JP2002358947A - Electrochemical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical device that can be improved in safety by operating a small size protection element rapidly in an electrochemical device having a protection element. SOLUTION: This is an electrochemical device in which a thermosensible protection element 4 that is operated by temperature is fitted to an electrochemical element 2 and sealed by an outer case 3. When the heat resistance between the thermosensible protection element 4 and the outer case 3 is R1, and the heat resistance between the thermosensible element 4 and the electrochemical element 2 is R2, and constant is A, the electrochemical device satisfies; R1=A×R2, 1<A<=100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrochemical device for storing electricity such as a lithium ion battery, a polymer lithium secondary battery, and an electric double layer capacitor, and more particularly, to an electrochemical device having a safety mechanism against heat generation. The present invention relates to a device manufacturing method.

[0002]

2. Description of the Related Art With the spread of portable electronic devices, there is a demand for electrochemical devices such as secondary batteries which are lightweight, compact and can be used continuously for a long time. Conventional secondary batteries use metal outer cans, but as represented by lithium polymer batteries, use thin and light films for outer bags to reduce battery weight and increase design flexibility. It became possible.

[0003] The film used for the outer bag is an aluminum laminated film in which an aluminum foil is mainly coated with several kinds of resins. This aluminum laminated film is light in weight, and can be made thinner and lighter than a battery using a conventional metal outer can.

Conventionally, when any abnormality occurs in a battery using such a film as an outer bag, depending on the type of electrolyte used, gas may be generated or, in the worst case, ignition may occur. For example, the charger is set to stop charging when a predetermined time or voltage is reached, but if charging is not stopped for any reason, the battery exceeds the capacity of the battery and is overcharged. When the overcharge state further progresses, the electrolyte is decomposed, gas is generated, and the outer bag expands, and then the bag bursts or ignites.

[0005] In order to avoid such a situation, the battery is usually provided with some kind of protection circuit. Usually, this protection circuit often has a function of preventing a current from flowing when a predetermined voltage is reached.

[0006] In consideration of the case where the protection circuit does not function for some reason, various studies have been made to provide other protection means. One of the protection methods is a PTC element or a heat-sensitive protection element such as a thermal fuse.

[0007] PTC stands for Positive Tmperature Coefic.
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.

Generally, a charger supplies a constant current up to a predetermined voltage, and then controls the current at the predetermined voltage. When the battery generates heat due to some abnormality during charging, the PTC element is heated and the resistance increases. Thereby, the charging current is suppressed, and further charging is suppressed. When the temperature fuse exceeds a certain temperature, the charging current is cut off and charging is stopped. It is widely known that a secondary battery using lithium ion causes thermal runaway when a certain temperature is exceeded. Heat runaway
Generates gas and additional heat, causing battery explosion and fire. Therefore, it is necessary to reduce or cut off the current before the temperature of the battery enters a dangerous area.

In order to reduce the size of the device, it is necessary to reduce the size of the battery pack itself. When a protection circuit is not provided, it is necessary to reduce or cut off the current at an early stage in the event of an abnormality in order to ensure protection, and the installation of a protection element is effective.

[0010] Regarding the effectiveness of the protection element, see Japanese Patent No. 303
No. 5677. The installation of the protection element inside the exterior material is described in Japanese Patent Application Laid-Open No. 1-67188. However, the only protection element studied in this document is a thermal fuse, which is directly connected to a lead terminal extraction portion. Further, the battery of this document is a wound type battery, and it is difficult to apply this structure to a stacked type as it is. Furthermore, since the protection element is arranged in the thickness direction of the battery element, the thickness of the battery increases accordingly, and the volume energy density decreases.

On the other hand, installing the protection element outside the battery hinders the miniaturization of the battery pack, and the amount of heat transmitted to the element is reduced outside due to the thermal resistance of the exterior material and the heat radiation from the entire battery. Early operation is difficult. In addition, it is not preferable to attach the protection element in the thickness direction of the electrochemical device because the volume energy density is reduced.

Therefore, it is desirable to install the protection element inside the exterior material having good heat conductivity without changing the battery size.
At this time, the protection element is desired to have a size that does not change the size of the battery, including the exterior material, and that the function of the element does not change even when touched with the electrolyte, and that the characteristics of the battery are adversely affected. Is not affected.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrochemical device using a protective element, which is small in size and capable of improving safety more than operating the protective element quickly. It is to provide.

