuit, no restriction on a mounting place, and the like. An element can be provided.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram of the electrochemical device of the present invention.

FIG. 2 is a graph showing voltage-current characteristics of a varistor.

FIG. 3 is a graph showing voltage-current characteristics of a varistor.

FIG. 4 is a schematic side view showing the structure of an electrochemical device.

FIG. 5 is a plan view of FIG. 4;

FIG. 6 is a block diagram showing a conventional protection circuit for a secondary battery.

FIG. 7 is a block diagram showing a conventional protection circuit for a secondary battery using a built-in resistor type thermal fuse.

[Explanation of symbols]

 2 outer bag 3 electrochemical element 4 tab 5 protective element 6 external electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5E034 CA04 CA07 CA09 DD03 EA08 EC03 5H022 AA09 CC16 KK01 5H029 AJ12 AJ14 AK03 AL06 AL07 AM02 AM03 AM04 AM07 AM16 DJ05

Claims (5)

[Claims] 1. A protection element for an electrochemical device as a protection element for protecting an electrochemical device, wherein a varistor and a heat-sensitive protection element are thermally coupled, and a temperature rise of the varistor causes the heat-sensitive protection element. A protective element for electrochemical devices that operates. 2. The protection device for an electrochemical device according to claim 1, wherein said varistor is a multilayer chip varistor. 3. The protection device for an electrochemical device according to claim 1, wherein the varistor and the heat-sensitive protection device are enclosed in the same case. 4. The varistor and the electrochemical device are connected such that an equivalent circuit is connected in parallel.
Any of the electrochemical devices. 5. The protection device for an electrochemical device according to claim 1, wherein the electrochemical device is a lithium secondary battery.