[0014]

That is, the above object can be attained by the following constitution of the present invention. (1) An electrochemical device in which a thermosensitive protection element that operates according to temperature is attached to an electrochemical element and sealed with an exterior material, wherein the thermal resistance between the thermosensitive protection element and the exterior material is R1, When the thermal resistance between the element and the element is R2 and the constant is A, R1 = A × R2, and 1 <A ≦ 10
An electrochemical device that is zero. (2) By providing a space between the heat-sensitive protection element and the exterior material, or by arranging a material having a high thermal resistance, the thermal resistance R1 between the protection element and the exterior material is adjusted to be large. The electrochemical device according to (1) above. (3) Part or all of the heat-sensitive protective element is made of polypropylene, polyethylene, acid-modified polypropylene,
The electrochemical device according to (1) or (2), wherein one or more resins selected from acid-modified polyethylene, epoxy resin, and modified isocyanate are used, and the resin is sealed. (4) The electrochemical device according to any one of (1) to (3), wherein the heat-sensitive protective element is disposed between the positive and negative electrode lead-out terminals of an electrochemical element. (5) The electrochemical device according to any one of (1) to (4), wherein the thermosensitive protection element has a size not exceeding a thickness of the electrochemical element body.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An electrochemical device according to the present invention is an electrochemical device in which a thermosensitive protection element that operates according to temperature is attached to an electrochemical element and sealed with an exterior material.
When the thermal resistance between the thermosensitive protection element and the exterior material is R1, the thermal resistance between the electrochemical element and R2 is a constant, and A is a constant, R1 = A × R2, and 1 <A ≦ 100.

As described above, the thermal resistance R1 between the heat-sensitive protective element and the exterior material is made larger than the thermal resistance R2 between the heat-sensitive protective element and the electrochemical element, so that heat is radiated from the protective element to the outside. Reduces the sensitivity of the thermosensitive protection element,
The response speed is improved, and the heat-sensitive protection element can be quickly and reliably operated.

As shown in FIGS. 1 and 2, for example, the electrochemical device of the present invention comprises an exterior material 3, an electrochemical element 2 housed in the exterior material 3, and a heat-sensitive protection element 4 for protecting the same. It has. Further, the electrochemical element 2
The heat-sensitive protection element 4 is connected and arranged between the current collector tabs 5a and 6a and the leads 5b and 6b for leading a current out of the exterior material 3. Here, FIG. 1 is an external perspective view showing a configuration example of an electrochemical device, and FIG. 2 is a plan view. In the drawings, the exterior body is indicated by a broken line.

Here, the thermal resistance between the heat-sensitive protective element 4 and the exterior material 3 is R1 [° C./W], and the thermal resistance between the heat-sensitive protective element 4 and the electrochemical element 2 is R2 [° C.]. / W], R1 = A × R2. Here, A is a constant, and 1 <A ≦ 100, preferably 2 ≦ A ≦ 50, and more preferably 5 ≦ A ≦ 30.

The above condition can be satisfied by arranging a material having high thermal resistance between the heat-sensitive protective element 4 and the exterior material 3 or providing a gap (space) between the heat-sensitive protection element 4 and the exterior material. . With such a structure, heat radiation from the protection element can be reduced, and the protection element can be activated at an early stage.

Examples of the material having high thermal resistance include resin materials such as polypropylene, polyethylene, epoxy and polyester, and ceramics. There is no.

Further, instead of inserting a material having a large thermal resistance between the exterior material and the protective element, a material having a large thermal resistance satisfying the above conditions is placed on the surface of the heat-sensitive protective element facing the exterior material. They may be arranged in advance.

The heat-sensitive protective element used in the present invention is not particularly limited as long as it detects the heat generated by the current itself or the heat generated by the electrochemical element and cuts off or restricts the current at a predetermined temperature. It suffices if the condition of the predetermined size is satisfied.

Specifically, a thermal fuse, a PTC element, and the like can be given, and these must operate without deteriorating the characteristics even when they come in contact with the electrolytic solution. In order to protect the thermosensitive protection element from the electrolytic solution, it is preferable to cover with a resin. However, the resin material is not particularly limited as long as it is not affected by the electrolytic solution. However, considering the adhesiveness of the protective element to the terminal, acid-modified polypropylene, acid-modified polyethylene, epoxy resin, modified isocyanate is preferable,
Particularly, acid-modified polypropylene is preferable. It is desirable to cover and seal the entire protection element with such a resin, but it is also possible to cover the protection element with a resin such as polyethylene and use only a bonding portion between the lead and the polyethylene as a sealing material to seal.

The thickness of the resin film such as acid-modified polypropylene is 10 μm to 300 μm, preferably 30 μm to 2 μm.
00 μm, more preferably 50 μm to 100 μm.

The heat-sensitive protective element is connected between the lead of the electrochemical element and the current collecting tab so that a current flows through the heat-sensitive protective element. That is, one of the lead terminals of the thermosensitive protection element is connected to the lead terminal of the electrochemical device, and the other lead terminal is connected to the current collecting tab of the device. The connection method includes ultrasonic welding, electric spot welding, and the like, but is not particularly limited.

Preferably, the heat-sensitive protective element is disposed on the side of the electrochemical element body where the current collecting tab is located. At this time, it is preferable to arrange the heat-sensitive protection element so that the plane portion (the surface having the maximum area) is parallel to the thickness direction of the electrochemical element. Thus, the protection element can be built in without changing the dimensions of the device.

Here, the thickness Dp of the heat-sensitive protective element 4 shown in FIG. 3 is shorter than the length Ll of the current lead-out lead inside the current collector tab or the exterior material, and the width Wp is the thickness of the electrochemical element. It is thinner than Dc and the length Lp is the distance L between the current lead-outs.
It may be shorter than s. By setting the heat-sensitive protective element to such a size, the heat-sensitive protective element can be accommodated without changing the size of the battery itself.

The electrochemical device thus produced is sealed with an exterior material.

The electrochemical element has a structure in which positive and negative electrodes composed of a metal foil such as an aluminum foil or a copper foil and a solid polymer electrolyte or a separator are alternately laminated or wound. 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. The external electrode 3 has a seal portion in a region covered with the adhesive 7.

The exterior material is made of, for example, a metal can made of aluminum or the like, a metal laminated film, or the like. Examples of the metal laminate film include a laminate film in which a polyolefin resin layer such as polypropylene or polyethylene as a heat-adhesive resin layer or a heat-resistant polyester resin layer is laminated on both surfaces of a metal layer such as aluminum. The metal laminated film is formed in a bag shape with one side opened by forming two first laminated films by heat bonding the thermo-adhesive resin layers on the end faces 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.

The current lead-out terminal is sandwiched by a laminate film constituting an outer package, and a metal layer directly laminated on the external electrode 3 is provided between the lead terminal and the heat-adhesive resin layer of the laminate film. An adhesive between resins may be provided.

Examples of the metal-resin adhesive include acid-modified polyethylene such as carboxylic acid, acid-modified polypropylene, epoxy resin, and modified isocyanate. Since the metal-resin adhesive is provided between the metal and the polyolefin resin to improve the adhesion between them, it is sufficient that the adhesive covers the sealing portion of the lead-out terminal 3. .

In order to secure insulation between the metal foil forming the laminate film and the lead-out terminal, a heat-adhesive resin layer / polyester resin layer / metal foil / polyester is 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 element used in the electrochemical device of 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 of 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 of the present invention is not particularly limited, it is usually composed of a separator such as a positive electrode, a negative electrode and a polymer film or a solid electrolyte, and is a laminated battery or a square battery. And so on.

The electrode combined with the separator and the solid polymer electrolyte may be appropriately selected from those known as electrodes of a lithium secondary battery, and is preferably used as an electrode active material and a gel electrolyte. A composition with the agent 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.

Lithium ion is intercalated 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

If necessary, a conductive additive is added to the electrode. 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 by weight.
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 an 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, the method of disposing the current collector in the case, and the like. 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).

The positive electrode, the polymer film, and the 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 such as ethylene carbonate (EC), propylene carbonate (P
C), butylene carbonate, dimethyl carbonate (DMC), carbonates such as diethyl carbonate and ethyl methyl carbonate, tetrahydrofuran (T
HF), cyclic ethers such as 2-methyltetrahydrofuran, cyclic ethers such as 1,3-dioxolane and 4-methyldioxolane, lactones such as γ-butyrolactone, 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 is 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, a 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 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.

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

[0065]

The present invention will be further described below with reference to examples.

<Example 1> Melting temperature (operating temperature) 95 ° C
Was processed into a diameter of 0.3 mm and a length of 3 mm to prepare a thermal fuse element. Both ends were welded to a nickel foil, a flux was applied around the element, and then sealed with an acid-modified polypropylene having a thickness of 0.1 mm to form a thermal fuse.

Here, a thickness of 0.5 mm was applied to one side of the thermal fuse.
mm polypropylene film was adhered to increase the thermal resistance on one side.

The thermal fuse thus produced was connected to an electrochemical element as shown in FIG. At this time, the connection was performed such that the surface having a low thermal resistance was opposed to the battery body. The battery element with the protection element was put in an outer bag made of a laminate film, injected with an electrolytic solution, and sealed to prepare a battery.
The sealing was performed by heat sealing the laminated film. At this time, R1 = 20 ° C./W, R2 = 120 ° C./W
And A = 6.

<Comparative Example 1> A battery was prepared in the same manner as in Example 1, except that a polypropylene film having a thickness of 0.5 mm was not provided on one side of the thermal fuse. At this time, R1 = 20 ° C./W, R2 = 20 ° C./W, and A =
It was one.

<Comparative Example 2> A battery was prepared by attaching a thermal fuse prepared in the same manner as in Example 1 to the outside of the outer package.

<Comparative Example 3> A battery was prepared in the same manner as in Comparative Example 1, except that no thermal fuse was provided.

Each of the five batteries prepared as described above, 6 V
After reaching a constant current of 1 A and 6 V, an abnormal charging test was performed by controlling the current so as to become a constant voltage. Table 1 shows the results.

[0073]

[Table 1]

As is clear from Table 1, it is clear that the fuse is activated early by installing the thermal fuse inside the battery. Further, by suppressing the heat radiation of the thermal fuse, the thermal fuse can be operated more quickly.

As is clear from the above description, the safety at the time of heat generation is improved by installing the thermal fuse inside the exterior body and suppressing heat radiation on the surface facing the exterior material.

[0076]

As described above, according to the present invention, in an electrochemical device using a protective element, an electrochemical device that is small in size and capable of quickly operating the protective element to improve safety is provided. Can be provided.

[Brief description of the drawings]

FIG. 1 is an external perspective view showing a basic configuration of an electrochemical device.

FIG. 2 is a plan view showing a basic configuration of an electrochemical device.

FIG. 3 is an external perspective view of a heat-sensitive protection element.

[Explanation of symbols]

 2 electrochemical element 3 exterior material 4 heat-sensitive protective element

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H022 AA09 CC12 EE01 EE06 EE10 KK01 5H029 AJ12 AK03 AL06 AL07 AL08 AL12 AM02 AM03 AM04 AM05 AM07 AM16 BJ02 BJ06 EJ12 HJ20

Claims (5)

[Claims] 1. An electrochemical device comprising a thermosensitive protection element, which operates according to temperature, attached to an electrochemical element and sealed with an exterior material, wherein the thermal resistance between the thermosensitive protection element and the exterior material is R1, An electrochemical device wherein R1 = A × R2, where 1 <A ≦ 100, where R2 is a thermal resistance between the electrochemical element and a constant is A. 2. An adjustment is made such that a space is provided between the heat-sensitive protection element and the exterior material, or a material having a large thermal resistance is disposed to increase the thermal resistance R1 between the protection element and the exterior material. The electrochemical device of claim 1, wherein 3. One or more resins selected from the group consisting of polypropylene, polyethylene, acid-modified polypropylene, acid-modified polyethylene, epoxy resin, and modified isocyanate are used for part or all of the heat-sensitive protective element. 3. The electrochemical device according to claim 1, wherein the device is closed and sealed. 4. The electrochemical device according to claim 1, wherein said heat-sensitive protective element is disposed between the positive and negative electrode lead-out terminals of an electrochemical element. 5. The electrochemical device according to claim 1, wherein the heat-sensitive protective element has a size not exceeding a thickness of the electrochemical element.